Nitroacetic esters in the regioselective synthesis of isoxazole-3,5-dicarboxylic acids derivatives

An efficient and high-yielding strategy to prepare “unsymmetrical” 4-aryl-isoxazol-3,5-dicarboxylic acid derivatives from nitroacetic esters and aromatic aldehydes has been developed. The strategy is based on the isolation and usage of the previously missed intermediate of the Dornow reaction—5-hydroxy-6-oxo-4-aryl-6H-1,2-oxazine-3-carboxylates. In addition, the mechanism of the Dornow reaction was partially revised.