Synthesis of 2H-1,2,3-triazole-4-carboxylic acids via Ru(II)-catalyzed rearrangement of 4-hydrazonoisoxazol-5-ones

An atom-economy, two-step synthesis of 2H-1,2,3-triazole-4-carboxylic acids from 3-arylisoxazol-5(4H)-ones and arenediazonium tetrafluoroborates is described. The formation of the 1,2,3-triazole ring is achieved by the [Ru(p-cymene)Cl2]2-catalyzed rearrangement of 4-hydrazonoisoxazol-5-ones which are resulted from the diazo coupling. The advantages of the method include the available starting compounds and the ability to purify target acids without the use of chromatography.