Abstract

Reactions of sterically congested stabilized phosphorus ylides with phenylhydrazine in the presence of silica gel powder in solvent-free conditions proceed smoothly at 100 ◦ C to afford dialkyl 2-(3,5-dimethyl-1-phenyl-1   H-pyrazol-4-yl)-2-butenedioates1H NMR,13C NMR spectra. The mass spectra of these compounds displayed molecularm/z values. The 1H NMR (CDCl3 ) spectra of the compoundsE and Z) for each pyrazoles. TheE and Z isomers were determined via their 1H NMR spectra in good yields. The structures of the products were deduced from their IR, and ion peaks at the appropriate show the presence of two estereoisomers ( relative population of The reaction is fairly stereoselective.