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Concerted vs. Non-Concerted 1,3-Dipolar Cycloadditions of Azomethine Ylides to Electron-Deficient Dialkyl 2,3-Dicyanobut-2-enedioates


Khlebnikov, Alexander F; Konev, Alexander S; Virtsev, Alexander A; Yufit, Dmitri S; Mloston, Grzegorz; Heimgartner, Heinz (2014). Concerted vs. Non-Concerted 1,3-Dipolar Cycloadditions of Azomethine Ylides to Electron-Deficient Dialkyl 2,3-Dicyanobut-2-enedioates. Helvetica Chimica Acta, 97:453-470.

Abstract

The quantum-chemical calculations of the thermal ring opening of 1-methyl-2,3-diphenyl- and 1,2,3-triphenylaziridine with formation of the corresponding azomethine ylides of S-, U-, and W-type as well as their cycloaddition to dimethyl acetylenedicarboxylate (DMAD) and dimethyl 2,3-dicyanobut-2- enedioate, were performed at the DFT B3LYP/6-31G(d) level of theory with the PCM solvation model. The calculations are in complete accordance with experimental results and explain the switch from the concerted to the non-concerted pathway depending on substituents in the dipolarophile and the ylide. It was found that strong electron-withdrawing substituents in dipolarophiles, such as in dialkyl dicyanobutenedioates, significantly reduce the barrier for the formation of zwitterionic intermediates in the reaction of azomethine ylides with such dipoles. This can render the stepwise cycloaddition competitive with the concerted one. However, the concertedness of the cycloaddition even to dipolarophiles with several electron-withdrawing substituents is governed by a fine balance of electronic and steric effects in both ylide and dipolarophile counterparts. The hypothesis that introduction of substituents in the azo- methine ylide that destabilize the positive charge in a corresponding zwitterion will favor the concerted cycloaddition even with dialkyl dicyanobutenedioates was tested theoretically and experimentally.

Abstract

The quantum-chemical calculations of the thermal ring opening of 1-methyl-2,3-diphenyl- and 1,2,3-triphenylaziridine with formation of the corresponding azomethine ylides of S-, U-, and W-type as well as their cycloaddition to dimethyl acetylenedicarboxylate (DMAD) and dimethyl 2,3-dicyanobut-2- enedioate, were performed at the DFT B3LYP/6-31G(d) level of theory with the PCM solvation model. The calculations are in complete accordance with experimental results and explain the switch from the concerted to the non-concerted pathway depending on substituents in the dipolarophile and the ylide. It was found that strong electron-withdrawing substituents in dipolarophiles, such as in dialkyl dicyanobutenedioates, significantly reduce the barrier for the formation of zwitterionic intermediates in the reaction of azomethine ylides with such dipoles. This can render the stepwise cycloaddition competitive with the concerted one. However, the concertedness of the cycloaddition even to dipolarophiles with several electron-withdrawing substituents is governed by a fine balance of electronic and steric effects in both ylide and dipolarophile counterparts. The hypothesis that introduction of substituents in the azo- methine ylide that destabilize the positive charge in a corresponding zwitterion will favor the concerted cycloaddition even with dialkyl dicyanobutenedioates was tested theoretically and experimentally.

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Item Type:Journal Article, refereed, original work
Communities & Collections:07 Faculty of Science > Department of Chemistry
Dewey Decimal Classification:540 Chemistry
Language:English
Date:10 April 2014
Deposited On:16 Apr 2014 12:32
Last Modified:05 Apr 2016 17:49
Publisher:Wiley-Blackwell
ISSN:0018-019X
Funders:Russian Foundation for Basic Research (Grant No. 14-03-00187), Saint Petersburg State University (Grant No. 12.38.78.2012), National Science Center Cracow (Grant: Maestro-3, Dec-2012/06/A/ST-5/00219)
Publisher DOI:https://doi.org/10.1002/hlca.201300405

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