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■ 1,3-Dipolar Cycloaddition of Diazomethane to Differently Substituted 2-Methylpyridazin-3(2H)-ones

Francisco Fariña,* M. Victoria Martín, Magali Romañach, and Félix Sánchez

*Instituto de Química Orgánica General, C. S. I. C., Calle Juan de Cierva, 3, 28006 Madrid, Spain

Abstract

Cycloaddition of diaomethane to 4- or 5-substituted 2-methylpyridazin-3(2H)-ones 1,2 occurs in a practically regiospecific manner to give the expected adducts, which are not stable enough to be isolated and under the reaction conditions are transformed into N,N’-dimethylpyrazolopyridazinones and/or 2,4 (or 2,5)-dimethyipyridazin-3(2H)-ones, depending on the nature and position of the substituents. The regiochemistry of the cycloaddition and the reactivity of pyridazin-3 (2H)-ones 1,2 have been accounted for theoretically by the FMO approach.