Niobium-Catalyzed Coupling Reaction of α-Keto Acids with ortho-Phenylenediamines: Synthesis of 3-Arylquinoxalin-2(1H)-ones
A general methodology to access valuable 3-arylquinoxalin-2(1H)-ones was developed, by the reaction of α-keto acids with ortho-phenylenediamines in the presence of ammonium niobium oxalate (ANO) as a catalyst. The reactions were conducted in only 10 min under ultrasonic irradiation as an alternative energy source, affording water as the only co-product. A total of twenty-three different 3-arylquinoxalin-2(1H)-ones were selectively prepared in good to excellent yields by this atom-efficient protocol. Additionally, 1H-15N HMBC experiments were used to reveal the regioisomerism of the obtained products.