Dimethyl acetylenedicarboxylate reacts with 6-methyl-2-phenyl- and -2-cyclohexyl-tetrahydropyridazin-3-ones (7) and (8) to give 1-anilino- and 1-cyclohexylamino-tetrahydroazepin-4-ones (10) and (11). No maleate ester derivatives, such as the oxopyrazolidinylmaleate (4) formed when 2-benzyl-5-methylpyrazolidin-3-one (2) reacts with the ester, are obtained with the pyridazinones. 6-Methyl-2-phenyltetrahydropyridazin-3-one (7) undergoes photochemical ring contraction to 1-anilino-5-methylpyrrolidin-2-one (12).
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Eǧe et al. (1977) studied this question.