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.

The dicarbonyl diazo reagents α-ketodiazoacetates (KDA) represent one type of acceptor/acceptor-substituted diazo reagents that have not been effectively utilized for asymmetric cyclopropanation (Scheme 1). This catalytic process would be highly attractive as the resulting chiral 1, 1-cyclopropaneketoesters, which bear both ketone and ester functionalities, can serve as versatile synthons for a wide range of useful asymmetric transformations. In addition to their ready conversion to chiral cyclopropane derivatives having different geminal functionalities,[5a, 10] 1, 1-cyclopropaneketoesters can be transformed to other valuable chiral molecules through various ring-opening and ring-expanding reactions, which are greatly facilitated by the presence of two electron-withdrawing groups at the geminal position (Scheme 1).[1c, 1d, 3b] While its non-asymmetric protocols have already been fruitfully applied to natural product synthesis,[11] there have been only a few previous reports on catalytic systems for asymmetric cyclopropanation with KDA.[5a, 12, 13] Among them, the most notable example is the Rh2-based system developed recently by Charette and coworkers.[5a] It was shown that the PMP-substituted KDA could be successfully used for asymmetric cyclopropanation, producing the corresponding (Z)-1, 1-cyclopropaneketoesters