Asymmetric Formal Synthesis of (-)-Cephalotaxine via Palladium-Catalyzed Enantioselective Tsuji Allylation.

Asymmetric synthesis of the pentacyclic alkaloid (-)-cephalotaxine was accomplished via palladium-catalyzed enantioselective Tsuji allylation for construction of the aza-containing tetrasubstituted stereogenic center (95% yield, 93% ee). The allyl enol carbonate precursor was prepared from Hanaoka's ketone intermediate, which was formed by a novel formic acid promoted ring-expansion reaction.