Synthesis of 3,3-diphenyl-3H-pyrazoles applying vinyl sulfones as chemical equivalents of acetylenes in reaction of 1,3-dipolar cycloaddition to diphenyldiazomethane

Abstract

Vinyl phenyl sulfone, methyl (E)-3-(phenylsulfonyl)- and methyl (E)-3-(p-tosyl)acrylates, (E)-3-(phenylsulfonyl)- and (E)-3-(p-tosyl)acrylonitriles react in ethyl ether at 20°C with diphenyldiazomethane leading to the formation of the corresponding 5,5-diphenyl-3-(arylsulfonyl)- Δ2-pyrazolines. Products containing a methoxycarbonyl or cyano group at treating with DBU in dichloromethane at 0°C suffer a dehydrosulfonation and are converted into 4-substituted 3,3-diphenyl-3H-pyrazoles. The oxidation of the mentioned Δ2-pyrazolines with activated manganese dioxide in benzene at 20°C leads to the formation of 4-methoxycarbonyl- and 4-cyano-substituted 5-arylsulfonyl- 3,3-diphenyl-3H-pyrazoles respectively. The reactions of α-bromovinyl phenyl sulfones and a-bromovinyl methyl sulfones with diphenyldiazomethane afforded the corresponding 3-bromo- 5,5-diphenyl-3-sulfonyl-Δ1-pyrazolines. The first among them at 20°C suffered spontaneous elimination of molecular nitrogen and converted into 1-bromo-2,2-diphenyl-1-(phenylsulfonyl)cyclopropane whose structure was established by X-ray diffraction analysis. The action of DBU on another Δ1-pyrazoline resulted in the formation of the product of the Ramberg–Backlund reaction, 5-methylene-3,3-diphenyl-Δ1- pyrazoline together with the product of hydrodebromination–isomerization, 5,5-diphenyl-3-(methylsulfonyl)- Δ2-pyrazoline.