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.