Heteropentalenes. The thermal addition of 1,3-dimethylpyrazolo-[1,2-a]benzotriazole to dimethyl acetylenedicarboxylate

Abstract

The title compound (3) reacts with dimethyl acetylenedicarboxylate with addition onto the azomethinimine moiety to give dimethyl 2a,4-dimethyl-4a,8b,8c-triazapentaleno[1,6-ab]indene-1,2-dicarboxylate (7)via a zwitterionic intermediate which can be trapped by protic solvents, e.g. methanol or water to give dimethyl 2-[o-(3,5-dimethylpyrazol-1-yl)anilino]-3-methoxymaleate (8) or tetramethyl 3,3′-bis-[o-(3,5-dimethylpyrazol-1-yl)anilino]-2,2′-oxydimaleate (9), respectively. The cycloadduct (7) undergoes spontaneous retrocycloaddition to dimethyl 3-methylpyrazolo[1,2-a]benzotriazole-1,2-dicarboxylate (12) and radical cleavage to yield, unexpectedly, methyl 4,5-dihydro-2-methyl-4-oxopyrazolo-[2,3-a]quinoxaline-3-carboxylate (17) as the main product together with small amounts of two benzotriazolypentenones (14) and (15).