This research was supported by the Bill and Linda Frost Fund.

CAUTION: Please review all relevant material safety data sheets (MSDS) before use. Follow all appropriate safety practices when using the microwave reactor including reviewing the microwave reactor protocols and the use of personal protective equipment (safety glasses, gloves, lab coat, full-length pants, closed-toe shoes). This procedure is designed to work using an aryl hydrazine and either 3-aminocrotononitrile or an &#945;-cyanoketone. The appropriate microwave vial and stir bar should be used according to the scale of the reaction as specified by the manufacturer.
1. Preparation of reaction mixture
NOTE: The following reaction between 4-fluorophenylhydrazine hydrochloride and 3-aminocrotononitrile on a 2 mmol scale is representative. The procedure is identical when substituting &#945;-cyanoketones in place of 3-aminocrotononitrile14.
<ol>
	<li>Obtain a microwave vial designed for reaction volumes of 2-5 mL that has been dried overnight in a glassware oven and add an appropriate stir bar.</li>
	<li>Add 0.325 g of 4-fluorophenylhydrazine hydrochloride (1 equiv., 2 mmol) and 0.164 g of 3-aminocrotononitrile (1 equiv., 2 mmol) to the microwave vial.</li>
	<li>Add 5 mL of 1 M HCl to make the concentration of starting reagents as 0.4 M. Using a stir plate, ensure that the heterogeneous suspension is stirred. Add additional solvent if reactants have poor solubility and the reaction mixture cannot be stirred properly. Transfer the solution to a larger vial if necessary, to avoid exceeding the recommend solvent volume as specified by the microwave reactor operating manual.</li>
</ol>
2. Heating the reaction in the microwave reactor
<ol>
	<li>Seal the microwave vial with a microwave vial cap using the appropriate crimper tool.</li>
	<li>Place the vial in the microwave reactor. Program the microwave settings for time (10 min), temperature (150 &#176;C), and absorption (Very High). 
	CAUTION: Pay attention to the reactor pressure during the heating phase. A sudden drop in pressure may indicate a leak and/or vessel failure.</li>
	<li>Once the reaction has cooled (&#60; 40 &#176;C), remove the vial from the microwave reactor.</li>
	<li>Remove the cap using an appropriate decapper tool.</li>
</ol>
3. Isolation of the product by vacuum filtration
<ol>
	<li>In a well ventilated fume hood, clamp the microwave vial over a stir plate.</li>
	<li>Add 2 mL of 10% NaOH with stirring to make the solution alkaline and cause immediate precipitation of product. The pH of the solution should be &#62;10 as indicated by pH paper. Sonication and scraping the vial with a spatula can aid with mixing and dislodging product from the vessel walls. 
	NOTE: Some products oil out of the alkaline solution. If this occurs, transfer the solution with the aid of ~20 mL of deionized water to a separatory funnel and extract 3x with dichloromethane or ethyl acetate. Dry the combined organic layers and evaporate to obtain the product.</li>
	<li>Set up a vacuum filtration apparatus to isolate solid product precipitate. Use deionized water to rinse any remaining product from the microwave vial and wash the isolated product.</li>
	<li>Allow the product to dry overnight on the bench top or in a desiccator. Isolated yields are typically in the 70-90% range14.</li>
	<li>Obtain a 1H NMR spectrum in CDCl3 to confirm product identity and purity.</li>
</ol>

<ol>
	<li>Gradler, U., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fragment-based+discovery+of+focal+adhesion+kinase+inhibitors.">Fragment-based discovery of focal adhesion kinase inhibitors.</a> Bioorganic &amp; Medicinal Chemistry Letters. 23 (19), 5401-5409 (2013).</li><li>Chandak, N., Kumar, S., Kumar, P., Sharma, C., Aneja, K. R., Sharma, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exploration+of+antimicrobial+potential+of+pyrazolo[3,4-b]pyridine+scaffold+bearing+benzenesulfonamide+and+trifluoromethyl+moieties.">Exploration of antimicrobial potential of pyrazolo[3,4-b]pyridine scaffold bearing benzenesulfonamide and trifluoromethyl moieties.</a> Medicinal Chemistry Research. 22 (11), 5490-5503 (2013).</li><li>Huo, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+and+biological+activity+of+novel+N-(3-furan-2-yl-1-phenyl-1H-pyrazol-5-yl)+amides+derivatives.">Synthesis and biological activity of novel N-(3-furan-2-yl-1-phenyl-1H-pyrazol-5-yl) amides derivatives.</a> Chinese Chemical Letters. 27 (9), 1547-1550 (2016).</li><li>Anand, D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antileishmanial+activity+of+pyrazolopyridine+derivatives+and+their+potential+as+an+adjunct+therapy+with+miltefosine.">Antileishmanial activity of pyrazolopyridine derivatives and their potential as an adjunct therapy with miltefosine.</a> Journal of Medicinal Chemistry. 60 (3), 1041-1059 (2017).</li><li>Eldehna, W. M., El-Naggar, D. H., Hamed, A. R., Ibrahim, H. S., Ghabbour, H. A., Abdel-Aziz, H. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=One-pot+three-component+synthesis+of+novel+spirooxindoles+with+potential+cytotoxic+activity+against+triple-negative+breast+cancer+MDA-MB-231+cells.">One-pot three-component synthesis of novel spirooxindoles with potential cytotoxic activity against triple-negative breast cancer MDA-MB-231 cells.</a> Journal of Enzyme Inhibition and Medicinal Chemistry. 33 (1), 309-318 (2017).</li><li>Briebenow, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+optimization+of+substituted+5-aminopyrazoles+as+potent+and+selective+adenosine+A1+receptor+antagonists.">Identification and optimization of substituted 5-aminopyrazoles as potent and selective adenosine A1 receptor antagonists.</a> Bioorganic &amp; Medicinal Chemistry Letters. 20 (19), 5891-5894 (2010).</li><li>Marinozzi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pyrazole[3,4-e][1,4]thiazepin-7-one+derivatives+as+a+novel+class+of+Farnesoid+X+Receptor+(FXR)+agonists.">Pyrazole[3,4-e][1,4]thiazepin-7-one derivatives as a novel class of Farnesoid X Receptor (FXR) agonists.</a> Bioorganic &amp; Medicinal Chemistry. 20 (11), 3429-3445 (2012).</li><li>Ochiai, H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Discovery+of+new+orally+available+active+phosphodiesterase+inhibitors.">Discovery of new orally available active phosphodiesterase inhibitors.</a> Chemical and Pharmaceutical Bulletin. 52 (9), 1098-1104 (2004).</li><li>Ganesan, A., Heathcock, C. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Synthesis+of+unsymmetrical+pyrazines+by+reaction+of+an+oxadiazinone+with+enamines.">Synthesis of unsymmetrical pyrazines by reaction of an oxadiazinone with enamines.</a> Journal of Organic Chemistry. 58 (22), 6155-6157 (1993).</li><li>Sumesh, R. V., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multicomponent+dipolar+cycloaddition+strategy:+combinatorial+synthesis+of+novel+spiro-tethered+pyrazolo[3,4-b]quinoline+hybrid+heterocycles.">Multicomponent dipolar cycloaddition strategy: combinatorial synthesis of novel spiro-tethered pyrazolo[3,4-b]quinoline hybrid heterocycles.</a> ACS Combinatorial Science. 18 (5), 262-270 (2016).</li><li>Bagley, M. C., Davis, T., Dix, M. C., Widdowson, C. S., Kipling, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave-assisted+synthesis+of+N-pyrazole+ureas+and+the+p38&#945;+inhibitor+BIRB+796+for+study+into+accelerated+cell+ageing.">Microwave-assisted synthesis of N-pyrazole ureas and the p38&#945; inhibitor BIRB 796 for study into accelerated cell ageing.</a> Organic &amp; Biomolecular Chemistry. 4 (22), 4158-4164 (2006).</li><li>Su, W., Lin, T., Cheng, K., Sung, K., Lin, S., Wong, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+efficient+on-pot+synthesis+of+N-(1,3-diphenyl-1H-pyrazol-5-yl)amides.">An efficient on-pot synthesis of N-(1,3-diphenyl-1H-pyrazol-5-yl)amides.</a> Journal of Heterocyclic Chemistry. 47 (4), 831-837 (2010).</li><li>Eagon, S., Anderson, M. O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave-assisted+synthesis+of+tetrahydro-&#946;-carbolines+and+&#946;-carbolines.">Microwave-assisted synthesis of tetrahydro-&#946;-carbolines and &#946;-carbolines.</a> European Journal of Organic Chemistry. (8), 1653-1665 (2014).</li><li>Everson, N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microwave+synthesis+of+1-aryl-1H-pyrazole-5-amines.">Microwave synthesis of 1-aryl-1H-pyrazole-5-amines.</a> Tetrahedron Letters. 60 (1), 72-74 (2019).</li></ol>

The authors have nothing to disclose.

A number of 1-aryl-1H-pyrazole-5-amines were prepared by combining an &#945;-cyanoketone or 3-aminocrotonitile with an aryl hydrazine in 1 M HCl and heating the solution to 150 &#176;C in a microwave reactor. Nearly all compounds were synthesized in 10-15 min, with the slowest substrate requiring 35 min of heating14. The use of water as the solvent allows for rapid heating of the solution and minimizes the use of hazardous organic solvents.
Higher temperature a...

The impetus to create a streamlined synthesis of 1-aryl-1H-pyrazole-5-amines is due to the myriad of applications of these small molecules. They appear in kinase inhibitors1, antibiotics2, pesticides3, and among many other biologically active compounds4,5. Synthetic schemes for these compounds are abundant, but most involve complex isolation and purification techniques. A common method involves the reflux of aryl hydrazine and 3-aminocrotononitrile in either alcoholic or aqueous solutions followed by a subsequent purification via chromatography and/or recrystallization6,7,8,9,10. A handful of isolated reports have detailed the synthesis of these compounds using microwave radiation, but all required extensive heating time and offered little advantage when compared to other previously reported methods11,12.
Despite their utility, there are a limited number of 1-aryl-1H-pyrazole-5-amines available from commercial vendors. We recently had success preparing nitrogen heterocycles using a microwave reactor13 and decided to investigate a related methodology for pyrazole-5-amine analogs. In this paper, we detail our procedure to prepare 1-aryl-1H-pyrazole-5-amines by reacting an aryl hydrazine with either 3-aminocrotononitrile or an &#945;-cyanoketone in 1 M HCl under microwave radiation. The advantages of this procedure include a short reaction time and the ability to incorporate a variety of functional groups including halides, nitriles, phenols, sulfones and nitro groups14.

<table><tbody><tr><td>2-5mL Microwave vial set</td><td>Chemglass</td><td>CG-4920-01&amp;nbsp;</td><td>Set includes appropriate stir bars and 20mm aluminum seals</td></tr><tr><td>Biotage Initiator+ microwave</td><td>Biotage</td><td>356007</td><td>Includes crimper and decapper tool.</td></tr><tr><td>Sonicator</td><td>Kendal</td><td>Ultrasonic Cleaner GB-928</td><td></td></tr><tr><td>Glassware oven</td><td>Quincy Lab</td><td>20GC</td><td></td></tr><tr><td>4-Fluorophenylhydrazine hydrochloride</td><td>Fisher</td><td>AC119590100</td><td></td></tr><tr><td>3-Aminocrotonitrile</td><td>Fisher</td><td>AC152451000</td><td></td></tr><tr><td>CDCl3</td><td>Cambridge Labs</td><td>DLM-7-100</td><td>99.8% D</td></tr><tr><td>Hydrochloric acid, concentrated</td><td>Fisher</td><td>A144SI-212</td><td>Used to prepare 1 M HCl solution</td></tr><tr><td>Sodium hydroxide pellets</td><td>Fisher</td><td>S318-100</td><td>Used to prepare 10% NaOH solution</td></tr></tbody></table>

microwave-assisted preparation of 1-aryl-1h-pyrazole-5-amines

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it efficient in both time and resources and utilizes water as the solvent. 3-Aminocrotononitrile or an appropriate &#945;-cyanoketone is combined with an aryl hydrazine and dissolved in 1 M HCl. The mixture is then heated in a microwave reactor at 150 &#176;C, typically for 10-15 min. The product can be readily obtained by basifying the solution with 10% NaOH and isolating the desired compound with a simple vacuum filtration. The use of water as a solvent in this reaction lends to its ease and utility in production, and this method is easily reproducible with a variety of functional groups. Typical isolated yields range from 70-90%, and reactions can be performed on the milligram to gram scale with little to no change in observed yields. Some of the applications of these molecules and their derivatives include pesticides, anti-malarials, and chemotherapeutics, among many others.

In this demonstration, 3-aminocrotononitrile and 4-fluorophenylhydrazine hydrochloride were reacted to produce 1-(4-fluorophenyl)-3-methyl-1H-pyrazol-5-amine (Figure 1). The mixture of the starting material in the microwave vial seen in Figure 2a shows the heterogeneous suspension created by combining the starting materials in the 1 M HCl solvent. It is recommended to pre-mix the solution for a few seconds over a stir plate to ensure th...

Watch this Scientific Journal Video about Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines at JoVE.com

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

1-Aryl-1H-pyrazole-5-amines are prepared from aryl hydrazines combined with either 3-aminocrotononitrile or an &#945;-cyanoketone in a 1 M HCl solution using a microwave reactor. Most reactions are done in 10-15 minutes and pure product can be obtained via vacuum filtration with typical isolated yields of 70-90%.

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

A synthetic process for the preparation of a variety of 1-aryl-1H-pyrazole-5-amines was developed. The microwave-mediated nature of this method makes it ...

microwave-assisted-preparation-of-1-aryl-1h-pyrazole-5-amines

Research

Education

JoVE Core

JoVE Journal

Organic Chemistry

Chemistry

Unit 1

Aromatic Compounds

SCIENTISTS IN ACTION

6.6K Views.  California Polytechnic State University. 1-Aryl-1H-pyrazole-5-amines are prepared from aryl hydrazines combined with either 3-aminocrotononitrile or an α-cyanoketone in a 1 M HCl solution using a microwave reactor. Most reactions are done in 10-15 minutes and pure product can be obtained via vacuum filtration with typical isolated yields of 70-90%.

Video: Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to the preparation of new organic dyes. Although numerous strategies have been reported to access naphthalene scaffolds, many procedures still present limitations in terms of incorporating functionality, which in turn narrows the range of available substrates. The development of versatile methods for direct access to substituted naphthalenes is therefore highly desirable.
The Diels-Alder (DA) cycloaddition reaction is a powerful and attractive method for the formation of saturated and unsaturated ring systems from readily available starting materials. A new microwave-assisted intramolecular dehydrogenative DA reaction of styrenyl derivatives described herein generates a variety of functionalized cyclopenta[b]naphthalenes that could not be prepared using existing synthetic methods. When compared to conventional heating, microwave irradiation accelerates reaction rates, enhances yields, and limits the formation of undesired byproducts.
The utility of this protocol is further demonstrated by the conversion of a DA cycloadduct into a novel solvatochromic fluorescent dye via a Buchwald-Hartwig palladium-catalyzed cross-coupling reaction. Fluorescence spectroscopy, as an informative and sensitive analytical technique, plays a key role in research fields including environmental science, medicine, pharmacology, and cellular biology. Access to a variety of new organic fluorophores provided by the microwave-assisted dehydrogenative DA reaction allows for further advancement in these fields.

Microwave-assisted intramolecular dehydrogenative Diels-Alder (DA) reactions provide concise access to functionalized cyclopenta[b]naphthalene building blocks. The utility of this methodology is demonstrated by one-step conversion of the dehydrogenative DA cycloadducts into novel solvatochromic fluorescent dyes via Buchwald-Hartwig palladium-catalyzed cross-coupling reactions.

Functionalized naphthalenes have applications in a variety of research fields ranging from the synthesis of natural or biologically active molecules to ...

Facile Preparation of 4-Substituted Quinazoline Derivatives

Reported in this paper is a very simple method for direct preparation of 4-substituted quinazoline derivatives from a reaction between substituted 2-aminobenzophenones and thiourea in the presence of dimethyl sulfoxide (DMSO). This is a unique complementary reaction system in which thiourea undergoes thermal decomposition to form carbodiimide and hydrogen sulfide, where the former reacts with 2-aminobenzophenone to form 4-phenylquinazolin-2(1H)-imine intermediate, whilst hydrogen sulfide reacts with DMSO to give methanethiol or other sulfur-containing molecule which then functions as a complementary reducing agent to reduce 4-phenylquinazolin-2(1H)-imine intermediate into 4-phenyl-1,2-dihydroquinazolin-2-amine. Subsequently, the elimination of ammonia from 4-phenyl-1,2-dihydroquinazolin-2-amine affords substituted quinazoline derivative. This reaction usually gives quinazoline derivative as a single product arising from 2-aminobenzophenone as monitored by GC/MS analysis, along with small amount of sulfur-containing molecules such as dimethyl disulfide, dimethyl trisulfide, etc. The reaction usually completes in 4-6 hr at 160 &#186;C in small scale but may last over 24 hr when carried out in large scale. The reaction product can be easily purified by means of washing off DMSO with water followed by column chromatography or thin layer chromatography.

A protocol for facile preparation of 4-substituted quinazoline derivatives from 2-aminobenzophenones, thiourea and dimethyl sulfoxide is presented.

Reported in this paper is a very simple method for direct preparation of 4-substituted quinazoline derivatives from a reaction between substituted ...

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate glycosyl donor. Following azido-nitration of a glycal, the product 2-azido-1-nitrate ester can be hydrolyzed under microwave-assisted irradiation. This transformation is usually achieved using strongly nucleophilic reagents and extended reaction times. Microwave irradiation induces hydrolysis, in the absence of reagents, with short reaction times. Following denitration, the intermediate anomeric alcohol is converted, in the same pot, to the corresponding 2-azido-1-trichloroacetimidate.

A 2-azido-1-nitrate-ester can be converted to the corresponding 2-azido-1-trichloroacetimidate in a one-pot procedure. The goal of the manuscript is to demonstrate utility of the microwave reactor in carbohydrate synthesis.

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Preparation of N-(2-alkoxyvinyl)sulfonamides from N-tosyl-1,2,3-triazoles and Subsequent Conversion to Substituted Phthalans and Phenethylamines

Decomposition of N-tosyl-1,2,3-triazoles with rhodium(II) acetate dimer in the presence of alcohols forms synthetically versatile N-(2-alkoxyvinyl)sulfonamides, which react under a variety of conditions to afford useful N- and O-containing compounds. Acid-catalyzed addition of alcohols or thiols to N-(2-alkoxyvinyl)sulfonamide-containing phthalans provides access to ketals and thioketals, respectively. Selective reduction of the vinyl group in N-(2-alkoxyvinyl)sulfonamide-containing phthalans via hydrogenation yields the corresponding phthalan in good yield, whereas reduction with sodium bis(2-methoxyethoxy)aluminumhydride generates a ring-opened phenethylamine analogue. Because the N-(2-alkoxyvinyl)sulfonamide functional group is synthetically versatile, but often hydrolytically unstable, this protocol emphasizes key techniques in preparing, handling, and reacting these pivotal substrates in several useful transformations.

Preparation of N-2-alkoxyvinylsulfonamides from N-tosyl-1,2,3-triazoles and Subsequent Conversion to Substituted Phthalans and Phenethylamines

Representative experimental procedures for the synthesis of N-(2-alkoxyvinyl)sulfonamides and subsequent conversion to phthalan and phenethylamine derivatives are presented in detail.

Decomposition of N-tosyl-1,2,3-triazoles with rhodium(II) acetate dimer in the presence of alcohols forms synthetically versatile ...

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Bicyclic aziridinium ions were generated by the removal of an appropriate leaving group through internal nucleophilic attack by nitrogen atom in the aziridine ring. The utility of bicyclic aziridinium ions, specifically 1-azoniabicyclo[3.1.0]hexane and 1-azoniabicyclo[4.1.0]heptane tosylate highlighted in the aziridine ring openings by the nucleophile with the release of the ring strain to yield the corresponding ring-expanded azaheterocycles such as pyrrolidine, piperidine and azepane with diverse substituents on the ring in regio- and stereospecific manner. Herein, we report a simple and convenient method for the preparation of the stable 1-azabicyclo[4.1.0]heptane tosylate followed by selective ring opening via a nucleophilic attack either at the bridge or at the bridgehead carbon to yield piperidine and azepane rings, respectively. This synthetic strategy allowed us to prepare biologically active natural products containing piperidine and azepane motif including sedamine, allosedamine, fagomine and balanol in highly efficient manner.

Bicyclic aziridinium ions such as 1-azoniabicyclo[4.1.0]heptane tosylate were generated from 2-[4-tolenesulfonyloxybutyl]aziridine, which was utilized for the preparation of substituted piperidines and azepanes via regio- and stereospecific ring-expansion with various nucleophiles. This highly efficient protocol allowed us to prepare diverse azaheterocycles including natural products such as fagomine, febrifugine analogue and balanol.

Bicyclic aziridinium ions were generated by the removal of an appropriate leaving group through internal nucleophilic attack by nitrogen atom in the ...

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of &#945;-Imino &#947;-Lactones and Alkylidene Pyrazolones

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. Recently, we have developed an efficient organocatalytic strategy, which provides facile access to a variety of enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons. In this paper, we demonstrate a detailed protocol for the asymmetric synthesis of drug-like bispirocyclic compounds with two spirocyclic carbon centers via an organocatyltic 1,3-dipolar cycloaddition reaction. Spirocyclization synthons &#945;-imino &#947;-lactones and alkylidene pyrazolones are prepared first, which are then subjected to a cycloaddition reaction in the presence of a bifunctional squaramide organocatalyst to afford the desired bispirocycles in high yields and excellent stereoselectivities. Chiral high-performance liquid chromatography (HPLC) is carried out to determine the enantiomeric purity of the products, and the d.r. value is examined by proton nuclear magnetic resonance (1H NMR). The absolute configuration of the product is assigned according to an X-ray crystallographic analysis. This synthetic strategy allows scientists to prepare a diversity of bispirocyclic scaffolds in high yields and excellent diastereo- and enantioselectivities.

Enantiomerically enriched bispiro[&#947;-butyrolactone-pyrrolidin-4,4&#39;-pyrazolone] skeletons are asymmetrically synthesized through a simple organocatalytic 1,3-dipolar cycloaddition reaction.

Bispirocyclic scaffolds are one of the important structural subunits in many natural products that exhibit diverse and attractive biological activities. ...

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal catalysis, the literature on direct heteroarylation is scarce. The presence of heteroatoms such as nitrogen, sulfur and oxygen often make heteroarylation a challenging research field due to catalyst poisoning, product decomposition and the rest. This protocol details a highly efficient direct &#945;-C(sp3) heteroarylation of ketones under microwave irradiation. Key factors for successful heteroarylation include the use of XPhos Palladacycle Gen. 4 Catalyst, excess base to suppress side reactions and the high temperature and pressure achieved in a sealed reaction vial under microwave irradiation. The heteroarylation compounds prepared by this method were fully characterized by proton nuclear magnetic resonance spectroscopy (1H NMR), carbon nuclear magnetic resonance spectroscopy (13C NMR) and high-resolution mass spectrometry (HRMS). This methodology has several advantages over literature precedents including broad substrate scope, rapid reaction time, greener procedure and operational simplicity by eliminating the preparation of intermediates such as silyl enol ether. Possible applications for this protocol include, but are not limited to, diversity-oriented synthesis for the discovery of biologically active small molecules, domino synthesis for the preparation of natural products and ligand development for new transition metal catalytic systems.

Heteroaryl compounds are important molecules utilized in organic synthesis, medicinal and biological chemistry. A microwave-assisted heteroarylation using palladium catalysis provides a rapid and efficient method to attach heteroaryl moieties directly to ketone substrates.

Heteroarylation introduces heteroaryl fragments to organic molecules. Despite the numerous available reactions reported for arylation via transition metal ...

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Methine-bridged conjugated bicyclic aromatic compounds are common constituents of a range of biologically relevant molecules such as porphyrins, dipyrrinones, and pharmaceuticals. Additionally, restricted rotation of these systems often results in highly to moderately fluorescent systems as observed in 3H,5H-dipyrrolo[1,2-c:2',1'-f]pyrimidin-3-ones, xanthoglows, pyrroloindolizinedione analogs, BODIPY analogs, and the phenolic and imidazolinone ring systems of Green Fluorescent Protein (GFP). This manuscript describes an inexpensive and operationally simple method of performing a Claisen-Schmidt condensation to generate a series of fluorescent pH dependent pyrazole/imidazole/isoindolone dipyrrinone analogs. While the methodology illustrates the synthesis of dipyrrinone analogs, it can be translated to produce a wide range of conjugated bicyclic aromatic compounds. The Claisen-Schmidt condensation reaction utilized in this method is limited in scope to nucleophiles and electrophiles that are enolizable under basic conditions (nucleophile component) and non-enolizable aldehydes (electrophile component). Additionally, both the nucleophilic and electrophilic reactants must contain functional groups that will not inadvertently react with hydroxide. Despite these limitations, this methodology offers access to completely novel systems that can be employed as biological or molecular probes.

The Claisen-Schmidt condensation reaction is an important methodology for the generation of methine-bridged conjugated bicyclic aromatic compounds. Through utilizing a base-mediated variant of the aldol reaction, a range of fluorescent and/or biologically relevant molecules can be accessed through a generally inexpensive and operationally simple synthetic approach.

Methine-bridged conjugated bicyclic aromatic compounds are common constituents of a range of biologically relevant molecules such as porphyrins, ...

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

Nitrogen-containing heterocycle aziridines are synthetically very valuable for the preparation of azacyclic and acyclic molecules. However, it is very difficult and laborious to make aziridines in optically pure forms on a large scale to apply asymmetric synthesis of aza compounds. Fortunately, we successfully achieved both enantiomers (2R)- and (2S)-aziridine-2-carboxylates with the electron-donating &#945;-methylbenzyl group at the ring nitrogen as non-activated aziridines. These starting aziridines have two distinct functional groups-highly reactive three-membered ring and versatile carboxylate. They are applicable in ring-opening or ring-transformation with aziridine and in functional group transformation to others from carboxylate. Both of these enantiomers were utilized in the preparation of biologically important amino acyclic and/or aza-heterocyclic compounds in an asymmetric manner. Specifically, this report describes the first expedient asymmetric synthesis of both enantiomers of 5, 6-dihydrouracil-type marine natural products biemamide B and D as potential TGF-&#946; inhibitors. This synthesis consisted of regio- and the stereoselective ring-opening reaction of aziridine-2-carboxylate and subsequent formation of 4-aminoteterahydropyrimidine-2,4-dione. One more example in this protocol dealt a highly stereoselective Mukaiyama reaction of aziridine-2-carboxylate and silyl enol ether, following intramolecular aziridine ring-opening to provide easy and facile access to (-)-epiallo-isomuscarine.

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

In this study, we prepare both enantiomers of aziridine-2-carboxylate, which are used in the asymmetric synthesis of alkaloids, including biemamide B and D, and (-)-epiallo-isomuscarine.

Nitrogen-containing heterocycle aziridines are synthetically very valuable for the preparation of azacyclic and acyclic molecules. However, it is very ...

Preparation of 1&deg; Amines: Azide Synthesis

Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide synthesis method can be used.
Azide ions act as good nucleophiles and react with unhindered alkyl halides to form alkyl azides. Alkyl azides do not participate in further nucleophilic substitution reactions, thereby eliminating the chances of polyalkylated products. Alkyl azides are reduced by hydride-based reducing agents, like lithium aluminum hydride, or by catalytic hydrogenation to primary amines. The driving force for such reactions is the elimination of nitrogen gas.
Azide synthesis also works with other electrophiles like epoxides to produce amino alcohols through stereoselective ring-opening reactions. Alkyl azides have an explosive nature and must be carefully handled.

Preparation of 1&amp;deg; Amines: Azide Synthesis

Direct alkylation of ammonia produces polyalkylated amines, along with a quaternary ammonium salt. To exclusively prepare primary amines, the azide ...

Microwave-Assisted Preparation of 1-Aryl-1H-pyrazole-5-amines

Summary

Explore More Videos

Chapters in this video

Microwave-assisted Intramolecular Dehydrogenative Diels-Alder Reactions for the Synthesis of Functionalized Naphthalenes/Solvatochromic Dyes

Facile Preparation of 4-Substituted Quinazoline Derivatives

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

Preparation of N-(2-alkoxyvinyl)sulfonamides from N-tosyl-1,2,3-triazoles and Subsequent Conversion to Substituted Phthalans and Phenethylamines

Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles

Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones

A Microwave-Assisted Direct Heteroarylation of Ketones Using Transition Metal Catalysis

Synthesis of pH Dependent Pyrazole, Imidazole, and Isoindolone Dipyrrinone Fluorophores using a Claisen-Schmidt Condensation Approach

Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine

Preparation of 1° Amines: Azide Synthesis