Synthesis of Electron-Poor Coumarins from in situ Generated Stabilized Phosphorus Ylides in the Presence of Talc Powder in Solvent-free Conditions and Investigation of their Photochemical Reactions

Abstract

Protonation of the highly reactive 1:1 intermediates, produced in the reaction between triphenylphosphine and dialkyl acetylenedicarboxylates, by phenols (1-hydroxynaphthalene and 2-hydroxynaphthalene) leads to vinyltriphenylphosphonium salts, which undergo aromatic electrophilic substitution reaction with conjugate base to produce corresponding stabilized phosphorus ylides. Talc powder was found to catalyze conversion of the stabilized phosphorus ylides to coumarins in solvent-free conditions at 80-90ºC in 1 h in fairly high yields. Microwave was also found to catalyze the same reactions in the presence of talc powder in solvent-free conditions at microwave power 0.18-0.45 KW in 3 min. Photochemical reactions of the electron-poor coumarins were investigated.