Pyrrole studies. Part 32. A novel ring-cleavage reaction of the pyridazine ring during the reaction of 6H-pyrrolo[3,4-d]pyridazines with dimethyl acetylenedicarboxylate

Abstract

The reaction of 6H-pyrrolo[3,4-d]pyridazines with dimethyl acetylenedicarboxylate in methanol leads initially to (1,2-dihydro-1-methoxy-6H-pyrrolo[3,4-d]pyridazin-2-yl)fumaric esters, which are unstable in the presence of water and undergo a ring-cleavage reaction to yield 4,5-diaza-6-pyrrol-3-ylhexa-3,5-dienoates. The structure of the 4-formyl-2,5-dimethylpyrrol-3-yl derivative has been confirmed by X-ray crystallography.