Niobium-promoted reaction of α-phenylglyoxylic acid with ortho-functionalized anilines: synthesis of 2-arylbenzothiazoles and 3-aryl-2H-benzo[b][1,4]benzoxazin-2-onesElectronic supplementary information (ESI) available: Detailed experimental procedures and figures of NMR spectra. See DOI: 10.1039/c6gc02495e

A new and general method to prepare 2-arylbenzothiazoles and 3-aryl-2 H -benzo[ b ][1,4]benzoxazin-2-ones by the reaction of α-arylglyoxylic acid with o -aminothiophenol and o -aminophenol respectively is described. The use of ammonium niobium oxalate (ANO) as the catalyst and PEG-400 as the solvent were crucial to afford the title compounds in good yields and selectivity. The reaction time can be reduced from hours to few minutes when ultrasound is used as an alternative energy source. Ammonium niobium oxalate promotes the reaction of α-phenylglyoxylic acid with o -functionalized anilines for the synthesis of benzothiazoles and benzoxazin-2-ones.