Dipotassium Hydrogen Phosphate Powder-Catalyzed Stereoselective Synthesis of N-Vinyl Pyrazoles in Solvent-Free Conditions

Abstract

Protonation of the highly reactive 1:1 intermediates, which are produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by 3,5-dimethylpyrazol leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce dialkyl 2-(3,5-dimethyl1H-pyrazol-1-yl)-3-(triphenylphosphoranylidene)butanedioates. Dipotassium hydrogen phosphate powder was found to catalyze the stereoselective conversion of dialkyl 2-(3,5-dimethyl-1H-pyrazol-1-yl)-3-(triphenylphosphoranylidene) butanedioates to dialkyl 2-(3,5-dimethyl-1H-pyrazol-1-yl)-2-butenedioates in solvent-free conditions under microwave (0.6 KW, 3 min) and thermal (90°C, 60 min) conditions.

Keywordse:

• 3,5-dimethylpyrazol
• acetylenic esters
• dipotassium hydrogen phosphate
• Michael addition
• microwave irradiation
• vinyltriphenylphosphonium salt