Reaction between 3H-pyrrolizines and acetylenedicarboxylic esters. Part II. Preparation of derivatives of cycl[4,2,2]azine (azepino[2,1,7-cd]pyrrolizine)

Abstract

Reaction between 3H-pyrrolizines and an excess of dimethyl acetyfenedicarboxylate gave 6,7-dihydro-5H-azepino[2,1,7-cd]pyrrolizine-5,6,7,8-tetracarboxylic esters (4)–(6); diethyl acetylenedicarboxylate gave only one analogous product (7). The 6,7-dihydro-5H-azepinopyrrolizine (4) was readily dehydrogenated to give the 5H-azepinopyrrolizinetetracarboxylate (9), which was stable towards oxidising agents. An intermediate in the production of the 3,4-dimethyldihydroazepinopyrrolizine (6) has been isolated and shown to be the pyrroliziri-3,5-diyldimaleate (11). A mechanism is proposed for the formation of the dihydroazepinopyrrolizines.