Cyclopropanation of Electron-Rich Olefins with Fischer Carbenes

Significance

Prior to this study cyclopropanation reactions of Fischer carbene complexes and electron-rich alkenes required thermal conditions as well as high pressures of CO in order to suppress olefin metathesis. The authors now report a mild procedure involving the addition of acyclic and cyclic ketone lithium enolates to alkoxy Fischer carbene complexes of chromium under very mild reaction conditions. The resulting protected cyclopropanols are obtained in good yields as single diastereomers. Additionally, in the case of cyclic lithium enolates, a slight change in temperature selectively forms the corresponding bicyclic hydroxyl cyclobutanones as single diastereomers.