A divergent synthesis of dihydropyridazinones, N-substituted dihydropyrazoles, and O-substituted pyrazoles

Article abstract of DOI:10.1002/jhet.519

Dihydropyridazinones 4a,b, N-substituted dihydropyrazoles 5b-d, and O-substituted pyrazoles 6a-d have been synthesized starting from spirocyclopropanepyrazole derivative 2. Treatment of 2 with α-chloro esters, e.g., methyl chloroacetate, ethyl chloroacetate, isopropyl chloroacetate, and tert-butyl chloroacetate, in potassium carbonate/sodium iodide system caused ring opening and subsequent C- or N-attack nucleophilic substitution to give the corresponding dihydropyridazinones 4a,b and N-substituted dihydropyrazoles 5b-d. On the other hand, in the absence of sodium iodide, O-substituted pyrazoles 6a-d were obtained from 2 via an O-attack nucleophilic substitution.