Enantioselective Total Synthesis and Absolute Configuration Assignment of (+)-Tronocarpine Enabled by an Asymmetric Michael/Aldol Reaction.

We present the first asymmetric total synthesis and absolute configuration determination of (+)-tronocarpine. The [6.5.7.6.6] pentacyclic core was constructed at an early stage by using a sequential cyclization strategy through a newly developed catalytic asymmetric Michael/aldol cascade to build the aza[3.3.1]-bridged cycle and a tandem reduction/hemiamidation procedure to assemble the seven-membered lactam. The side-chain functionalities were incorporated at a late stage by several appropriately orchestrated manipulations under mild conditions. The synthesis of enantiomerically pure (+)-tronocarpine was achieved through a 20-step longest linear sequence from tryptamine.