Direct Construction of 1,4-Dihydropyridazines and Pyrazoles via Annulation of Alkyl 2-Aroyl-1-chlorocyclopropanecarboxylates.

An efficient and chemodivergent synthesis of highly functionalized 1,4-dihydropyridazines and pyrazoles has been accomplished via base-promoted annulation between hydrazones and alkyl 2-aroyl-1-chlorocyclopropanecarboxylates, respectively. This transition-metal-free domino reaction proceeded rapidly under mild basic conditions, affording potentially bioactive 1,4-dihydropyridazine and pyrazole derivatives in moderate yields. The conversion of 1,4-dihydropyridazine to pyrazole was confirmed by adjusting the quantity of the base.