Synthesis of diazatricyclic common structure of madangamine alkaloids.

A general synthetic route toward a diazatricyclic core common to the madangamine family is described. Ring-closing metathesis and palladium-catalyzed cycloisomerization provided the cis-fused diazadecalin structure, accompanied by formation of the N-Boc-enamine, which was utilized as an N-acyliminium ion equivalent. Direct cyclization from the N-Boc-enamine was achieved through the in situ formation of an N,O-acetal.