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

Abstract

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 α,β-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.

Key words

benzoxazole - carboxylic acid - 2-aminophenol - direct coupling - microwave - metal-free

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27

The work cited under ref. 14c deals with only three examples of benzoxazole formation by microwave-assisted condensation of aromatic carboxylic acids with 2-aminophenol.