Reactions of α-Phenylglyoxylic Acids with ortho-Functionalized Anilines in Deep Eutectic Solvents: Selective Syntheses of 3-Aryl-2H-benzo[b][1,4]oxazin-2-ones, 2-Arylbenzothiazoles, and 3-Arylquinoxalin-2(1H)-ones

Abstract

α-Phenylglyoxylic acid is a novel cyclization reagent. In this study, three cyclization products were synthesized by the reaction of α-phenylglyoxylic acids with ortho-functionalized anilines in deep eutectic solvents. The five-membered ring products synthesized using 2-arylbenzothiazole displayed the highest yield of 88 %, obtained by the reaction between 0.30 mmol of o-aminothiophenol and 0.30 mmol of α-phenylglyoxylic acid in choline chloride (ChCl)/D(–)-tartaric acid deep eutectic solvent at 60 °C for 0.5 h. The six-membered ring products synthesized using 3-aryl-2H-benzo[b][1,4]oxazin-2-one derivatives in ChCl/urea deep eutectic solvent displayed a yield of 99 %, obtained by the reaction between 0.30 mmol of an o-aminophenol and 0.60 mmol of an α-phenylglyoxylic acid at 80 °C for 2.0 h. In the reaction between 0.30 mmol of o-phenylenediamine and 0.45 mmol of an α-phenylglyoxylic acid in ChCl/anhydrous tin(II) chloride deep eutectic solvent at 70 °C for 1.5 h, the six-membered ring products, 3-arylquinoxalin-2(1H)-one derivatives, were synthesized, with a highest yield of 96 %. This cyclization reaction occurred without the addition of other catalysts, and the title compounds were obtained with good yields under mild conditions.