Degradational cyclization of α-[2-phenyl-2- (phenylsulfonylhydrazono)ethyl]phenacylidenetriphenylphosphoranes to 3,6- diphenylpyridazines and 5-benzoyl-3-phenylpyrazoles

Article abstract of DOI:10.3987/COM-99-8733

α-[2-Phenyl-2- (phenylsulfonylhydrazono)ethyl]phenacylidenetriphenylphosphoranes were obtained (60-71%) by the reaction between phenylsulfonylhydrazones of phenacyl bromides and phenacylidenetriphenylphosphoranes. Thermolysis of the phosphoranes gave 3,6-diphenylpyridazines (43-66%) and 5-benzoyl-3- phenylpyrazoles (13-27%), together with triphenylphosphine oxide and S-phenyl benzenethiosulfonate, a disproportionation product from benzenesulfinic acid. The structure of the intermediate α-substituted phenacylidenetriphenylphosphorane was confirmed by an X-Ray diffraction method.