Three Questionable Cases in the Chemistry of Quinoxalines and Benzodiazepines in the Way of the Syntheses of Benzimidazoles

The reaction of 3-ethoxycarbonylmethylene-3,4-dihydroquinoxalin-2(1H)-one with the Vilsmeier reagent, the treatment of 3-(3,4-dihydroquinoxalin-2(1H)-on-3-yl)-1,2-dihydro-1,5-benzodiazepin-2(1H)-one hydrochloride with 10% sodium hydroxide and 3-benzimidazoylquinoxaline-2(1H)-one with both 1,2-phenylenediamine dihydrochloride, and the reactions of 1,2-phenylenediamine have been reinvestigated, and the structures of these reaction products have been revised. The aforementioned reactions have been shown to proceed with the formation of 1-N,N-dimethylaminomethylene-2-oxo-1,2-dihydrofuro[2,3-b]quinoxaline in the first case, the formation of 3-[2-(benzimidazol-2-on-1-yl)vinyl]-1H-quinoxalin-2-one in the second case, and the formation of 2,3-bis-(1H-benzimidazol-2-yl)quinoxaline in the third case and not the formation of 3-(N,N-dimethylaminocarbonyl)furo[2,3-b]quinoxaline hydrochloride , the free base of 3-(3,4-dihydroquinoxalin-2(1H)-on-3-yl)-1,2-dihydro-1,5-benzodiazepin-2(1H)-one , that is, compound and benzodiazepine derivative , as has been described earlier. In the third case, the formation of 2,3-bis-(1H-benzimidazol-2-yl)quinoxaline occurs according to the novel quinoxalin-2(1H)-one benzimidazole rearrangement discovered by us. The potential mechanisms for the investigated reactions are discussed.