Triphenylphosphine-Catalyzed Preparation of Sterically Congested, Electron-Poor N-Vinylimidazole Derivatives from Acetylenic Esters and Imidazole-Containing NH-Acids

Abstract

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and alkyl acetylenecarboxylates (or ethyl 3-phenyl-2-propynoate), by azathioprine or imidazole leads to vinyltriphenylphosphonium salts, which undergo a Michael addition reaction with a conjugate base to produce phosphorus ylides. Dipotassium hydrogen phosphate, potassium dihydrogen phosphate, and potassium iodide were found to catalyze the conversion of the phosphorus ylides to electron-poor N-vinyl imidazoles in solvent-free conditions under thermal (90°C, 1 h) conditions. The structural analysis of the products indicated that the reaction is regio- and stereoselective.

Keywords:

• Acetylenic esters
• dipotassium hydrogen phosphate
• electron-poor N-vinyl imidazoles
• potassium dihydrogen phosphate
• potassium iodide
• regioselective
• stereoselective
• vinyltriphenylphosphonium salt

Acknowledgments

This work was supported by the Zanjan University.