Enantioselective Synthesis of 2-Aryl Cyclopentanones by Asymmetric Epoxidation and Epoxide Rearrangement

摘要

Optically active 2-aryl cycloalkanones are a class of useful molecules for organic synthesis and have received extensive attention. A number of effective approaches have been developed for the synthesis of 2-alkyl-2-aryl disubstituted cycloalkanones, including the Pd-catalyzed asymmetric -arylation of alkyl substituted cycloalkanones, the allylic alkylation of 2-aryl cycloalkanones, and the chelation-controlled Heck arylation of enol ethers. In the preparation of monosubstituted 2-aryl cycloalkanones, high ee values have also been obtained for 2-aryl cyclohexanones and cycloheptanones through the asymmetric protonation of the corresponding silyl enol ethers and enolates. Thus far, monosubstituted 2-aryl cyclopentanones are still a challenge to obtain, presumably because of facile racemization under the reaction conditions. Herein, we wish to report our preliminary efforts on the asymmetric epoxidation of benzylidenecyclobutane and subsequent epoxide rearrangement (Scheme 1).