Protecting-Group-Free Enantioselective Synthesis of (-)-Pallavicinin and (+)-Neopallavicinin.

Abstract

The first enantioselective synthesis of (-)-pallavicinin and (+)-neopallavicinin has been achieved in 15 steps. The described synthesis avoids protecting-group manipulations by synthesis designs predicated on highly chemo- and stereoselective transformations. Highlights of the synthesis include a palladium-catalyzed enantioselective decarboxylative allylation to form the chiral all-carbon quaternary stereocenter, a palladium-catalyzed oxidative cyclization to assemble the [3.2.1]-bicyclic moiety, and an unprecedented LiBHEt3-induced fragmentation/protonation of an α-hydroxy epoxide to form the α-furan ketone with the desired configuration.