Asymmetric Synthesis of Cyclobutanone via Lewis Acid Catalyzed Tandem Cyclopropanation/Semipinacol Rearrangement

Chiral Lewis acid catalyzed asymmetric formation of cyclobutanones from alpha-silyloxyacroleins and alpha-alkyl or alpha-aryl diazoesters has been developed. In the presence of a chiral oxazaborolidinium ion catalyst, various alpha-silyloxycyclobutanones possessing a chiral, beta-quaternary center were synthesized in high yield (up to 91%) with excellent enantio- and diastereoselectivity (up to 98% ee and up to >20:1 dr) through tandem cyclopropanation/semipinacol rearrangement. The synthetic potential of this method was illustrated by conversion of the product to various cyclic compounds such as gamma-lactone, cyclobutanol, and cyclopentanone.