Triphenylphosphine Catalyzed Stereoselective Addition of 3,5-Diphenyl-1H-pyrazole to Acetylenic Esters

Abstract

Protonation of the highly reactive 1:1 intermediates produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates by 3,5-diphenyl-1H-pyrazole leads to vinyltriphenylphosphonium salts. The cation in these salts undergoes an addition reaction with the counter anion in CH ₂ Cl ₂ at room temperature to yield the corresponding stabilized phosphorus ylides. Elimination of triphenylphosphine from the stabilized phosphorus ylides leads to the corresponding electron-poor N-vinyl pyrazoles in fairly high yields. The reaction is fairly stereoselective.

Keywords:

• Catalyst
• dialkyl acetylenedicarboxylates
• electron-poor N-vinyl pyrazoles
• phosphorus ylide
• triphenylphosphine
• vinyltriphenylphosphonium salts

Acknowledgments

This work was supported by the Sandoogh Hemayate as Pajuoheshgharane Keshvare Iran.