Lawesson’s Reagent and Microwaves: A New Efficient Access to Benzoxazoles and Benzothiazoles from Carboxylic Acids under Solvent-Free Conditions

Lawesson's reagent acts as an efficient promoter in the solvent-free microwave-assisted synthesis of 2-substituted benzoxazoles from carboxylic acids and 2-aminophenol, and thus, constitutes a general synthetic method for these compounds. This new application of Lawesson's reagent is valid also for benzothiazoles with very high efficiency level. A variety of aromatic, heteroaromatic and aliphatic carboxylic acids react under the conditions developed with good yields in all cases. Thiobenzoic acid is a good alternative for microwave-assisted synthesis of 2-phenylbenzoxazole and 2-phenylbenzothiazole in the absence of solvents.