Synthetic Efforts toward Lannotinidine G Based on an Aziridinium-Mediated Ring Contraction and Dienyne Metathesis

Lannotinidine G is a unique Lycopodium alkaloid that features a tricyclic [6/6/6] core with 3 contiguous stereocenters and a 1,3-diene moiety in addition to a 7-membered lactone. Herein, we disclose our efforts toward the synthesis of this natural product, which achieved the construction of the aza-tricyclic core with the correct configuration at its three stereocenters. Key features of our strategy include a highly diastereoselective Fráter-Seebach alkylation and Corey-Chaykovsky type epoxide formation, an unusual aziridinium-mediated ring contraction for the formation of the piperidine moiety, and a regioselective dienyne metathesis.