Name: metal-free synthesis of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts
Uploaded: 2015-02-24T14:00:00.000+00:00
Duration: 9 min 58 s
Description: Watch this Scientific Journal Video about Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts at JoVE.com

This work was supported by the UOIT start-up fund. We thank Mr. Matthew Baxter (UOIT) for his assistance in the laboratory.

1. Síntesis de Ynone <ol><li> Utilizando una balanza analítica, pesar 0,15 mmol de la sal de potasio alkynyltrifluoroborate deseado (1,5 equivalentes) y se añade a un vial limpio equipado con una barra de agitación magnética. </li><li> El uso de un émbolo de la jeringa de vidrio equipado con una aguja, añadir 0,5 ml de DCM anhidro para el vial para proporcionar una solución de 0,3 M trifluoroborato. NOTA: Como se trata de una nueva metodología, se han realizado las reacciones de prueba de concepto. Con el fin de reducir los residuos que se han realizado en una pequeña escala. La reacción puede hacerse a escala para producir mayores rendimientos según sea necesario. </li><li> Usando una jeringa de vidrio, añadir 0,15 mmol de una solución de tricloruro de boro 1,0 M (1,5 equivalentes, 150 ml) gota a gota al recipiente de reacción a temperatura ambiente (20 ° C) con agitación. Reemplace la tapa. Retener o sujetar el recipiente de reacción tapado de tal manera que la solución de reacción está por debajo de la línea de agua en el baño de ultrasonidos. Sonicar la solución durante 30 segundos a 20 ° C y una o frecuenciaf 40 kHz. </li><li> Se agita la solución de reacción a temperatura ambiente (20 ° C) durante un adicional de 20 min. Dependiendo de la naturaleza del material de partida alkynyltrifluoroborate, observar un cambio de color. Un cambio de color de blanco a marrón claro o marrón oscuro, rojo o púrpura es común. </li><li> Añadir 0,1 mmol del cloruro de acilo deseado (1,0 equivalente) en el vial a temperatura ambiente (20 ° C) con agitación. Alternativamente, transferir el contenido del recipiente de reacción a un matraz cargado con una barra de agitación magnética y 0,1 mmol de cloruro de acilo. Reemplace la tapa. Se agita la solución de reacción a temperatura ambiente (20 ° C) durante 30 min. NOTA: Por lo general, un cambio a un color muy oscuro es una indicación de que la reacción está teniendo lugar. </li><li> Usando una cromatografía en capa fina (TLC) 34 supervisar el progreso de la reacción mediante la comparación con el estándar de cloruro de acilo apropiado. NOTA: En función de la naturaleza de los materiales de partida, la reacción no puede llegar a su finalización. La unamaterial de partida cloruro de cilindros se ha observado como un punto de funcionamiento más alta que el producto final para todos los ynones preparados hasta la fecha usando este método. <ol><li> Preparar el estándar de cloruro de acilo mediante la dilución de aproximadamente 10 mg de cloruro de acilo material de partida con 1 ml de acetato de etilo en un pequeño vial. </li><li> El uso de un observador de tiro TLC, detectar la solución de reacción y la serie en la línea de salida de la placa de TLC. Un co-spot tanto con la solución de reacción y el nivel puede ser útil para determinar si hay material presente en la solución de reacción todavía de partida. </li><li> Determinar una fase móvil TLC adecuado por ensayo y error. Para la preparación de producto 1a, una fase móvil que consiste en 01:30 acetato de etilo: hexanos resultados en los valores de R f de aproximadamente 0,5 y 0,8 para el producto ynone y cloruro de benzoilo material de partida, respectivamente. </li><li> Visualice la placa de TLC desarrollado bajo la luz ultravioleta. Use un lápiz para marcar las manchas visibles. </li></ol></li></ol> 2. acuosa Workup <ol><li> Interrumpir la reacción mediante la adición de 1 ml de agua fría (aproximadamente 5 ° C) al recipiente de reacción. Utilizando una pipeta Pasteur, transferir la solución a un embudo de separación limpia. Además diluir el contenido del embudo de decantación con 10 ml de agua fría y extraer el producto una vez en 15 ml de acetato de etilo. </li><li> Desechar la capa acuosa inferior y se lava la capa orgánica una vez adicional con 10 ml de agua y una vez con 10 ml de salmuera. Recoger la fase orgánica en un matraz Erlenmeyer limpia y seca con sulfato de magnesio. Filtrar la solución en un matraz de fondo redondo limpio usando filtración por gravedad. </li></ol> 3. Purificación de Ynone <ol><li> El uso de cromatografía de capa fina, determinar una fase móvil adecuado para la purificación cromatografía ultrarrápida del producto. Un factor de retención (R f) de aproximadamente 0,5 es generalmente suficiente para separar el producto de cualquier inicio restanteing materiales y productos secundarios. NOTA: En el caso de una mala separación, un sistema disolvente menos polar puede ser utilizado de tal manera que el producto tiene un valor R f inferior. Dependiendo de la polaridad de los materiales de partida, una mezcla de hexanos: acetato de etilo en el intervalo de 30: 1 a 5: 1 es generalmente adecuada. </li><li> Preparar una columna que contiene sílice húmeda con la fase móvil adecuada. Añadir una capa de arena de la parte superior de la columna con el fin de evitar molestar a la sílice después de la adición del producto y eluyente. </li><li> Evaporar la solución estudio diagnóstico usando un evaporador rotatorio con la temperatura del baño a 40 ° C y la rotación ajustado a 120 rpm. Disolver el contenido del matraz en un 2 ml de fase móvil y cargar cuidadosamente la solución de manera uniforme en la columna. Asegúrese de que la sílice está mojado pero la línea de disolvente no excede la altura de la sílice. Permitir algún disolvente para eluir tal que el producto se encuentra en la sílice. Agregue una pequeña cantidad de la fase móvil y repetir. </li><li> Llene el colUMN con la fase móvil determinado en el paso 3.1; en el caso de producto 1a, una 30: 1 mezcla de hexanos: acetato de etilo es apropiado. Reunir las fracciones en tubos de ensayo, usando la cromatografía flash para acelerar el proceso de purificación. Sólo tienes que conectar un adaptador con un tubo a una salida de aire. Ajustar la presión de aire de tal manera que el eluyente fluye a través de la columna a una velocidad adecuada. </li><li> Detectar cada una de las fracciones de la columna en una placa de TLC. Opcionalmente, detectar el estándar de cloruro de acilo como referencia. Desarrollar el TLC utilizando la fase móvil se considere apropiado en el paso 1.8. Marque los puntos visibles bajo luz ultravioleta, y señaló que se espera que el producto tenga un Rf más bajo que el estándar de cloruro de acilo. </li><li> Recoge todas las fracciones que contenían manchas visibles en un gran matraz de fondo redondo. Si más de un punto con un Rf menor que el material de partida está presente, recogerlos en frascos separados. Se evapora el disolvente utilizando un evaporador rotatorio y se seca el material recogido under alto vacío durante dos horas. </li><li> Si es necesario, realizar un lavado de pentano en una pequeña columna con el fin de purificar adicionalmente un producto preparado a partir de un ynone pobre material de partida cloruro de acilo de electrones. A pequeña escala, esto puede llevarse a cabo utilizando una pipeta Pasteur como la columna. <ol><li> Se disuelve el producto en una cantidad mínima de cloroformo, DCM, o éter dietílico y se carga en una columna de sílice húmeda con pentano. Eluir 1-2 longitudes de columna de pentano a través de la columna y recoger en un vaso de precipitados de residuos. </li><li> Eluir la ynone producto puro de la columna de pentano usando éter dietílico o acetato de etilo. Recoger eluyente en un matraz separado, se evapora, y se coloca bajo alto vacío durante un mínimo de dos horas. Obtener aproximadamente 10 mg de producto para la caracterización por espectroscopía de RMN. </li></ol></li></ol> 4. Caracterización de Ynone <ol><li> Caracterizar y evaluar la pureza del producto final usando 1 H y 13 C RMN espectroscopia. 34Típicamente, el desplazamiento químico del carbono del carbonilo aparece cerca de 177 ppm en el espectro de 13 C RMN. Los dos carbonos SP del grupo funcional ynone están representados por picos característicos cerca de 87 y 93 ppm. </li><li> Utilice la espectroscopia infrarroja 34 para identificar el pico carbonilo característica del producto ynone. Electron deslocalización de la triple enlace adyacente por lo general hace que el pico de carbonilo a aparecer entre 1600 y 1650 cm -1, en ​​función de las características electrónicas del compuesto. </li><li> Determinar la masa molecular del producto y validar la identidad mediante espectrometría de masas de alta resolución. 34 </li></ol>

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W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+student's+lab+companion:+laboratory+techniques+for+organic+chemistry:+standard+scale+and+microscale.">The student's lab companion: laboratory techniques for organic chemistry: standard scale and microscale.</a> Pearson College Div. , (2008).</li><li>Molander, G. A., Cavalcanti, L. N., Canturk, B., Pan, P. -. S., Kennedy, L. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Efficient+Hydrolysis+of+Organotrifluoroborates+via+Silica+Gel+and+Water.">Efficient Hydrolysis of Organotrifluoroborates via Silica Gel and Water.</a> 74, 7364-7369 (2009).</li><li>Molander, G. A., Ellis, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Organotrifluoroborates:+protected+boronic+acids+that+expand+the+versatility+of+the+Suzuki+coupling+reaction.">Organotrifluoroborates: protected boronic acids that expand the versatility of the Suzuki coupling reaction.</a> Acc. Chem. Res. 40, 275-286 (2007).</li><li>Calloway, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Friedel-Crafts+Syntheses.">The Friedel-Crafts Syntheses.</a> Chem. Rev. 17, 327-392 (1935).</li><li>Gore, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Friedel-Crafts+acylation+reaction+and+its+application+to+polycyclic+aromatic+hydrocarbons.">The Friedel-Crafts acylation reaction and its application to polycyclic aromatic hydrocarbons.</a> Chem. Rev. 55, 229-281 (1955).</li><li>Groves, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Friedel&#8211;Crafts+acylation+of+alkenes.">The Friedel&#8211;Crafts acylation of alkenes.</a> Chem. Soc. Rev. 1, 73-97 (1972).</li><li>Kim, B. J., Matteson, D. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Conversion+of+alkyltrifluoroborates+into+alkyldichloroboranes+with+tetrachlorosilane+in+coordinating+solvents.">Conversion of alkyltrifluoroborates into alkyldichloroboranes with tetrachlorosilane in coordinating solvents.</a> Angew. Chem. 116, 3118-3120 (2004).</li><li>Thompson, L., Doraiswamy, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sonochemistry:+science+and+engineering.">Sonochemistry: science and engineering.</a> Ind. Eng. Chem. Res. 38, 1215-1249 (1999).</li></ol>

The authors declare that they have no competing financial interests.

La Tabla 1 ilustra las medidas adoptadas para optimizar las condiciones para la reacción de trifluoroborato fenilacetileno con cloruro de benzoilo para formar el producto ynone correspondiente. Inicialmente, los catalizadores conocidos para convertir organotrifluoroborates a organodifluoroboranes se probaron. Desafortunadamente gel de sílice, 35 tetracloruro de silicio, 36 y trifluoruro de boro 31,32 no promovió la formación de la ynone deseada (Tabla 1, entradas 1-3). El uso de catalizadores clorados ácidos de Lewis resultó ser más exitoso. Un bajo rendimiento de la ynone 1a deseado se obtuvo en presencia de un hierro (III) catalizador de cloruro de (Tabla 1, entrada 4). A continuación, cloruro de aluminio (III) se investigó como resultado de su capacidad bien establecida para promover la formación de iones Oxocarbenio en acilaciones de Friedel-Crafts. 37-39 El producto deseado se obtuvo con un rendimiento del 62% cuando un aluminio (III) catalizador de cloruro era empLoyed. La optimización adicional reveló que el aire y la humedad tienen poco efecto sobre el rendimiento de la reacción (Tabla 1, entradas 5-7). Como resultado, las reacciones posteriores se realizaron en material de vidrio no se seca en la presencia de aire. Los intentos para optimizar el disolvente revelaron que diclorometano (DCM) se adapta particularmente bien a la reacción (Tabla 1, entradas 8-12). Las inconsistencias en los resultados de las reacciones catalizadas por cloruro de aluminio (III) impulsaron la exploración de catalizadores alternativos. Comercialmente disponible de aluminio (III) hexahidrato de cloruro era completamente inactivo en las condiciones de reacción (Tabla 1, entrada 13). Este es un buen indicador de que la formación de cloruro de aluminio (III) hidrato inhibe la reacción. Tricloruro de boro se encontró para producir rendimientos similares con mejor consistencia (Tabla 1, entrada 14). Tras la interacción de la alkynyltriflu de potasiooroborate con tricloruro de boro, se forma una especie organodichloroborane más reactivos. 40 Este paso inicial es crítica para la reacción con el cloruro de acilo y la formación de la ynone para proceder. Desde sales organotrifluoroborate no son solubles en DCM, la reacción se lleva a cabo como una mezcla heterogénea. Después de la adición de tricloruro de boro, la solución se sometió a ultrasonidos para facilitar la formación de las especies reactivas dicloroborano mediante el aumento de la superficie de la sal de trifluoroborato disponible para reaccionar. La aplicación de ondas de ultrasonido a la mezcla de reacción provoca efectos mecánicos a través de la generación de burbujas de cavitación. Durante la sonicación, el colapso de las burbujas de cavitación en los resultados de fluidos en zonas localizadas de las altas temperaturas y presiones. 41 Las ondas de choque se producen turbulencias que crean microscópica resulta en un aumento en la energía cinética de las sales de trifluoroborato sólidos. El aumento en la energía del sistema durante promo sonicaciónTES fragmentación de la sal de trifluoroborato resultante aumentó área de superficie disponible para interactuar con tricloruro de boro. La sonicación de la mezcla de reacción antes de la adición del material de partida cloruro de acilo asegura la formación eficiente de las especies reactivas alkynyldichloroborane sin la necesidad de condiciones forzando más o tiempos de reacción más largos. La Figura 2 ilustra los resultados obtenidos cuando trifluoroborato fenilacetileno se hizo reaccionar con una variedad de cloruros de acilo bajo las condiciones de reacción optimizadas. Neutral aromático (1b, 1c) y alifáticos (1j-l) cloruros de acilo amueblar las ynones correspondientes en los rendimientos sintéticamente útiles. Estos cloruros de acilo que llevan grupos donadores de electrones (1d-g) proporcionan excelentes rendimientos mientras que los grupos aceptores de electrones resultan en rendimientos comparativamente modestos (1h, 1i, 1m). Interestingly, cuando el grupo aceptor de electrones se encuentra en la posición orto (1i, 59%), un aumento de rendimiento significativo se observa en comparación con el párrafo análogo sustituido cloruro de acilo (1h, 30%). La interacción estérica del sustituyente en la posición orto puede forzar el grupo funcional carbonilo fuera del plano, compensando así el carácter aceptor de electrones del anillo aromático. Vale la pena señalar que el cloruro de 4-bromobutirilo hace reaccionar para dar el producto deseado de 1 m con un rendimiento del 39%. Hasta donde sabemos, este es el primer protocolo para la síntesis de ynones tolerar un grupo funcional bromuro de alquilo. En ocasiones, cuando el cloruro de acilo material de partida es neutro o deficiente en electrones, impurezas alifáticos aparecen en la RMN de protón. Esto puede requerir un lavado de pentano con el fin de purificar adicionalmente el producto. Mientras sea posible, no es económico para llevar a cabo el lavado de pentano durante la primera etapa de purificación sInce pentano es costoso en comparación con hexanos. Completando la purificación secundaria por separado en una escala más pequeña tal como una columna pipeta Pasteur reduce significativamente la cantidad de pentano necesario. La Figura 3 ilustra el efecto de la identidad de la sal alkynyltrifluoroborate en el rendimiento de la reacción. En general, los derivados de sal de cojinete sustituyentes donadores de electrones del fenilacetileno trifluoroborato en el anillo aromático se hacen reaccionar con cloruros de acilo aromáticos y alifáticos para producir los ynones deseados en rendimientos de buenos a excelentes (2a-c, 3a-c). Sales de alkynyltrifluoroborate alifáticos demostraron ser sustratos menos reactivos. Rendimientos modestos se han obtenido cuando hexynyl- y sales cyclopentylethynyltrifluoroborate se hicieron reaccionar con derivados ricos en electrones de cloruro de benzoilo (4a, 5a). En conclusión, un nuevo método para la preparación of ynones de cloruros de acilo y sales de potasio alkynyltrifluoroborate se ha desarrollado. Los rendimientos obtenidos para la síntesis de ynones por este rango método de modesto a excelente dependiendo de la naturaleza del cloruro de acilo y trifluoroborato materiales de partida. En general aquellos materiales de partida que llevan sustituyentes donadores de electrones se someten a la reacción más fácilmente que los materiales de partida que tienen grupos funcionales neutros y aceptores de electrones. El valor de este enfoque radica en la simplicidad y grupo funcional tolerancia operativa del método. Esto, la reacción de un solo recipiente sencillo procede rápidamente a temperatura ambiente en presencia de tricloruro de boro sin exclusión de aire y humedad. Este método conveniente se puede emplear en la preparación de ynones en modesta a los excelentes rendimientos de una variedad de cloruros de acilo y sales alkynyltrifluoroborate.

The intention of this video is to demonstrate a straightforward approach for the preparation of compounds containing an ynone functional group from convenient starting materials. Ynones are valuable building blocks in organic chemistry that have been shown to have biomedical and material significance. Ynones are precursors to valuable organic functional groups including pyrimidines,1,2 quinolones,3 furans,4 pyrazoles,5,6 flavones,7 oximes,8 and chiral propargylic alcohols.9-11 A more convenient method for the preparation of ynones has been sought as a result of the drawbacks of traditional methods including poor functional group tolerance and tedious synthetic routes.
The reaction of metal12,13 and metalloid14 acetylides with acyl chlorides is one common route for the preparation of ynones. Alternatively, the synthesis of ynones from acyl chloride can be achieved via two-step procedures using Weinreb amides and organolithium or Grignard reagents.15 Another prevalent approach includes the addition of organolithium or Grignard reagents to an aldehyde, which is followed by the oxidation of a secondary alcohol to the corresponding ketone.16-19 Poor functional group tolerance of metal acetylides and the need to purify synthetic intermediates after each step are main deficiencies of the aforementioned methods. Transition-metal-catalyzed carbonylative couplings have recently emerged as an alternative approach for the preparation of ynones.20-22 Unfortunately, in addition to cost and toxicity associated with transition metals, metal-catalyzed carbonylative reactions often require elevated CO pressures and suffer from the presence of an undesired Sonogashira coupling byproduct. Given their utility in organic synthesis as well as the drawbacks associated with traditional synthetic methods, the development of a more straightforward method for the preparation of ynones is appealing.
Potassium organotrifluoroborate salts have recently emerged as versatile reagents in organic synthesis. Advantages including ease of preparation,23 inherent stability, low toxicity, and good functional group tolerance have made organotrifluoroborate salts attractive synthetic reagents.24-27 Organotrifluoroborate salts have been used primarily as a bench-stable equivalent of boronic acids for palladium-catalyzed Suzuki-Miyaura coupling.26 Recently, following a seminal work by Matteson and co-workers,28 Bode, Molander and others have highlighted the utility of organotrifluoroborates as reagents in non-metal catalyzed reactions.29-33 The field of transition-metal-free reactions of trifluoroborates is still in its infancy stage. Given the great potential for use of organotrifluoroborate salts in non-metal catalyzed organic synthesis, we sought to develop a novel method for the preparation of ynones from acyl chlorides and alkynyltrifluoroborate salts.

<table><tbody><tr><td>Sonicator</td><td>VGT</td><td>1860QT</td><td>Ultrasonic cleaner. Similar sonication devices may be used.</td></tr><tr><td>Dichloromethane</td><td>Sigma</td><td>270997</td><td>Anhydrous</td></tr><tr><td>Boron trichloride solution&amp;nbsp;</td><td>Sigma</td><td>178934</td><td>1 M solution in DCM</td></tr><tr><td>Acyl chloride</td><td>Sigma</td><td>Various</td><td>Acyl chlorides from other suppliers such as Alfa Aesar may be used. Caution: refer to MSDS for safety information.</td></tr><tr><td>Potassium alkynyltrifluoroborate salt</td><td>N/A</td><td>N/A</td><td>Synthesized&lt;sup&gt;23 &lt;/sup&gt;from terminal alkyne</td></tr><tr><td>Ethyl acetate</td><td>ACP</td><td>E-2000</td><td>ACS grade</td></tr><tr><td>Hexanes</td><td>ACP</td><td>H-3500</td><td>ACS grade</td></tr><tr><td>Pentane</td><td>Sigma</td><td>236705</td><td>Anhydrous</td></tr><tr><td>Magnesium sulfate</td><td>Sigma</td><td>M7506</td><td></td></tr><tr><td>Filter paper</td><td>Whatman</td><td>1093 126</td><td>Student grade. This speceific variety is not necessary.</td></tr><tr><td>Silica Gel 60</td><td>EMD</td><td>1.11567.9026</td><td>Particle size 0.040-0.063</td></tr></tbody></table>

metal-free synthesis of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts

Ynones are a valuable functional group and building block in organic synthesis. Ynones serve as a precursor to many important organic functional groups and scaffolds. Traditional methods for the preparation of ynones are associated with drawbacks including harsh conditions, multiple purification steps, and the presence of unwanted byproducts. An alternative method for the straightforward preparation of ynones from acyl chlorides and potassium alkynyltrifluoroborate salts is described herein. The adoption of organotrifluoroborate salts as an alternative to organometallic reagents for the formation of new carbon-carbon bonds has a number of advantages. Potassium organotrifluoroborate salts are shelf stable, have good functional group tolerance, low toxicity, and a wide variety are straightforward to prepare. The title reaction proceeds rapidly at ambient temperature in the presence of a Lewis acid without the exclusion of air and moisture. Fair to excellent yields may be obtained via reaction of various aryl and alkyl acid chlorides with alkynyltrifluoroborate salts in the presence of boron trichloride.

Los esfuerzos iniciales se centraron alrededor de la preparación de ynone 1a de trifluoroborato fenilacetileno S1 y cloruro de benzoilo (Figura 1). La Tabla 1 ilustra los pasos de optimización desempeñadas incluida la detección de varios ácidos de Lewis, disolventes, así como el examen del efecto del agua sobre la reacción de . A continuación, el ámbito de aplicación de la reacción ha sido explorado por la presentación de trifluoroborato fenilacetileno a las condiciones optimizadas en la presencia de una variedad de cloruros de acilo (Figura 2). Modest a excelentes rendimientos se pueden obtener dependiendo de la naturaleza del sustrato cloruro de acilo. El alcance de la reacción adicional se ha evaluado a través de la preparación de varios ejemplos adicionales de sales de alkynyltrifluoroborate. La figura 3 ilustra ejemplos seleccionados de otras sales alkynyltrifluoroborate que se pueden emplear en la preparación de ynones en las condiciones desarrolladas. Los derivados de phenylacetylene electrones rodamiento trifluoroborato sustituyentes donantes que ofrecen los productos ynone correspondientes en buenos a excelentes rendimientos mientras que los derivados alifáticos de sales alkynyltrifluoroborate demostraron ser poco menos reactivos que ofrezcan rendimientos modestos. <img alt="Figura 1" src="/files/ftp_upload/52401/52401fig1highres.jpg" /> Figura 1: Preparación de Ynone 1a de trifluoroborato fenilacetileno S1 y cloruro de benzoilo Esquema que ilustra las condiciones para la preparación de ynone 1a incluyendo la formación de la dicloroborano intermedio reactivo.. <img alt="Figura 2" src="/files/ftp_upload/52401/52401fig2highres.jpg" /> Figura 2:. Representante 1 H espectro de RMN de ynone 1a desplazamientos químicos y las integraciones relativas de protones característicos están marcados. Figura 3:. Representante 13 C espectro de RMN de ynone 1a desplazamientos químicos de los carbonos característicos están etiquetados. <img alt="Figura 4" src="/files/ftp_upload/52401/52401fig4highres.jpg" /> Figura 4:. Espectro HRMS Representante de ynone 1a obtenida a través de la ionización química a presión atmosférica El valor m / z medida del [M + H] + iones son declarados. <img alt="Figura 5" src="/files/ftp_upload/52401/52401fig5highres.jpg" /> Figura 5: Reacciones de sal phenylacetylenetrifluoroborate S1 con cloruros de acilo Estructuras y de los rendimientos de los productos producidos por la variación de la identidad.del material de partida cloruro de acilo se ilustran. Las reacciones se realizaron con 1 equiv de cloruro de acilo, 1,5 equiv S1 phenylacetylenetrifluoroborate potasio, y tricloruro de boro 1,5 equiv. <img alt="Figura 6" src="/files/ftp_upload/52401/52401fig6highres.jpg" /> Figura 6:. Reacciones de varios alkynyltrifluoroborates con cloruros de acilo Estructuras y los rendimientos para los productos producidos por la variación de la identidad del material de partida se ilustra alkynyltrifluoroborate. Las reacciones se realizaron con 1 equiv de cloruro de acilo, 2,5 equiv sal de potasio organotrifluoroborate y tricloruro de boro 2,5 equiv. <table border="0" cellpadding="0" cellspacing="0"><tbody><tr><td> Entrada </td><td> Ácido de Lewis </td><td> Ácido de Lewis (equiv) </td><td> Condiciones </td><td> Rendimiento (%) </td></tr><tr><td> 1 b &lt;/ Sup&gt; </td><td> SiO 2 </td><td> 16.5 </td><td> CH 2 Cl 2 </td><td> 0 </td></tr><tr><td> 2 </td><td> SiCl4 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> rastro </td></tr><tr><td> 3 </td><td> BF3 · OEt 2 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> rastro </td></tr><tr><td> 4 b </td><td> FeCl3 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> 24 </td></tr><tr><td> 5 c </td><td> AlCl3 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> 62 </td></tr><tr><td> 6 d </td><td> AlCl3 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> 66 </td></tr><tr><td> 7 e </td><td> AlCl3 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> 60 </td></tr><tr><td> 8 </td><td> AlCl3 </sub&gt; </td><td> 1 </td><td> THF </td><td> rastro </td></tr><tr><td> 9 </td><td> AlCl3 </td><td> 1 </td><td> tolueno </td><td> rastro </td></tr><tr><td> 10 </td><td> AlCl3 </td><td> 2 </td><td> ClCH2 CH 2 Cl </td><td> 33 </td></tr><tr><td> 11 </td><td> AlCl3 </td><td> 1 </td><td> DMSO </td><td> rastro </td></tr><tr><td> 12 </td><td> AlCl3 </td><td> 2 </td><td> acetonitrilo </td><td> rastro </td></tr><tr><td> 13 </td><td> AlCl3 · 6H 2 O </td><td> 1 </td><td> CH 2 Cl 2 </td><td> 0 </td></tr><tr><td> 14 b </td><td> BCl3 </td><td> 1.5 </td><td> CH 2 Cl 2 </td><td> 67 </td></tr><tr><td> 15 </td><td> BBr 3 </td><td> 1 </td><td> CH 2 Cl 2 </td><td> 20 </td></tr></tbody></table><strong&gt; Tabla 1:. Optimización de las condiciones para la preparación de ynone 1a un rendimiento de producto 1a en la variación de condiciones de reacción y el catalizador ácido de Lewis. A las reacciones se realizaron con cloruro de benzoilo y 1 equiv 1 equiv phenylacetylenetrifluoroborate de potasio S1. B 1.5 equiv S1. C condiciones anhidras. D La reacción se llevó a cabo en material de vidrio no se secó bajo aire. E condiciones anhidras + 1 l de agua.

Watch this Scientific Journal Video about Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts at JoVE.com

Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

The goal of this manuscript is to demonstrate a straightforward method for the preparation of ynones from acyl chloride and potassium alkynyltrifluoroborate salt starting materials. The one-pot reaction proceeds rapidly in the presence of boron trichloride without exclusion of air and moisture.

Sin metal Síntesis de Ynones de Acil cloruros y potasio Alkynyltrifluoroborate Sales

Ynones are a valuable functional group and building block in organic synthesis. Ynones serve as a precursor to many important organic functional groups ...

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11.1K vistas.  University of Ontario Institute of Technology. The goal of this manuscript is to demonstrate a straightforward method for the preparation of ynones from acyl chloride and potassium alkynyltrifluoroborate salt starting materials. The one-pot reaction proceeds rapidly in the presence of boron trichloride without exclusion of air and moisture.

Video: Metal-free Synthesis of Ynones from Acyl Chlorides and Potassium Alkynyltrifluoroborate Salts

Synthesis of Hypervalent Iodonium Alkynyl Triflates for the Application of Generating Cyanocarbenes

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent reactions with azides to form cyanocarbene intermediates. The synthesis of hypervalent iodonium alkynyl triflates can be facile, but difficulties stem from their isolation and reactivity. In particular, the necessity to use filtration under inert atmosphere at -45 &deg;C for some HIATs requires special care and equipment. Once isolated, the compounds can be stored and used in reactions with azides to form cyanocarbene intermediates. 
The evidence for cyanocarbene generation is shown by visible extrusion of dinitrogen as well as the characterization of products that occur from O-H insertion, sulfoxide complexation, and cyclopropanation. A side reaction of the cyanocarbene formation is the generation of a vinylidene-carbene and the conditions to control this process are discussed. There is also potential to form a hypervalent iodonium alkenyl triflate and the means of isolation and control of its generation are provided. The O-H insertion reaction involves using a HIAT, sodium azide or tetrabutylammonium azide, and methanol as solvent/substrate. The sulfoxide complexation reaction uses a HIAT, sodium azide or tetrabutylammonium azide, and dimethyl sulfoxide as solvent. The cyclopropanations can be performed with or without the use of solvent. The azide source must be tetrabutylammonium azide and the substrate shown is styrene.

Herein is described the synthesis, isolation, and reactions of hypervalent iodonium alkynyl triflates (HIATs) with azides to generate cyanocarbenes. The procedures will involve air-sensitive and cryogen techniques, including cold filtration under an inert atmosphere. Handling and safety of the synthesized compounds will also be discussed.

Síntesis de hipervalente iodonio Alquinilo triflatos para la Aplicación de Generación Cyanocarbenes

The procedures described in this article involve the synthesis and isolation of hypervalent iodonium alkynyl triflates (HIATs) and their subsequent ...

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Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of trifluoromethoxylated aromatic compounds remains a formidable challenge in organic synthesis. Conventional approaches often suffer from poor substrate scope, or require use of highly toxic, difficult-to-handle, and/or thermally labile reagents. Herein, we report a user-friendly protocol for the synthesis of methyl 4-acetamido-3-(trifluoromethoxy)benzoate using 1-trifluoromethyl-1,2-benziodoxol-3(1H)-one (Togni reagent II). Treating methyl 4-(N-hydroxyacetamido)benzoate (1a) with Togni reagent II in the presence of a catalytic amount of cesium carbonate (Cs2CO3) in chloroform at RT afforded methyl 4-(N-(trifluoromethoxy)acetamido)benzoate (2a). This intermediate was then converted to the final product methyl 4-acetamido-3-(trifluoromethoxy)benzoate (3a) in nitromethane at 120 &#176;C. This procedure is general and can be applied to the synthesis of a broad spectrum of ortho-trifluoromethoxylated aniline derivatives, which could serve as useful synthetic building blocks for the discovery and development of new pharmaceuticals, agrochemicals, and functional materials.

Protocol for the Synthesis of Ortho-trifluoromethoxylated Aniline Derivatives

An operationally simple procedure for the synthesis of ortho-trifluoromethoxylated aniline derivatives via a two-step sequence of O-trifluoromethylation of N-aryl-N-hydroxyacetamide followed by thermally induced intramolecular OCF3-migration is reported.

Protocolo para la Síntesis de<em&gt; Ortho</em&gt; derivados de anilina -trifluoromethoxylated

Molecules bearing trifluoromethoxy (OCF3) group often show desired pharmacological and biological properties. However, facile synthesis of ...

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. Recently, we have developed a two-step strategy for ketone enolate umpolung that has enabled the development of methods for chlorination, azidation, and amination using azoles. In addition, we have developed C-C bond&#8211;forming arylation and allylation reactions. At the heart of these methods is the preparation of the intermediate and highly reactive enolonium species prior to addition of a reactive nucleophile. This strategy is thus reminiscent of the preparation and use of metal enolates in classical synthetic chemistry. This strategy allows the use of nucleophiles that would otherwise be incompatible with the strongly oxidizing hypervalent iodine reagents. In this paper we present a detailed protocol for chlorination, azidation, N-heteroarylation, arylation, and allylation. The products include motifs prevalent in medicinally active products. This article will greatly assist others in using these methods.

A two step one-pot protocol for the umpolung of ketone enolates to enolonium species and addition of a nucleophile to the &#945;-position is described. Nucleophiles include chloride, azide, azoles, allyl-silanes, and aromatic compounds.

Un protocolo de dos etapas para funcionalización de Umpolung de cetonas vía Enolonium especies

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. ...

Application of Elemental Lanthanides in the Selective C-F Activation of Trifluoromethylated Benzofulvenes Providing Access to Various Difluoroalkenes

The selective activation of one carbon-fluorine bond in polyfluorinated aromatic molecules or in trifluoromethyl-containing substrates offers the possibility of accessing unique fluorine-containing molecules, which are difficult to obtain by other synthetic pathways. Among various metals, which can undergo C-F activation, lanthanides (Ln) are good candidates as they form strong Ln-F bonds. Lanthanide metals are strong reducing agents with a redox potential Ln3+/Ln&#160;of approximately -2.3 V, which is comparable to the value of the Mg2+/Mg&#160;redox couple. In addition, lanthanide metals display a promising functional group tolerance and their reactivity can vary along the lanthanide series, making them suitable reagents for fine-tuning reaction conditions in organic and organometallic transformations. However, due to their oxophilicity, lanthanides react readily with oxygen and water and therefore require special conditions for storage, handling, preparation, and activation. These factors have limited a more widespread use in organic synthesis. We herein present how dysprosium metal - and by analogy all lanthanide metals - can be freshly prepared under anhydrous conditions using glovebox and Schlenk techniques. The freshly filed metal, in combination with aluminum chloride, initiates the selective C-F activation in trifluoromethylated benzofulvenes. The resulting reaction intermediates react with nitroalkenes to obtain a new family of difluoroalkenes.

This protocol describes the preparation of elemental lanthanides under inert atmosphere and their application in a selective C-F activation process involving trifluoromethylated benzofulvenes.

Aplicación de lantánidos Elemental en la activación de C-F selectiva de Trifluoromethylated Benzofulvenes acceso a varios Difluoroalkenes

The selective activation of one carbon-fluorine bond in polyfluorinated aromatic molecules or in trifluoromethyl-containing substrates offers the ...

Chemoselective Preparation of 1-Iodoalkynes, 1,2-Diiodoalkenes, and 1,1,2-Triiodoalkenes Based on the Oxidative Iodination of Terminal Alkynes

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and 1-methyl-4-(1,2,2-triiodovinyl)benzene as representative examples for the practical chemoselective preparation of 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes from the chemoselective iodination of terminal alkynes mediated by hypervalent-iodine reagents. The chemoselectivity was confirmed by using p-tolylethyne as a model substrate to screen a variety of iodine sources and/or the hypervalent-iodine reagents. A combination of tetrabutylammonium iodide (TBAI) and (diacetoxyiodo)benzene (PIDA) selectively generates 1-iodoalkynes, while a combination of KI and PIDA generates 1,2-diiodoalkenes. A one-pot synthesis based on both TBAI-PIDA and KI-PIDA yields the corresponding 1,1,2-triiodoalkenes. These protocols were subsequently applied to the synthesis of synthetically important aromatic and aliphatic 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes, which were obtained in good yield with excellent chemoselectivity.

Herein, detailed protocols for the oxidative iodination of terminal alkynes using hypervalent-iodine reagents are presented, which chemoselectively afford 1-iodoalkynes, 1,2-diiodoalkenes, and 1,1,2-triiodoalkenes.

Preparación estereoselectiva de 1 Iodoalkynes, 1, 2-Diiodoalkenes y 1.1.2-Triiodoalkenes basado en la yodación oxidativa de alquinos terminales

We present the chemoselective synthesis of 1-(iodoethynyl)-4-methylbenzene, 1-(1,2-diiodovinyl)-4-methylbenzene, and ...

Isolating Free Carbenes, their Mixed Dimers and Organic Radicals

Protocols for the isolation of the commonly employed cyclic (alkyl)(amino) carbene (CAAC) and N-heterocyclic carbene (NHC) are reported. Furthermore, the synthesis of their mixed CAAC&#8211;NHC &#8220;Wanzlick&#8221; dimer and the synthesis of the related stable organic &#8220;olefin&#8221; radical are presented. The main goal of this manuscript is to give a detailed and general protocol for the synthetic chemist of any skill level on how to prepare free heterocyclic carbenes by deprotonation using filter cannulas. Due to the air-sensitivity of the synthesized compounds, all experiments are performed under inert atmosphere using either Schlenk technique or a dinitrogen filled glovebox. Controlling Wanzlick&#8217;s equilibrium (i.e., the dimerization of free carbenes), is a crucial requirement for the application of free carbenes in coordination chemistry or organic synthesis. Thus, we elaborate on the specific electronic and steric requirements favoring the formation of dimers, heterodimers, or monomers. We will show how proton catalysis allows for the formation of dimers, and how the electronic structure of carbenes and their dimers affects the reactivity with either moisture or air. The structural identity of the reported compounds is discussed based on their NMR spectra.

We present protocols for the isolation of stable heterocyclic carbenes. The synthesis of a cyclic (alkyl)(amino) carbene (CAAC) and an N-heterocyclic carbene (NHC) is demonstrated using filter cannulas and Schlenk technique. We furthermore present the synthesis of the related oxygen-sensitive, electron-rich mixed &#8220;Wanzlick dimer&#8221; and the reduced stable organic radical.

Aislamiento de carbenos libre mixto dímeros y sus radicales orgánicos

Protocols for the isolation of the commonly employed cyclic (alkyl)(amino) carbene (CAAC) and N-heterocyclic carbene (NHC) are reported. Furthermore, the ...

Efficient Synthesis of All-Carbon Quaternary Centers via the Conjugate Addition of Functionalized Monoorganozinc Bromides

The conjugate addition of organometallic reagents to &#945;,&#946;-unsaturated carbonyls represents an important method to generate C&#8211;C bonds in the preparation of all-carbon quaternary centers. Though conjugate additions of organometallic reagents are typically performed utilizing highly reactive organolithium or Grignard reagents, organozinc reagents have garnered attention for their enhanced chemoselectivity and mild reactivity. Despite numerous recent advances with more reactive diorganozinc and mixed diorganozinc reagents, the generation of all-carbon quaternary centers via the conjugate addition of functionalized monoorganozinc reagents remains a challenge. This protocol details a convenient and mild &#8220;one-pot&#8221; preparation and copper mediated conjugate addition of functionalized monoorganozinc bromides to cyclic &#945;,&#946;-unsaturated carbonyls to afford a broad scope of all-carbon quaternary centers in generally excellent yield and diastereoselectivity. Key to the development of this technology is the utilization of DMA as a reaction solvent with TMSCl as a Lewis acid. Notable advantages to this methodology include the operational simplicity of the organozinc reagent preparation afforded by the utilization of DMA as a solvent, as well as an efficient conjugate addition mediated by various Cu(I) and Cu(II) salts. Moreover, an intermediate silyl enol ether can be isolated utilizing a modified workup procedure. The substrate scope is limited to cyclic unsaturated ketones, and the conjugate addition is impeded by stabilized (e.g., allyl, enolate, homoenolate) and sterically encumbered (e.g., neopentyl, o-aryl) monoorganozinc reagents. Conjugate additions to five- and seven-membered rings were effective, albeit in lower yields compared with six-membered ring substrates.

A simple and practical protocol for the efficient conjugate addition of functionalized monoorganozinc bromides to cyclic &#945;,&#946;-unsaturated carbonyls to furnish all-carbon quaternary centers was developed.

Síntesis eficiente de los centros cuaternarios de carbono a través de la adición conjugada de bromuros Monoorganozinc funcionalizados

The conjugate addition of organometallic reagents to &#945;,&#946;-unsaturated carbonyls represents an important method to generate C&#8211;C bonds in the ...

Acidity of 1-Alkynes

<h4></h4>
The acidic strength of hydrocarbons follows the order: Alkynes &#62; Alkenes &#62; Alkanes. The strength of an acid is commonly expressed in units of pKa &#8212; the lower the pKa, the stronger the acid. Among the hydrocarbons, terminal alkynes have lower pKa values and are, therefore, more acidic. For example, the pKa values for ethane, ethene, and acetylene are 51, 44, and 25, respectively, as shown here.
<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure1left" src="/files/ftp_upload/11833/11833_PT_Figure_1_left.svg" style="text-align: center; height: 75px;" /> 
			Ethane 
			(pKa&#160;= 51)</td>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure1middle" src="/files/ftp_upload/11833/11833_PT_Figure_1_Middle.svg" style="text-align: center; height: 50px;" /> 
			 
			Ethene 
			(pKa&#160;= 44)</td>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;">
			
			<img alt="Figure1right" src="/files/ftp_upload/11833/11833_PT_Figure_1_Right.svg" style="text-align: center; height: 20px;" /> 
			 
			&#160;
			Ethyne 
			(pKa&#160;= 25)
			</td>
		</tr>
	</tbody>
</table>
With a pKa difference of 26 units, acetylene is 1026 times more acidic than ethane. Similarly, a difference of 19 pKa units makes it 1019 times stronger than ethene.
<h4>Hybridization effect</h4>
The pronounced increase in the acidity of terminal alkynes relative to the other hydrocarbons can be explained by considering the stability of the corresponding carbanions formed by deprotonation. Note that, in the nomenclature of organic compounds, the suffix &#34;-ide&#34; indicates that the molecule is a negatively charged ion.
<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure2top" src="/files/ftp_upload/11833/11833_PT_Figure_2_top.svg" style="text-align: center; height: 80px;" /> 
			ethanide&#160;(an alkyl anion) 
			sp3&#160;lone pair, 25% &#8220;s&#8221; character</td>
		</tr>
		<tr>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure2middle" src="/files/ftp_upload/11833/11833_PT_Figure_2_middle.svg" style="text-align: center; height: 60px;" /> 
			ethenide&#160;(a vinylic anion) 
			sp2&#160;lone pair, 33% &#8220;s&#8221; character</td>
		</tr>
		<tr>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure2bottom" src="/files/ftp_upload/11833/11833_PT_Figure_2_bottom.svg" style="text-align: center; height: 40px;" /> 
			acetylide&#160;(an acetylenic anion) 
			sp&#160;lone pair, 50% &#8220;s&#8221; character</td>
		</tr>
	</tbody>
</table>
The stability of the carbanion depends on the nature of the hybridized orbital occupied by the lone pair of electrons. As shown above, in ethane&#160;the lone pair resides in an sp3 orbital, while in ethene&#160;it occupies the sp2 orbital and an sp orbital in the case of acetylene. The sp3, sp2, and sp orbitals have 25%, 33%, and 50% &#34;s&#34; character, respectively. Since &#34;s&#34; orbitals are closer to the positively charged nucleus, a hybrid orbital with a higher &#34;s&#34; character will effectively stabilize the negative charge. Thus, the acetylide ions will be the most stable and readily formed in the presence of a suitable base.
<h4>Choosing a suitable base</h4>
In general, for a base to deprotonate an acid, the pKa of the base&#39;s conjugate acid must be at least 10 pKa units greater than that of the acid.
<img alt="Figure3" src="/files/ftp_upload/11833/11833_Figure_3v2.svg" style="text-align: center; height: 80px;" />
Terminal alkynes have a pKa of 25. Therefore, an appropriate base would be one where the conjugate acid has a pKa that is at least 35. Recall that for an acid-base reaction, the equilibrium favors the formation of weaker acids and bases from stronger acids and bases.
stronger acids + stronger bases <img alt="arrow" src="/files/ftp_upload/11833/arrow.png" style="text-align: center; height: 13px;" />weaker acids + weaker bases
With sodium amide as the base, terminal alkynes form sodium acetylide and ammonia as the conjugate acid. Since the pKa of ammonia is greater than 25, the equilibrium favors the formation of sodium acetylide, making sodium amide a strong enough base for the deprotonation reaction.
<img alt="Figure4" src="/files/ftp_upload/11833/11833_Figure_4.svg" style="text-align: center; height: 100px;" />
Apart from sodium amide, sodium hydride, butyllithium, and lithium diisopropylamide (LDA) are other commonly used bases to form acetylide ions.
<table style="margin-left: auto; margin-right: auto;">
	<tbody style="border: 1px solid black;">
		<tr>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;">
			<img alt="Figure5left" src="/files/ftp_upload/11833/11833_PT_Figure_5_left.svg" style="height: 25px;" />
			Sodium hydride
			</td>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure5middle" src="/files/ftp_upload/11833/11833_PT_Figure_5_middle.svg" style="text-align: center; height: 60px;" /> 
			Butyllithium (n-BuLi)</td>
			<td style="border-style: solid; border-color: black; color: black; text-align: center;"><img alt="Figure5right" src="/files/ftp_upload/11833/11833_PT_Figure_5_right.svg" style="text-align: center; height: 60px;" /> 
			Lithium diisopropylamide (LDA)</td>
		</tr>
	</tbody>
</table>
In the presence of sodium hydroxide as the base, terminal alkynes form sodium acetylide and water as the conjugate acid. However, since the pKa of water is less than 25, the equilibrium favors the reactants. Therefore, sodium hydroxide is not a suitable base to form acetylide ions.
<img alt="Figure6" src="/files/ftp_upload/11833/11833_Figure_6.svg" style="text-align: center; height: 110px;" />
<h4>Synthesis of organometallic reagents </h4>
The relative acidity of terminal alkynes finds application in the synthesis of organometallic compounds when treated with Grignard or organolithium reagents. These are examples of transmetalation reactions involving the transfer of a metal atom from one carbon to another, thereby forming new metal&#8211;carbon bonds. However, they can also be interpreted as acid&#8211;base reactions that favor the formation of weaker acids and bases.
<img alt="Figure7top" src="/files/ftp_upload/11833/11833_Figure_7v3.svg" style="text-align: center; height: 225px;" />
<div></div>

Acidity of Terminal Alkynes: Formation of Acetylide Anions

Acidez de los 1-alquinos


The acidic strength of hydrocarbons follows the order: Alkynes &#62; Alkenes &#62; Alkanes. The strength of an acid is commonly expressed in units of pKa ...

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Alquinos

TÉRMINOS Y CONCEPTOS CLAVES

Preparation of Alkynes: Alkylation Reaction

<h4>Introduction</h4>
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for the synthesis of longer carbon-chain alkynes. For example, treatment of 1-propyne with sodium amide followed by reaction with ethyl bromide yields 2-pentyne.
<img alt="Alkyne alkylation reaction using NaNH2 and ethyl bromide, chemical equation diagram." src="/files/ftp_upload/11834/11834_PT_Figure_1.svg" style="text-align: center; height: 50px;" data-altupdatedat="1747908711000" data-alt="Figure1">
The reaction takes place in two steps:
1. The first step is the deprotonation of the terminal alkyne by the strong base forming an acetylide ion.
<img alt="Alkyne ionization reaction equation NaNH2, diagram shows acetylene converting to acetylide ion." src="/files/ftp_upload/11834/11834_PT_Figure_2.svg" style="text-align: center; height: 50px;" data-altupdatedat="1747908711000" data-alt="Figure2">
2. The second step is a nucleophilic substitution reaction in which the acetylide ion reacts with the alkyl halide to form a new C–C bond.
<img alt="Organic reaction mechanism, Na+ and Br- ion exchange, illustrates chemical synthesis process." src="/files/ftp_upload/11834/11834_PT_Figure_3.svg" style="text-align: center; height: 50px;" data-altupdatedat="1747908711000" data-alt="Figure3">
<h4>Reaction Mechanism —SN2 pathway </h4>
Acetylide ions are strong bases and can also function as good nucleophiles. The substitution reaction follows an SN2 pathway where the nucleophilic acetylide ion attacks the electrophilic carbon of the primary alkyl halide from the backside.
<img alt="Nucleophilic substitution reaction mechanism diagram with alkynes, NaBr formation, chemical process." src="/files/ftp_upload/11834/11834_PT_Figure_4.svg" style="text-align: center; height: 250px;" data-altupdatedat="1747908711000" data-alt="Figure4">
Since this is a concerted process, the nucleophilic attack and the departure of the leaving group takes place simultaneously to form the product with an inverted stereochemistry at the reaction center.
The reaction works best with unhindered alkyl halides like methyl halide and other primary halides. With secondary and tertiary alkyl halides, acetylide ions act as strong bases, in which case E2 elimination is the preferred pathway.
<h4>Application in organic synthesis </h4>
Alkylation of simple terminal alkynes is a useful method to extend the length of the carbon chain. Acetylene, a terminal alkyne, can be converted to a higher internal alkyne by repeated alkylation as shown below:
<img alt="Alkyne chain elongation via NaNH₂, CH₃Br; reaction equation diagram for organic synthesis." src="/files/ftp_upload/11834/11834_PT_Figure_5.svg" style="text-align: center; height: 50px;" data-altupdatedat="1747908711000" data-alt="Figure5">

Preparación de alquinos: Reacción de alquilación

Introduction
Alkylation of terminal alkynes with primary alkyl halides in the presence of a strong base like sodium amide is one of the common methods for ...

Preparation of Alkynes: Dehydrohalogenation

<h4>Introduction</h4>
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ammonia. The reaction proceeds with the loss of two equivalents of hydrogen halide (HX) via two successive E2 elimination reactions.
<img alt="Chemical reaction diagram, alkyne synthesis, 2NaNH2/NH3, hydrogen elimination, organic chemistry." src="/files/ftp_upload/11835/11835_PT_Figure_1.svg" style="text-align: center; height: 200px;" data-altupdatedat="1747908711000" data-alt="Figure1">
<h4>Reaction Mechanism – E2 pathway</h4>
Vicinal dihalides
In the first elimination step, the strong base abstracts the proton from the dihalide that is oriented anti to the leaving group. Since E2 reactions follow a concerted pathway, the abstraction of a proton and departure of the halide leaving group occur simultaneously to form a haloalkene.
<img alt="Birch reduction mechanism diagram, showing electron flow in organic compound reaction." src="/files/ftp_upload/11835/11835_PT_Figure_2.svg" style="text-align: center; height: 90px;" data-altupdatedat="1747908711000" data-alt="Figure2">
In the second elimination reaction, another equivalent of the strong base reacts with the haloalkene in a similar fashion to give the desired alkyne.
<img alt="Elimination reaction mechanism diagram, E2 mechanism, showing alkene formation from alkyl halide." src="/files/ftp_upload/11835/11835_PT_Figure_3.svg" style="text-align: center; height: 90px;" data-altupdatedat="1747908711000" data-alt="Figure3">
Geminal dihalides
Likewise, geminal dihalides, when treated with two equivalents of a sodium amide, undergo double dehydrohalogenation to give alkynes.
<img alt="Alkyne formation reaction; sodium amide abstracting proton; chemical equation diagram; synthesis method." src="/files/ftp_upload/11835/11835_PT_Figure_4.svg" style="text-align: center; height: 90px;" data-altupdatedat="1747908711000" data-alt="Figure4">
<img alt="Chemical reaction mechanism, arrow-pushing diagram, alkyne formation using sodium amide." src="/files/ftp_upload/11835/11835_PT_Figure_5.svg" style="text-align: center; height: 90px;" data-altupdatedat="1747908711000" data-alt="Figure5">
Terminal dihalides 
Dehydrohalogenation of terminal dihalides yields terminal alkynes as the final product. In the presence of a strong base like sodium amide, terminal alkynes get converted to acetylide ions. In such cases, a third equivalent of the base is required to complete the dehydrohalogenation of the remaining haloalkene.
<img alt="Hofmann elimination reaction; chemical equations diagram; synthesis process using NaNH2; alkyne formation." src="/files/ftp_upload/11835/11835_PT_Figure_6.svg" style="text-align: center; height: 70px;" data-altupdatedat="1747908711000" data-alt="Figure6">
Protonation of the acetylide ions with water or an aqueous acid completes the reaction.
<img alt="Organic reaction mechanism with sodium acetylide, water; diagram illustrating nucleophilic attack." src="/files/ftp_upload/11835/11835_PT_Figure_7.svg" style="text-align: center; height: 50px;" data-altupdatedat="1747908711000" data-alt="Figure7">
<h4>Application in Organic Synthesis</h4>
Dehydrohalogenation of vicinal dihalides is a useful intermediate step in the conversion of alkenes to alkynes. For example, chlorination of 1-propene gives 1,2-dichloropropane – a vicinal dihalide, which upon double dehydrohalogenation yields 1-propyne.
<img alt="Alkene to alkyne conversion diagram; chemical reaction mechanism, dichlorination, dehydrohalogenation." src="/files/ftp_upload/11835/11835_PT_Figure_8.svg" style="text-align: center; height: 60px;" data-altupdatedat="1747908711000" data-alt="Figure8">
Similarly, alkynes can also be synthesized from ketones via dehydrohalogenation of geminal dihalides. For example, treatment of acetone with phosphorous pentachloride yields 2,2-dichloropropane – a geminal dihalide, which undergoes double dehydrohalogenation to give 1-propyne.
<img alt="Organic synthesis mechanism; ketone to alkyne via substitution and elimination; chemical reaction diagram." src="/files/ftp_upload/11835/11835_PT_Figure_9.svg" style="text-align: center; height: 80px;" data-altupdatedat="1747908711000" data-alt="Figure9">

Prepararación de alquinos: Deshidrohalogenación

Introduction
Alkynes can be prepared by dehydrohalogenation of vicinal or geminal dihalides in the presence of a strong base like sodium amide in liquid ...