Rapid Construction of the ABC Ring System in the Daphniphyllum Alkaloid Daphniyunnine C

An efficient and scalable synthesis of the ABC ring system common to the calyciphylline A-type alkaloids has been developed. The tricyclic core of the alkaloids features a bowl-shaped [6-6-5] skeleton with five stereogenic centers including an all-carbon quaternary center. It was constructed rapidly from a readily available carvone derivative through a seven-step sequence involving an aza-Michael addition and Pd-catalyzed enolate α-vinylation as key steps.