Expedient Construction of the [7-5-5] All-Carbon Tricyclic Core of the Daphniphyllum Alkaloids Daphnilongeranin B and Daphniyunnine D

A synthetic strategy for the construction of the [7-5-5] all-carbon tricyclic core of numerous calyciphylline A-type Daphniphyllum alkaloids has been developed using a key intramolecular Pauson-Khand reaction. A subsequent base-mediated double-bond migration and a regio- and stereoselective radical late stage allylic oxygenation provide access to the substitution patterns of daphnilongeranin B and daphniyunnine D.