Name: preparation of stable bicyclic aziridinium ions and their ring-opening for the synthesis of azaheterocycles
Uploaded: 2018-08-22T13:30:00
Description: Watch this Scientific Journal Video about Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles at JoVE.com

This work was supported by the National Research Foundation of Korea (NRF-2012M3A7B4049645 and HUFS Research Fund (2018).

1. Synthesis of (6R)-1-[(R)-1-Phenylethyl)-1-Azoniabicyclo[4.1.0]Heptane Tosylate (4)
<ol>
	<li>Synthesis of 4-(R)-[1-(R)-1-phenylethyl)aziridin-2-yl]butyl 4-methylbenzenesulfonate (2)
	<ol>
		<li>Add 100 mg of 4-[(R)-1-(R)-1-phenylethyl)aziridin-2-yl]butan-1-ol (1)12 (0.46 mmol, 1.0 equiv), 140 &#181;L of triethylamine (Et3N, 1.0 mmol, 2.2 equiv), and a magnetic stir-bar into an oven-dried 25 mL two-neck round-bott...

<ol>
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Commun. , 4363-4365 (2008).</li><li>D&#8217;hooghe, M., Van Speybroeck, V., Waroquier, M., De Kimpe, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regio-+and+stereospecific+ring+opening+of+1,1-dialkyl-2-(aryloxymethyl)aziridinium+salts+by+bromide.">Regio- and stereospecific ring opening of 1,1-dialkyl-2-(aryloxymethyl)aziridinium salts by bromide.</a> Chem. Commun. , 1554-1556 (2006).</li><li>Stankovic, S., D'hooghe, M., Catak, S., Eum, H., Waroquier, M., Van Speybroeck, V., De Kimpe, N., Ha, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Regioselectivity+in+the+ring+opening+of+non-activated+aziridines.">Regioselectivity in the ring opening of non-activated aziridines.</a> Chem. Soc. Rev. 41, 643-665 (2012).</li><li>Ji, M. K., Hertsen, D., Yoon, D. H., Eum, H., Goossens, H., Waroquier, M., Van Speybroeck, V., D'hooghe, M., De Kimpe, N., Ha, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nucleophile-Dependent+Regio-+and+Stereoselective+Ring+Opening+of+1-Azoniabicyclo[3.1.0]hexane+Tosylate.">Nucleophile-Dependent Regio- and Stereoselective Ring Opening of 1-Azoniabicyclo[3.1.0]hexane Tosylate.</a> Chem. Asian J. 9, 1060-1067 (2014).</li><li>Mtro, T. -. X., Duthion, B., Gomez Pardo, D., Cossy, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rearrangement+of+&#946;-amino+alcohols+viaaziridiniums:+a+review.">Rearrangement of &#946;-amino alcohols viaaziridiniums: a review.</a> Chem. Soc. Rev. 39, 89-102 (2010).</li><li>Dolfen, J., Yadav, N. N., De Kimpe, N., D'hooghe, M., Ha, H. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bicyclic+Aziridinium+Ions+in+Azaheterocyclic+Chemistry-Preparation+and+Synthetic+Application+of+1-Azoniabicyclo[n.1.0]alkanes.">Bicyclic Aziridinium Ions in Azaheterocyclic Chemistry-Preparation and Synthetic Application of 1-Azoniabicyclo[n.1.0]alkanes.</a> Adv. Synth. Catal. 358, 3485-3511 (2016).</li><li>Choi, J., Yadav, N. N., Ha, H. -. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+a+Stable+Bicyclic+Aziridinium+Ion+and+Its+Ring+Expansion+toward+Piperidines+and+Azepanes.">Preparation of a Stable Bicyclic Aziridinium Ion and Its Ring Expansion toward Piperidines and Azepanes.</a> Asian J. Org. Chem. 6, 1292-1307 (2017).</li><li>Yadav, N. N., Choi, J., Ha, H. -. J. <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+multiple+reactions:+asymmetric+synthesis+of+2,6-cis-disubstituted+piperidine+alkaloids+from+chiral+aziridine.">One-pot multiple reactions: asymmetric synthesis of 2,6-cis-disubstituted piperidine alkaloids from chiral aziridine.</a> Org. Biomol. Chem. 14, 6426-6434 (2016).</li><li>Angoli, M., Barilli, A., Lesma, G., Passarella, D., Riva, S., Silvani, A., Danieli, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remote+Stereocenter+Discrimination+in+the+Enzymatic+Resolution+of+Piperidine-2-ethanol.+Short+Enantioselective+Synthesis+of+Sedamine+and+Allosedamine.">Remote Stereocenter Discrimination in the Enzymatic Resolution of Piperidine-2-ethanol. Short Enantioselective Synthesis of Sedamine and Allosedamine.</a> J. Org. Chem. 68, 9525-9527 (2003).</li><li>Shaikh, T. M., Sudalai, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enantioselective+Synthesis+of+(+)-&#945;-Conhydrine+and+(-)-Sedamine+by+L-Proline-Catalysed+&#945;-Aminooxylation.">Enantioselective Synthesis of (+)-&#945;-Conhydrine and (-)-Sedamine by L-Proline-Catalysed &#945;-Aminooxylation.</a> Eur. J. Org. Chem. , 3437-3444 (2010).</li><li>Miyabe, H., Torieda, M., Inoue, K., Tajiri, K., Kiguchi, T., Naito, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Total+Synthesis+of+(&#8722;)-Balanol.">Total Synthesis of (&#8722;)-Balanol.</a> J. Org. Chem. 63, 4397-4407 (1998).</li><li>Castillo, J. A., Calveras, J., Casas, J., Mitjans, M., Vinardell, M. P., Parella, T., Inoue, T., Sprenger, G. 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Piperidine and azepane are two most abundant azaheterocycles in many life-saving drugs and antibiotics including various biologically active natural products16. In order to access both enantiopure piperidine (5) and azepane (6) with diverse substituents, we develped an efficient synthetic method through the formation of 1-azoniabicyclo[4.1.0]heptane tosylate from entiopure 2-(4-hydroxybutyl)aziridne followed by regiospecific nucleophilic attack either at the bridg...

Among three membered cyclic compounds, aziridine has similar ring strain energy as cyclopropane and oxirane to afford various nitrogen-containing cyclic and acyclic compounds via ring opening1,2,3. However, the characteristics and reactivity of aziridine depend on the substituent of ring nitrogen. Aziridine with an electron-withdrawing group at the ring nitrogen4, is called &#34;activated aziridine&#34;, which is activated to react with the incoming nucleophile without any additional activating reagent. On the other hand, &#34;non-activated aziridine&#34; with electron-donating substituent at nitrogen is quite stable and inert to the nucleophiles, unless it is activated as an aziridinium ion as Ia (Figure 1a)5,6,7. The ring opening of a non-activated aziridine depends on various factors such as the substituents at C2 and C3 carbon of aziridine, the electrophile to activate the aziridine ring and the incoming nucleophile. The isolation and characterization of an aziridinium ion is not possible due to its high reactivity towards ring-opening reaction by nucleophiles, but its formation and characteristics were observed spectroscopically with a non-nucleophilic counter anion5,8,9,10. The regio- and stereoselective ring-opening reaction of aziridinium ion by a suitable nucleophile yields nitrogen-containing acyclic valuable molecules (Pi and Pii)5,6,7,8,9,10.
Similarly, a bicyclic aziridinium ion (Ib) is possibly generated via the removal of the leaving group by the nucleophilic attack of ring nitrogen of aziridine in intramolecular fashion (Figure 1b). Then, this intermediate undergoes ring-expansion with the incoming nucleophile via the release of ring strain. The formation and stability of bicyclic aziridinium ion are dependent on many factors such as the substituents, the size of the ring, and solvent medium9. The regio- and stereoselectivity of the aziridine ring-expansion is a pivotal aspect of its synthetic utility, which depends on the nature of the substituents in the starting substrate and the characteristics of applied nucleophile.
In our early study, we succeeded to prepare 1-azoniabicyclo [3.1.0]hexane tosylate Ib (n = 1) whose subsequent ring-expansion resulted in the formation of a pyrrolidine and a piperidine (Piii and Piv, n = 1, Figure 1)8. As a part of our continuing study on the bicyclic aziridinium ion chemistry, we describes herein the formation of 1-azoniabicyclo [4.1.0]heptane tosylate Ib (n = 2) as a representative example. This was prepared from 2-(4-toluensulfonyloxybutyl)aziridine and its ring-expansion was trigged by a nucleophile to afford valuable piperidine and azepane (Pi and Pii, n = 2, Figure 1) with diverse substituents around the ring11. The ring-expansion of enantiopure aziridine 4-[(R)-1-(R)-1-phenylethyl)aziridin-2-yl]butan-1-ol (1) resulted in the asymmetric synthesis of substituted azaheterocycles which are applicable to build biologically active molecules with piperidine and azepane skeleton. This synthetic protocol has been applied for various compounds ranging from simple 2-cyanomethylpiperidine 5f, 2-acetyloxymethylpiperidine 5h and 3-hydroxyazepane 6j to more complex molecules including natural products such as fagomine (9), febrifugine analogue (12) and balanol (15) in optically pure forms11.

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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Thin Layer Chromatography (TLC)</td>
			<td style="width:260px;">Merck</td>
			<td style="width:207px;">100390</td>
			<td style="width:183px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">UV light</td>
			<td style="width:260px;">Sigma-Aldrich</td>
			<td>Z169625-1EA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Bruker AVANCE III HD (400 MHz) spectrometer</td>
			<td style="width:260px;">Bruker</td>
			<td style="width:207px;">NA</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">JASCO P-2000</td>
			<td style="width:260px;">JASCO</td>
			<td style="width:207px;">P-2000</td>
			<td>For optical rotation</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">High resolution mass spectra/ MALDI-TOF/TOF Mass Spectrometry</td>
			<td style="width:260px;">AB SCIEX</td>
			<td style="width:207px;">4800 Plus&#160;</td>
			<td>High resolution mass spectra</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">(2R)-1-[(1R)-1-Phenylethyl]-2-aziridinecarboxylic acid (&#8211;)-menthol ester, 98%</td>
			<td style="width:260px;">Sigma-Aldrich</td>
			<td style="width:207px;">57,054-0</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">(2S)-1-[(1R)-1-Phenylethyl]-2-aziridinecarboxylic acid (&#8211;)-menthol ester</td>
			<td style="width:260px;">Sigma-Aldrich</td>
			<td style="width:207px;">57,051-6</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Triethylethylamine</td>
			<td style="width:260px;">DAEJUNG</td>
			<td style="width:207px;">8556-4400-1L</td>
			<td>CAS No: 121-44-8</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Dichloromethane</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">M0822-18L</td>
			<td>CAS No: 75-09-2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">p-Toluenesulfonic anhydride</td>
			<td style="width:260px;">Sigma-Aldrich</td>
			<td style="width:207px;">259764-25G</td>
			<td>CAS No: 4124-41-8</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">n-Hexane</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">H0114-18L</td>
			<td>CAS No: 110-54-3</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Ethyl acetate</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">E0191-18L</td>
			<td>CAS No: 141-78-6</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium sulfate</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">S1011-1kg</td>
			<td>CAS No: 7757-82-6</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Acetonitrile-d3</td>
			<td style="width:260px;">Cambridge Isotope Laboratories, Inc</td>
			<td style="width:207px;">15G-744-25g</td>
			<td>CAS No: 2206-26-0</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Acetonitrile</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">A0127-18L</td>
			<td>CAS No: 75-05-8</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">1,4-Dioxane</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">D0654-1kg</td>
			<td>CAS No: 123-91-1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium hydroxide</td>
			<td style="width:260px;">DUKSAN</td>
			<td style="width:207px;">A31226-1kg</td>
			<td>CAS No: 1310-73-2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium acetate</td>
			<td style="width:260px;">Alfa Aesar</td>
			<td style="width:207px;">11554-250g</td>
			<td>CAS No: 127-09-3</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Lithium aluminum hydride</td>
			<td style="width:260px;">TCI</td>
			<td style="width:207px;">L0203-100g</td>
			<td>CAS No: 16853-85-3</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Tetrahydrofuran</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">T0148-18L</td>
			<td>CAS No: 109-99-9</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium azide</td>
			<td style="width:260px;">D.S.P</td>
			<td style="width:207px;">703301-500g</td>
			<td>CAS No: 26628-22-8</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Cesium fluoride</td>
			<td style="width:260px;">aldrich</td>
			<td style="width:207px;">18951-0250-25g</td>
			<td>CAS No: 13400-13-0</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Tetrabutylammonium bromide</td>
			<td style="width:260px;">aldrich</td>
			<td style="width:207px;">426288-25g</td>
			<td>CAS No: 1643-19-2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium iodide</td>
			<td style="width:260px;">aldrich</td>
			<td style="width:207px;">383112-100g</td>
			<td>CAS No: 7681-82-5</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium cyanide</td>
			<td style="width:260px;">Acros Organics</td>
			<td style="width:207px;">424301000-100g</td>
			<td>CAS No: 143-33-9</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium thiocyanate</td>
			<td style="width:260px;">aldrich</td>
			<td style="width:207px;">467871-250g</td>
			<td>CAS No: 540-72-7</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium methoxide</td>
			<td style="width:260px;">aldrich</td>
			<td style="width:207px;">156256-1L</td>
			<td>CAS No: 124-41-4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Benzylamine</td>
			<td style="width:260px;">Alfa Aesar</td>
			<td style="width:207px;">A10997-1000g</td>
			<td>CAS No: 100-46-9</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Phenol</td>
			<td style="width:260px;">TCI</td>
			<td style="width:207px;">P1610-500g</td>
			<td>CAS No: 108-95-2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Sodium benzoate</td>
			<td style="width:260px;">Alfa Aesar</td>
			<td style="width:207px;">A15946-250g</td>
			<td>CAS No: 532-32-1</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:564px;">Chloroform-d</td>
			<td style="width:260px;">Cambridge Isotope Laboratories, Inc</td>
			<td style="width:207px;">DLM-7TB-100S/16H-239, 100g</td>
			<td>CAS No: 865-49-6</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Dimethyl sulfoxide-d6</td>
			<td style="width:260px;">Cambridge Isotope Laboratories, Inc</td>
			<td style="width:207px;">DLM-10-25, 25g</td>
			<td>CAS No: 2206-27-1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Methanol</td>
			<td style="width:260px;">SAMCHUN</td>
			<td style="width:207px;">M0585-18L</td>
			<td>CAS No: 67-56-1</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Ninhydrin</td>
			<td style="width:260px;">Alfa Aesar</td>
			<td style="width:207px;">A10409-250g</td>
			<td>CAS No: 485-47-2</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">Phosphomolybdic acid hydrate</td>
			<td style="width:260px;">TCI</td>
			<td style="width:207px;">P1910-100g</td>
			<td>CAS No: 51429-74-4</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:564px;">p-Anisaldehyde</td>
			<td style="width:260px;">aldrich</td>
			<td style="width:207px;">A88107-5g</td>
			<td>CAS No: 123-11-5</td>
		</tr>
	</tbody>
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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.

The reaction of 4-[(R)-1-(R)-1-phenylethyl)aziridin-2-yl]butan-1-ol (1)12 with p-toluenesulfonic anhydride and triethylamine in CH2Cl2 at room temperature for 1.0 h yielded the corresponding 2-(4-tosyloxybutyl)aziridine 2 in 96% yield11. 1H NMR (400 MHz) spectrum of compound 2 in CD3CN at different time intervals shows th...

Watch this Scientific Journal Video about Preparation of Stable Bicyclic Aziridinium Ions and Their Ring-Opening for the Synthesis of Azaheterocycles at JoVE.com

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

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 ...

This method can help to answer key questions in the field of bicyclic aziridinium ion chemistry for the synthesis of various various azaheterocycles including bipyridine and azepine ring systems. The main advantage of this technique is that the synthesis of kai-dal bipyridines and azepine core present in various natural products is achieved in a straight-forward manner. First, add 100 milligrams of the alcohol, 140 microliters of triethylamine, and a magnetic stir bar into an oven dried 25 milliliter two-neck round bottom flask under nitrogen atmosphere.Using an airtight syringe, add 5 milliliters of anhydrous dichloromethane to the reaction flask. Cool the reaction mixture to 0 degrees Celsius using an ice water bath and stir the mixture for 5 minutes. Next, add 164 milligrams of p-toluenesulfonic anhydride to the reaction mixture and stir for another 45 minutes.After stirring for 45 minutes, warm the reaction mixture to room temperature and stir for 30 minutes. Monitor the reaction progress by thin layer chromatography using hexanes and ethyl acetate as the eluant. After the complete consumption of the starting alcohol, quench the reaction mixture with 5 milliliters of water.Then extract the heterogeneous mixture three times with 15 milliliters of dichloromethane. Dry the combined organic layer over anhydrous sodium sulfate for 10 minutes. After filtration, concentrate the filtrate in vacuo using a rotary evaporator.Purify the crude product by flash-column chromatography using a gradient of hexanes and ethyl acetate to afford the tosylate in 96%yield as a viscous liquid. Now, transfer 5 milligrams of the tosylate in an NMR tube and add 300 microliters of deuterated acetonitrile. Set aside this solution at room temperature for 24 hours to attain complete conversion to the azoniabicyclo.Monitor the conversion by NMR at different time points. Add 160 milligrams of the previously prepared tosylate and a magnetic stir bar into an oven-dried 25 milliliter round-bottom flask. Using an airtight syringe, add 4 milliliters of anhydrous acetonitrile to the reaction flask.Add three equivalents of a suitable nucleophile to the reaction mixture and stir for 8 to 15 hours. Once the reaction is complete, quench the mixture with 5 milliliters of water. Then extract three times with 15 milliliters of dichloromethane.Dry the combined organic layer over anhydrous sodium sulfate. After filtration, concentrate the filtrate in vacuo using a rotary evaporator. Purify the crude product by column chromatography using a gradient of hexanes and ethyl acetate to afford the pure ring expanded products.Transfer 100 milligrams of the aziridinyl tosylate and a magnetic stir bar into an oven dried 25 milliliter round-bottom flask fitted with a reflux condenser. Using a syringe, add 4 milliliters of 1, 4-dioxane to the reaction flask. Add 0.4 milliliters of 2 molar sodium hydroxide solution to the reaction mixture and heat to reflux for 2 hours.Once the reaction is complete, quench the mixture with 4 milliliters of water. Then extract the reaction mixture four times with 15 milliliters of dichloromethane. Dry the combined organic layer over anhydrous sodium sulfate.After filtration, concentrate the filtrate in vacuo using a rotary evaporator. Purify the crude product by column chromatography using a gradient of hexanes and ethyl acetate to afford the pure hydroxy-azepane in a 97%yield. Transfer 220 milligrams of the aziridinyl alcohol, 180 microliters of triethylamine, and a magnetic stir bar into an oven-dried 25 milliliter two-neck round-bottom flask under nitrogen atmosphere.Using an airtight syringe, add 4 milliliters of anhydrous dichloromethane to the reaction flask. Cool the reaction mixture to 0 degrees Celsius, and stir for 5 minutes. Following this, add 200 milligrams of p-toluenesulfonic anhydride to the reaction mixture, and stir for another 45 minutes.Then warm the reaction mixture to room temperature, and stir for 30 minutes. Monitor the reaction progress by thin layer chromatography using hexanes and ethyl acetate as the eluant. After the complete consumption of the alcohol, quench the reaction mixture with 5 milliliters of water.Then extract three times with 15 milliliters of dichloromethane. Dry the combined organic layer over anhydrous sodium sulfate. After filtration, concentrate the filtrate in vacuo using a rotary evaporator.Now, transfer the crude tosylate and a magnetic stir bar into an oven-dried 25 milliliter round-bottom flask. Using an airtight syringe, add 4 milliliters of anhydrous acetonitrile to the reaction flask. Next, add 125 milligrams of sodium acetate to the reaction mixture and stir for 12 hours.Once the reaction is complete, quench the mixture with 5 milliliters of water. Then extract three times with 15 milliliters of dichloromethane. Dry the combined organic layer over anhydrous sodium sulfate.After filtration, concentrate the filtrate in vacuo using a rotary evaporator. Finally, purify the crude product by column chromatography using a gradient of hexanes and ethyl acetate to afford the pure substituted properidine in 83%yield. The proton NMR spectrum of tosylate-2 at different time intervals shows the conversion to azoniabicyclo.A quartet at 4.07 PPM in the NMR spectrum of ring expanded product 5a corresponds to the CH proton of phenylethyl group. A similar quartet at 3.81 PPM was observed for ring expanded product 6a. The aziridine ring expansion of cyanide, thiocyanide, and acetate nucleophiles afforded properidine rings, while azide, hydroxide, and amine nucleophiles yielded azepane rings.Synthesis of natural azasugar d-fagomine and its three epimer was achieved by ring expansion of aziridinyl-alcohol-7, followed by removal of the protecting groups to afford the product in 94%yield. Benzyl protected alcohol-10 was treated with p-toluenesulfonic anhydride and triethylamine followed by nucleophilic ring opening resulting in the ring-expanded cyanomethyl-properidine-11 in 90%yield as a single isomer. The ring expansion of alcohol-13 followed by reaction with sodium azide yielded hydroxy-azapane-14 which was used for the azepane core of Balanol by one-pot benzyl deprotection and azide reduction under catalytic hydrogenation.Once mastered, this technique for aziridine ring expansion can be done in six to eight hours if it is performed properly. While attempting this procedure, it is important to remember to use para-toluenesulfonic anhydride, because it is more sensitive to moisture. Following this procedure, other methods like use of para-toluenesulfonic chloride instead of para-toluenesulfonic anhydride can be used in order to explore the eco-friendly nature of the pro-gen protocol.After its development, this technique paved the way for the researchers in the field of synthetic organic chemistry to explore the environment of aziridinium ion in azaheterocycles and natural product synthesis. After watching this video, you should have a good understanding of how to use bicyclic aziridinium ion chemistry for the synthesis of biologically-relevant molecules having an azaheterocycles including a variety of natural products. Don't forget that working with toxic reagents such as sodium cyanide used in the synthesis as a nucleophile can be extremely hazardous, and extreme safety precautions should always be taken while performing this procedure.

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Nucleophilic Substitution and Elimination Reactions of Alkyl Halides

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Amide Coupling Reaction for the Synthesis of Bispyridine-based Ligands and Their Complexation to Platinum as Dinuclear Anticancer Agents

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. Isonicotinic acid, or its derivatives, are coupled to variable length diaminoalkane chains under an inert atmosphere in anhydrous DMF or DMSO with the use of a weak base, triethylamine, and a coupling agent, 1-propylphosphonic anhydride. The products precipitate from solution upon formation or can be precipitated by the addition of water. If desired, the ligands can be further purified by recrystallization from hot water. Dinuclear platinum complex synthesis using the bispyridine ligands is done in hot water using transplatin. The most informative of the chemical characterization techniques to determine the structure and gross purity of both the bispyridine ligands and the final platinum complexes is 1H NMR with particular analysis of the aromatic region of the spectra (7-9 ppm). The platinum complexes have potential application as anticancer agents and the synthesis method can be modified to produce trinuclear and other multinuclear complexes with different hydrogen bonding functionality in the bridging ligand.

This protocol describes the use of amide coupling reactions of isonicotinic acid and diaminoalkanes to form bridging ligands suitable for use in the synthesis of multinuclear platinum complexes, which combine aspects of the anticancer drugs BBR3464 and picoplatin.

Amide coupling reactions can be used to synthesize bispyridine-based ligands for use as bridging linkers in multinuclear platinum anticancer drugs. ...

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma sintering techniques. Polycrystalline ceramics possessing a unique morphology can be achieved by optimizing the process parameters, particularly spark plasma sintering heating rate. The phase and morphology of the synthesized ceramics were investigated in detail using X-ray diffraction, scanning electron microcopy and energy-dispersive X-ray spectroscopy. It was observed that the grains of these bulk Pr-doped SrTiO3 ceramics were enhanced with Pr-rich grain boundaries. Electronic and thermal transport properties were also investigated as a function of temperature and doping concentration. Such a microstructure was found to give rise to improved thermoelectric properties. Specifically, it resulted in a significant improvement in carrier mobility and the thermoelectric power factor. Simultaneously, it also led to a marked reduction in the thermal conductivity. As a result, a significant improvement (> 30%) in the thermoelectric figure of merit was achieved for the whole temperature range over all previously reported maximum values for SrTiO3-based ceramics. This synthesis demonstrates the steps for the preparation of bulk polycrystalline ceramics of non-uniformly Pr-doped SrTiO3.

Synthesis of Non-uniformly Pr-doped SrTiO3 Ceramics and Their Thermoelectric Properties

A protocol for the synthesis and processing of polycrystalline SrTiO3 ceramics doped non-uniformly with Pr is presented along with the investigation of their thermoelectric properties.

We demonstrate a novel synthesis strategy for the preparation of Pr-doped SrTiO3 ceramics via a combination of solid state reaction and spark plasma ...

A Simple Method for the Size Controlled Synthesis of Stable Oligomeric Clusters of Gold Nanoparticles under Ambient Conditions

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like oligomeric clusters of these yellow nanoparticles of narrow size distribution are synthesized under ambient conditions via two methods. The delay-time method controls the number of subunits in the oligoclusters by varying the time between the addition of HAuCl4 to alkaline solution and the subsequent addition of reducing agent, NaSCN. The yellow oligoclusters produced range in size from ~3 to ~25 nm. This size range can be further extended by an add-on method utilizing hydroxylated gold chloride (Na+[Au(OH4-x)Clx]-) to auto-catalytically increase the number of subunits in the as-synthesized oligocluster nanoparticles, providing a total range of 3 nm to 70 nm. The crude oligocluster preparations display narrow size distributions and do not require further fractionation for most purposes. The oligoclusters formed can be concentrated &#62;300 fold without aggregation and the crude reaction mixtures remain stable for weeks without further processing. Because these oligomeric clusters can be concentrated before derivatization they allow expensive derivatizing agents to be used economically. In addition, we present two models by which predictions of particle size can be made with great accuracy.

We describe a simple method for producing highly stable oligomeric clusters of gold nanoparticles via the reduction of chloroauric acid (HAuCl4) with sodium thiocyanate (NaSCN). The oligoclusters have a narrow size distribution and can be produced with a wide range of sizes and surface coats.

Reducing dilute aqueous HAuCl4 with sodium thiocyanate (NaSCN) under alkaline conditions produces 2 to 3 nm diameter nanoparticles. Stable grape-like ...

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the development of antibody drug conjugates (ADCs) and nanomedicine, fluorescent microscopy and systems chemistry. For many of these applications, specificity of the bioconjugation method used is of prime concern. The Michael addition of maleimides with cysteine(s) on the target proteins is highly selective and proceeds rapidly under mild conditions, making it one of the most popular methods for protein bioconjugation.
We demonstrate here the modification of the only surface-accessible cysteine residue on yeast cytochrome c with a ruthenium(II) bisterpyridine maleimide. The protein bioconjugation is verified by gel electrophoresis and purified by aqueous-based fast protein liquid chromatography in 27% yield of isolated protein material. Structural characterization with MALDI-TOF MS and UV-Vis is then used to verify that the bioconjugation is successful. The protocol shown here is easily applicable to other cysteine - maleimide coupling of proteins to other proteins, dyes, drugs or polymers.

Synthesis of Protein Bioconjugates via Cysteine-maleimide Chemistry

This protocol details the important steps required for the bioconjugation of a cysteine containing protein to a maleimide, including reagent purification, reaction conditions, bioconjugate purification and bioconjugate characterization.

The chemical linking or bioconjugation of proteins to fluorescent dyes, drugs, polymers and other proteins has a broad range of applications, such as the ...

Synthesis of Cyclic Polymers and Characterization of Their Diffusive Motion in the Melt State at the Single Molecule Level

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single molecule level. An electrostatic self-assembly and covalent fixation (ESA-CF) process is used for the synthesis of the cyclic poly(tetrahydrofuran) (poly(THF)). The diffusive motion of individual cyclic polymer chains in a melt state is visualized using single molecule fluorescence imaging by incorporating a fluorophore unit in the cyclic chains. The diffusive motion of the chains is quantitatively characterized by means of a combination of mean-squared displacement (MSD) analysis and a cumulative distribution function (CDF) analysis. The cyclic polymer exhibits multiple-mode diffusion which is distinct from its linear counterpart. The results demonstrate that the diffusional heterogeneity of polymers that is often hidden behind ensemble averaging can be revealed by the efficient synthesis of the cyclic polymers using the ESA-CF process and the quantitative analysis of the diffusive motion at the single molecule level using the MSD and CDF analyses.

A protocol for the synthesis and characterization of diffusive motion of cyclic polymers at the single molecule level is presented.

We demonstrate a method for the synthesis of cyclic polymers and a protocol for characterizing their diffusive motion in a melt state at the single ...

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of Phosphorus(I)

We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable low-valent-phosphorus-containing compound acts as a useful P+ transfer agent. Unlike traditional methods employed to access low-coordinate phosphorus species which usually require pyrophoric phosphorus-containing precursors (white phosphorus, Tris(trimethylsilyl)phosphine, etc.), or harsh reducing agents (alkali metals, potassium graphite, etc.), the current approach does not involve pyrophoric or explosive reagents and can be done on large scales (&#62;20 g) in excellent yields by undergraduates with basic air-free synthetic training. The bromide counter ion is readily exchanged with other anions such as tetraphenyl borate (described herein) using typical salt metathesis reagents to obtain materials with desired properties and reactivities. The versatility of this P+ transfer approach is exemplified by the reactions of these triphosphenium precursors with an N-heterocyclic carbene and an anionic bisphosphine, each of which readily displace the neutral bisphosphine to give an NHC-stabilized phosphorus(I) cation and a phosphorus(I) containing zwitterion, respectively.

Preparation and Reactivity of a Triphosphenium Bromide Salt: A Convenient and Stable Source of PhosphorusI

The synthesis of a triphosphenium bromide salt is described and its use as a P+ transfer agent is outlined by reactions with an N-heterocyclic carbene and an anionic bisphosphine, yielding an NHC-stabilized P(I) cation and a P(I) containing zwitterion, respectively.

We present herein the optimized synthesis of a triphosphenium bromide salt. Apart from being a versatile metathesis reagent, this unusually stable ...

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, allowing for the synthesis of isotactic poly(&#945;-hydroxy acids) with expected molecular weights (&#62;140 kDa) and narrow molecular weight distributions (Mw/Mn &#60; 1.1). This ring-opening polymerization is mediated by Ni and Zn complexes in the presence of an alcohol initiator and a photoredox Ir catalyst, irradiated by a blue LED (400 - 500 nm). The polymerization is performed at a low temperature (-15 &#176;C) to avoid undesired side reactions. The complete monomer consumption can be achieved within 4 - 8 hours, providing a polymer close to the expected molecular weight with narrow molecular weight distribution. The resulted number-average molecular weight shows a linear correlation with the degree of polymerization up to 1000. The homodecoupling 1H NMR study confirms that the obtained polymer is isotactic without epimerization. This polymerization reported herein offers a strategy for achieving rapid, controlled O-carboxyanhydrides polymerization to prepare stereoregular poly(&#945;-hydroxy acids) and its copolymers bearing various functional side-chain groups.

Controlled Photoredox Ring-Opening Polymerization of O-Carboxyanhydrides Mediated by Ni/Zn Complexes

A protocol for the controlled photoredox ring-opening polymerization of O-carboxyanhydrides mediated by Ni/Zn complexes is presented.

Here, we describe an effective protocol that combines photoredox Ni/Ir catalysis with the use of a Zn-alkoxide for efficient ring-opening polymerization, ...

Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes and determine the corresponding photochemical mechanism. Then, we describe a protocol to perform ring-opening metathesis polymerization (ROMP) in solution and in miniemulsion using this NHC-photogenerating system. To photogenerate IMes, a system comprising 2-isopropylthioxanthone (ITX) as the sensitizer and 1,3-dimesitylimidazolium tetraphenylborate (IMesH+BPh4-) as the protected form of NHC is employed. IMesH+BPh4- can be obtained in a single step by anion exchange between 1,3-dimesitylimidazolium chloride and sodium tetraphenylborate. A real-time steady-state photolysis setup is described, which hints that the photochemical reaction proceeds in two consecutive steps: 1) ITX triplet is photo-reduced by the borate anion and 2) subsequent proton transfer takes place from the imidazolium cation to produce the expected NHC IMes. Two separate characterization protocols are implemented. Firstly, CS2 is added to the reaction media to evidence the photogeneration of NHC through formation of the IMes-CS2 adduct. Secondly, the amount of NHC released in situ is quantified using acid-base titration. The use of this NHC photo-generating system for the ROMP of norbornene is also discussed. In solution, a photopolymerization experiment is conducted by mixing ITX, IMesH+BPh4-, [RuCl2(p-cymene)]2 and norbornene in CH2Cl2, then irradiating the solution in a UV reactor. In a dispersed medium, a monomer miniemulsion is first formed then irradiated inside an annular reactor to produce a stable poly(norbornene) latex.

We describe a protocol to photogenerate N-heterocyclic carbenes (NHCs) by UV irradiation of a 2-isopropylthioxanthone/imidazolium tetraphenylborate salt system. Methods to characterize the photoreleased NHC and elucidate the photochemical mechanism are proposed. The protocols for ring-opening metathesis photopolymerization in solution and miniemulsion illustrate the potential of this 2-component NHC photogenerating system.

We report a method to generate the N-heterocyclic carbene (NHC) 1,3-dimesitylimidazol-2-ylidene (IMes) under UV-irradiation at 365 nm to characterize IMes ...

Synthesis of In37P20(O2CR)51 Clusters and Their Conversion to InP Quantum Dots

This text presents a method for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots. The In37P20(O2CR)51 clusters have been observed as intermediates in the synthesis of InP quantum dots from molecular precursors (In(O2CR)3, HO2CR, and P(SiMe3)3) and may be isolated as a pure reagent for subsequent study and use as a single-source precursor. These clusters readily convert to crystalline and relatively monodisperse samples of quasi-spherical InP quantum dots when subjected to thermolysis conditions in the absence of additional precursors above 200 &#176;C. The optical properties, morphology, and structure of both the clusters and quantum dots are confirmed using UV-Vis spectroscopy, photoluminescence spectroscopy, transmission electron microscopy, and powder X-ray diffraction. The molecular symmetry of the clusters is additionally confirmed by solution-phase 31P NMR spectroscopy. This protocol demonstrates the preparation and isolation of atomically-precise InP clusters, and their reliable and scalable conversion to InP QDs.

Synthesis of In37P20O2CR51 Clusters and Their Conversion to InP Quantum Dots

A protocol for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots is presented.

This text presents a method for the synthesis of In37P20(O2C14H27)51 clusters and their conversion to indium phosphide quantum dots. The In37P20(O2CR)51 ...

Synthesis of Information-bearing Peptoids and their Sequence-directed Dynamic Covalent Self-assembly

This protocol presents the use of Lewis acidic multi-role reagents to circumvent kinetic trapping observed during the self-assembly of information-encoded oligomeric strands mediated by paired dynamic covalent interactions in a manner mimicking the thermal cycling commonly employed for the self-assembly of complementary nucleic acid sequences. Primary amine monomers bearing aldehyde and amine pendant moieties are functionalized with orthogonal protecting groups for use as dynamic covalent reactant pairs. Using a modified automated peptide synthesizer, the primary amine monomers are encoded into oligo(peptoid) strands through solid-phase submonomer synthesis. Upon purification by high-performance liquid chromatography (HPLC) and characterization by electrospray ionization mass spectrometry (ESI-MS), sequence-specific oligomers are subjected to high-loading of a Lewis acidic rare-earth metal triflate which both deprotects the aldehyde moieties and affects the reactant pair equilibrium such that strands completely dissociate. Subsequently, a fraction of the Lewis acid is extracted, enabling annealing of complementary sequence-specific strands to form information-encoded molecular ladders characterized by matrix assisted laser desorption/ionization mass spectrometry (MALDI-MS). The simple procedure outlined in this report circumvents kinetic traps commonly experienced in the field of dynamic covalent assembly and serves as a platform for the future design of robust, complex architectures.

A protocol is presented for the synthesis of information-encoded peptoid oligomers and for the sequence-directed self-assembly of these peptoids into molecular ladders using amines and aldehydes as dynamic covalent reactant pairs and Lewis acidic rare-earth metal triflates as multi-role reagents.

This protocol presents the use of Lewis acidic multi-role reagents to circumvent kinetic trapping observed during the self-assembly of information-encoded ...