1,3-dipolar cycloaddition of diazoalkanes to racemic and optically active α-(diethoxyphosphoryl)vinyl p-tolyl sulfoxides: A new synthesis of 3- phosphorylpyrazoles and asymmetric synthesis of cyclopropanes

Article abstract of DOI:10.1016/S0040-4020(99)00943-6

Cycloaddition of diazomethane and ethyl diazoacetate to α- (diethoxyphosphoryl)vinyl p-tolyl sulfoxide 1a and its β-substituted analogues (Me, Ph) results in the formation of 3-phosphorylpyrazoles in high yield. The reaction of chiral (S)-(+)-1a with diphenyldiazomethane proceeds fully diastereoselectively to give the corresponding cyclopropane (+)-6a with the (S(C), S(S)) configuration determined by X-ray diffraction analysis. Diazopropane reacts with (S)-(+)-1a to give only one diastereoisomer of the pyrazoline cycloadduct (+)-2e which undergoes decomposition to the cyclopropane (+)-6b with preservation of configurational integrity.