Addition reactions of heterocyclic compounds. Part XXV. Dimethyl acetylenedicarboxylate with pyridazines and pyrazines

Abstract

Dimethyl acetylenedicarboxylate in acetonitrile with pyridazine, 3-methylpyridazine, and 1-methylphthalazine gave pyrido[1,2-b]pyridazines, with smaller amounts of related pyrrolo[1,2-b]pyridazines. 3,6-Dimethylpyridazine, however, gave mostly an azepino[1,2-b]pyridazine. 2-Methyl- and 2,6-dimethyl-pyrazines gave only low yields of pyrrolo[1,2-a]pyrazines under these conditions. In methanol, phthalazine gave 1,2-dihydro-1-methoxy-2-(1,2-dimethoxycarbonylvinyl)phthalazine, and phenazine gave 5,10-dihydro-5,10-di-(1,2-dimethoxycarbonylvinyl)phenazine. The nuclear magnetic resonance and ultraviolet absorption spectra of these adducts and their transformation products are discussed.