Rapid Construction of [5−6−7] Tricyclic Ring Skeleton of Calyciphylline Alkaloid Daphnilongeranin B

A concise photochemical [2 + 2] cycloaddition−Grob fragmentation sequence sets the common tricyclic ring skeletons of the Calyciphylline A-type alkaloids, particularly those in daphnilongeranins, daphniyunnines, and daphniglaucins.