Ormosia alkaloids. VII. Total synthesis of ormosanine, piptanthine, 18-epiormosanine, and d,l-panamine

Abstract

A stereoselective synthesis of ormosanine (1), identical in all respects with the naturally occurring racemic alkaloid of O. jamaicensis, has been accomplished. Subsequent transformation of synthetic ormosanine into racemic piptanthine (2) and into d,l-panamine (3) is described. 18-Epiormosanine (22) has also been prepared by total synthesis. Some unusual stereochemical effects allowing the control of configuration at C6, C11, and C18 are discussed.