Computational Insights into Different Mechanisms for Ag-, Cu-, and Pd-Catalyzed Cyclopropanation of Alkenes and Sulfonyl Hydrazones |
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Authors: | Dr Yong Wu Dr Shanshan Cao Dr Iskander Douair Prof Laurent Maron Prof Xihe Bi |
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Institution: | 1. Department of Chemistry, Northeast Normal University, Changchun, 130024 P.R. China
These authors contributed equally to this work.;2. INSA, UPS, UMR 5215, LPCNO, Université de Toulouse et CNRS, 135 Avenue de Rangueil, 31077 Toulouse, France;3. Department of Chemistry, Northeast Normal University, Changchun, 130024 P.R. China |
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Abstract: | The 2+1] cycloaddition reaction of a metal carbene with an alkene can produce important cyclopropane products for synthetic intermediates, materials, and pharmaceutical applications. However, this reaction is often accompanied by side reactions, such as coupling and self-coupling, so that the yield of the cyclopropanation product of non-silver transition-metal carbenes and hindered alkenes is generally lower than 50 %. To solve this problem, the addition of a low concentration of diazo compound (decomposition of sulfonyl hydrazones) to alkenes catalyzed by either CuOAc or PdCl2 was studied, but side reactions could still not be avoided. Interestingly, however, the yield of cyclopropanation products for such hindered alkenes were as high as 99 % with AgOTf as a catalyst. To explain this unexpected phenomenon, reaction pathways have been computed for four different catalysts by using DFT. By combining the results of these calculations with those obtained experimentally, it can be concluded that the efficiency of the silver catalyst is due to the barrierless concerted cycloaddition step and the kinetic inhibition of side reactions by a high concentration of alkene. |
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Keywords: | carbenes density functional calculations hindered alkenes reaction mechanisms silver |
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