Nucleophilic ring-opening reactions of trans-2-aroyl-3-aryl-cyclopropane-1,1-dicarboxylates with hydrazines.

trans-2-Aroyl-3-aryl-cyclopropane-1,1-dicarboxylates when treated with arylhydrazines in refluxing EtOH gave dihydropyrazoles, whereas with hydrazines in refluxing AcOH, they formed cyclopropane-fused pyridazinones. Although in both cases the corresponding hydrazones are formed initially, the former case involves a subsequent 5-exo-tet nucleophilic ring-opening, and the later, a 6-exo-trig nucleophilic attack by the other hydrazone nitrogen. The products are obtained in moderate to excellent yields with complete regio-and diastereoselectivity.