Enantioselective Total Synthesis of (-)-Misramine

The enantioselective total synthesis of an unusual pentacyclic proaporphine alkaloid, (-)-misramine, was achieved. The synthetic strategy relied on an enantioselective intramolecular Friedel-Crafts-type 1,4-addition using an asymmetric organocatalyst to construct a spiroindane skeleton containing an all-carbon quaternary stereocenter and a double reductive amination of the keto-aldehyde to form a piperidine ring toward the end of the synthesis. This work is the first example of asymmetric synthesis of a proaporphine alkaloid.