Synthesis of Quinoxalines via Ru/C Benzoin Oxidation and Diamine Condensation

Significance

Reported is the synthesis of quin­oxalines through the in situ oxidation of benzoins to 1,2-diketones and subsequent condensation with diamines. Although this reaction is not unknown, the oxidation system in this case used Ru/C, randomly methylated β-cyclodextrins (Ra-Me-β-CD), and an oxygen atmosphere with water as solvent (named as biomimetic conditions). For a reaction of 1 mmol of substrate, 300 mg of Ra-Me-β-CD was used. Ra-Me-β-CD was used to increase the dispersion of the supported ruthenium catalyst in water, thus increasing the activity of the catalyst. The oxidation does not proceed in the absence of Ra-Me-β-CD and evidence of complex formation between Ra-Me-β-CD and benzyl alcohol was obtained through NOESY studies.