Enantioselective Synthesis of γ-Hydroxyenones by Chiral Base-Catalyzed Kornblum DeLaMare Rearrangement

摘要

The first enantioselective Kornblum DeLaMare rearrangement based on the desymmetrization of meso-endoper-oxides by chiral base catalysis has been developed. A mechanism involving bifunctional catalysis of an E2-elimination is proposed and thus represents a rare example of cinchona-alkaloid catalyzed enantiodetermining deprotonation. The reaction is amenable to a variety of substrates providing an expedient entry into enantioen-riched γ-hydroxyenones from 1,3-dienes. This fact is exemplified by a one-pot asymmetric 1,4-dioxygenation of 1,3-cycloheptadiene (35) by sequential reaction with singlet oxygen and 5 mol % 11 providing γ-hydroxyenone 36 in 90% yield and 92% ee (eq 2).