Enantioselective Cyclopropanation/[1,5]-Hydrogen Shift to Access Rauhut-Currier Product.

A Michael addition initiated cyclopropanation/[1,5]-hydrogen shift has been developed for the enantioselective synthesis of Rauhut-Currier products. The reaction of α-alkyl diazoesters and in situ generated -quinone methides proceeds in the presence of chiral oxazaborolidinium ion, providing -stereocontrolled Rauhut-Currier products in high yields (up to 96%) with excellent / selectivities (>20:1) and enantioselectivities (up to >99% ee). The synthetic utility was illustrated by conversion of the product to 3,4-dihydrocoumarins with two adjacent chiral stereocenters.