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Updated: Aug 2, 2025
Isolating Free Carbenes, their Mixed Dimers and Organic Radicals
Published on: April 19, 2019
Catalytic Asymmetric Cyclopropanations with Nonstabilized Carbenes
Kristen E Berger1, Raymond J Martinez1, Jianhan Zhou1
1Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, United States.
Abstract:
Cyclopropanes are common building blocks in pharmaceuticals, agrochemicals, and organic materials. The most general methods for the synthesis of chiral cyclopropanes are catalytic additions of diazoalkanes to alkenes. However, a limitation of this approach is that diazoalkanes can only be safely handled on preparative scales if they possess stabilizing substituents. Here we show that gem-dichloroalkanes can serve as precursors to nonstabilized carbenes for asymmetric cyclopropanation reactions of alkenes. The process uses a cobalt catalyst and is proposed to involve the formation of a cationic carbenoid species bearing structural resemblance to the Simmons-Smith reagent. High levels of enantioselectivity are observed for monosubstituted, 1,1-disubstituted, and internal alkenes. The reaction is compatible with alkyl-substituted carbenes, which are susceptible to undergoing competing 1,2-hydride shifts.
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