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

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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.