Catalytic Enantioselective Pinacol and Meinwald Rearrangements for the Construction of Quaternary Stereocenters

The
development of enantioselective pinacol rearrangement is extremely
challenging due to the likelihood involvement of the carbenium intermediate
that renders the stereochemical communication between catalyst and
substrate difficult to achieve. Herein, we report chiral N-triflyl phosphoramide-catalyzed enantioselective pinacol rearrangement
of 1,2-tertiary diols and mechanistically related Meinwald rearrangement
of tetrasubstituted epoxides for the synthesis of enantioenriched
2-alkynyl-2-arylcyclohexanones and 2,2-diarylcyclohexanones, respectively.
Total synthesis of (+)-mesembrane featuring the catalytic enantioselective
pinacol rearrangement as a key strategic step is also documented.