Synthesis of 15-azayohimban, a new heterocyclic ring system

Article abstract of DOI:10.1016/S0040-4020(01)80944-3

Two synthetic routes to the 15-azayohimban ring system have been studied. The first one, based on a Pictet-Spengler condensation between tryptamine and piperidine acetal 4, gave very low yields of pentacycles 2a. The second, more efficient route involves as the crucial step a cyclization of a N-acyliminium cation generated from imide 11. The different course of the Pictet-Spengler reaction from amino acetals 4 and 8, as compared with amido acetal 7, is discussed.