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

Chiral Lewis acid catalyzed asymmetric formation of cyclobutanones from α-silyloxyacroleins and α-alkyl or α-aryl diazoesters has been developed. In the presence of a chiral oxazaborolidinium ion catalyst, various α-silyloxycyclobutanones possessing a chiral β-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 γ-lactone, cyclobutanol, and cyclopentanone.