Studies toward Total Synthesis of Non-aromatic Erythrina Alkaloids. (2). A General Method for Synthesis of Perhydro-6H-pyrido[2, 1-i]indole Derivatives : Synthesis of Isoerythroidine Skeleton

Abstract

A general method for synthesis of a physiologically important skeleton, perhydro-6H-pyrido[2, 1-i]indole, through cyclization of an active methylene group to an N-acyliminium, was developed. Treatment of the ketoester 5 with BF₃·Et₂O in methylene chloride resulted in deacetalization of the ethylene acetal group accomapnied with the expected double cyclization to give the tricyclic product 8 in 83% yield, and 8 was smoothly decarbomethoxylated to give decahydro-6H-pyrido[2, 1-i]indole-2, 6-dione (9). The former compound 8 was converted into derivatives of the isoerythroidine skeleton, 14 and 16.