Cobalt(II)‐Catalyzed Asymmetric Olefin Cyclopropanation with α‐Ketodiazoacetates

Abstract

Cyclopropanes are a unique class of structure elements found in a number of biologically important compounds and have been demonstrated for a wide range of fundamental and practical applications.[1] One particularly attractive strategy for enantioselective synthesis of chiral cyclopropanes is based on transition metal-catalyzed asymmetric olefin cyclopropanation with diazo reagents.[2] In principle, chiral cyclopropane derivatives with all substitution patterns may be accessible in enantioenriched form by asymmetric cyclopropanation due to the diverse availability of both alkenes and diazo reagents. Among different classes of diazo reagents with various combinations of α-substituents, many acceptor- and donor/acceptor-substituted diazo reagents have been successfully employed as effective carbene sources for metal-catalyzed asymmetric cyclopropanation.[2] In contrast, the capacity of catalytic asymmetric cyclopropanation has not been fully explored with acceptor/acceptor-substituted diazo reagents, which would afford synthetically useful cyclopropane compounds bearing geminal electron-withdrawing functionalities.[3,4] Although there have been some recent successes in this area,[5–9] several important types of acceptor/acceptor-substituted diazo reagents remain challenging for asymmetric olefin cyclopropanation.