Approach to cis-Phlegmarine Alkaloids via Stereodivergent Reduction: Total Synthesis of (+)-Serratezomine E and Putative Structure of (-)-Huperzine N.

A unified strategy for the synthesis of the cis-phlegmarine group of alkaloids is presented, leading to the first synthesis of serratezomine E (1) as well as the putative structure of huperzine N (2). A contrasteric hydrogenation method was developed based on the use of Wilkinson's catalyst, which allowed the facial selectivity of standard hydrogenation to be completely overturned. Calculations were performed to determine the mechanism, and structures for huperzines M and N are reassigned.