Reaction between 3H-pyrrolizines and acetylenedicarboxylic esters. Part I. Preparation of 3-(alkoxycarbonylmethylene)-3H-pyrrolizines

Abstract

3H-Pyrrolizine reacts with dimethyl ordiethylacetylenedicarboxylate to give the 3-[alkoxycarbonyl(alkoxycarbonyl-methyl)methylene]-3H-pyrrolizines (5) and (8). 1-Methyl-3H-pyrrolizine and 6,7-dimethylpyrrolizine give the similar compounds (6) and (7) with the dimethyl ester; with the diethyl ester 1-methyl-3H-pyrrolizine gives a 3H-pyrrolizin-5-ylmaleate (13) shown to be an intermediate in the production of the expected compound (10). A mechanism for the reaction has been proposed, and tested by deuterium-labelling experiments. 3-Diphenyl-methylene-3H-pyrrolizine undergoes cycloaddition with dimethyl acetylenedicarboxylate to give a dihydrocycl-[3,2,2]azine (dimethyl 5,6-dihydro-5,5-diphenylpyrrolo[2,1,-cd]indolizine-6,7-dicarboxylate)(14).