Microwave-Assisted Direct Synthesis of 2-Substituted Benzoxazoles from Carboxylic Acids under Catalyst and Solvent-Free Conditions

A direct coupling of carboxylic acids with 2-aminophenol under microwave irradiation has been achieved leading to the synthesis of 2-substituted benzoxazoles under metal and solvent-free conditions. Aliphatic, aromatic and heteroaromatic carboxylic acids provide good yields. Benzoxazole formation takes place in the presence of chloro, methoxy, phenoxy, thiophenoxy, and (alpha),(beta)-unsaturated functionalities. In the case of dicarboxylic acids, the reaction proceeds via the formation of the corresponding anhydride with predominant formation of the mono-benzoxazole.