Kaolinite Powder as an Efficient Catalyst for the Preparation of Coumarins from in Situ Generated Stabilized Phosphorus Ylides in Solvent-free Conditions

Abstract

Protonation of the highly reactive 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. Kaolinite powder was found to catalyze conversion of the stabilized phosphorus ylides to coumarins in solvent-free conditions at 80-90°C in 1 h in fairly high yields. Microwave also was found to catalyze the same reactions in the presence of kaolinite powder in solvent-free conditions at microwave power 0.18-0.45 kW in 3 min.