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 alpha-vinylation as key steps.