General and efficient strategy for erythrinan and homoerythrinan alkaloids: Syntheses of (±)-3-demethoxyerythratidinone and (±)- erysotramidine

A general and efficient strategy to both aromatic-type and nonaromatic-type erythrinan and homoerythrinan alkaloids has been developed. This approach involves a key two-step sequence, an alkylation of a ketone with various N-substituted iodoacetamides followed by a N-acyliminium ion promoted intramolecular cyclization, and represents one of the shortest routes to erythrinan and homoerythrinan alkaloids. As the application, the formal total synthesis of (±)-3-demethoxyerythratidinone and the total synthesis of (±)-erysotramidine have been achieved, respectively.