Facile Metal-Free Synthesis of 3-Aryl-4-Substituted Coumarins from O-Hydroxy Carbonyl Compounds

Abstract

The intramolecular cyclization of the esters of salicylaldehyde, O-hydroxyacetophenones, methyl salicylate, and 2′-hydroxy chalcones by potassium hydroxide in pyridine leads to a short and convenient synthesis of 3,4-disubstituted coumarins. Twenty 3-phenyl coumarins were synthesized in 80–90% yields. No other by-product, such as 2-benzylchromone or β-diketones, was observed the reactions. The mild reaction condition involves the removal of more acidic benzylic proton, which leads to a relatively cheap, nontoxic, metal-free method for the synthesis of 3-aryl-4-substituted coumarins.