Unified Asymmetric Hydrogenation Enables Stereocontrolled Total Synthesis of Tacaman Alkaloids

The subgram-scale total synthesis of the tacaman alkaloids (-)-tacamine, (+)-tacamonine, (+)-17-β-hydroxytacamonine, and (-)-decarbomethoxytacamine is reported. Our approach prominently features a unified, highly enantioselective Ir-catalyzed hydrogenation of Wenkert's enamide analogues. This method enables the construction of a series of cis-fused indoloquinolizidine scaffolds with exceptional reaction efficiency and enantioselectivities, achieving yields of up to 98% and enantiomeric excesses (ee) of up to 99%.