Cycloadditions of indolizine-3-carbonitriles with dimethyl acetylenedicarboxylate: formation of [2.2.3]cyclazines and 1 : 2 adducts

Abstract

Reactions of indolizine-3-carbonitriles with dimethyl acetylenedicarboxylate (DMAD), in the presence of Pd–C, gave the corresponding [2.2.3]cyclazines in low to moderate yields, whereas, in the absence of Pd–C, the same reactions afforded the 1 : 2 molar products. The X-ray analysis of one of the 1 : 2 adducts established that the structure was dimethyl 2-cyano-3-styrylpyrrole-1,4-dicarboxylate. A possible mechanism is presented.