Synthesis of the ABCDG ring skeleton of communesin F based on carboborylation of 1,3-diene and Bi(OTf)₃-catalyzed cyclizations

Communesins, isolated from the mycelium of a strain of Penicillium sp., are cytotoxic heptacyclic indole alkaloids bearing a bis-aminal structure and two contiguous quaternary carbon centers. Toward a total synthesis of communesin F, we synthesized a pentacyclic ABCDG ring skeleton via carboborylation of 1, 3-diene and a Friedel–Crafts-type cyclization, resulting in the formation of an azepine ring through a Bi(OTf)₃-catalyzed SN2’ reaction.