Deep eutectic solvent as solvent and catalyst: one-pot synthesis of 1,3-dinitropropanes via tandem Henry reaction/Michael addition

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

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 (DES). The five-membered-ring-formation products, the 2-arylbenzothiazoles, with a highest yield of 88%, were obtained by the reaction between 0.30 mmol of an o-aminothiophenol and 0.30 mmol of an α-phenylglyoxylic acid in choline chloride (ChCl)/d-(–)-tartaric acid DES at 60 °C for 0.5 h. The six-membered-ring-formation products, 3-aryl-2H-benzo[b][1,4]oxazin-2-one derivatives, were obtained in yields up to 99% by the reaction between 0.30 mmol of an o-aminophenol and 0.60 mmol of an α-phenylglyoxylic acid in ChCl/urea DES 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 DES at 70 °C for 1.5 h, the six-membered-ring-formation 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.