Chiral Synthesis of Erythrina Alkaloids. I. Total Synthesis of (+)-Erysotrine via Asymmetric Diels-Alder Reaction under High Pressure

Abstract

(S)- (+)-3,4-Dimethoxyphenylalanine methyl ester (lb) was converted, in 3 steps, into (5S)-(-)-8,9-dimethoxy-1,5-dimethoxycarbonyl-2,3-dioxo-2,3,5,6-tetrahydropyrrolo[2,1 -a]isoquinoline (2b). Diels-Alder reaction of 2b with l-methoxy-3-trimethylsilyloxybutadiene under extremely high pressure (10 kbar), followed by desilylation, gave moderate yields of erythrinan derivatives (11), which were converted, in several steps, into (+)-erysotramidine (23b) and (+)-erysotrine (4), thus accomplishing the first total synthesis of natural Erythrina alkaloids in chiral forms. © 1993, The Pharmaceutical Society of Japan. All rights reserved.