The Reaction of Phenylhydrazine with Sterically Congested Stabilized Phosphorus Ylides in the Presence of Silica Gel Powder in Solvent-Free Conditions: A Novel Synthesis of Fully Substituted Pyrazole Derivatives

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-1H-pyrazol-4-yl)-2-butenedioates in good yields. The structures of the products were deduced from their IR, ¹ H NMR, and ¹³ C NMR spectra. The mass spectra of these compounds displayed molecular ion peaks at the appropriate z values. The ¹ H NMR (CDCl ₃ ) spectra of the compounds show the presence of two estereoisomers (E and Z) for each pyrazoles. The relative population of E and Z isomers were determined via their ¹ H NMR spectra The reaction is fairly stereoselective.

Keywords:

• Phenylhydrazine
• phosphorus ylide
• pyrazole
• silica gel
• solvent-free conditions

Acknowledgments

This work was supported by the Zanjan University.