HMPA mediated one pot synthesis of 1-alkyl/aryl-4-dimethylamino[1,2,4]triazolo[4,3-a]quinoxalines

o-Phenylenediamine 1 is condensed with oxalic acid using Phillips' procedur e to obtain quinoxaline-2, 3-dione 2. The latter on treatment with hydrazin e hydrate gives the known 2-hydrazinoquinoxalin-3-one 3. Reaction of 3 with various acid chlorides (which were obtained from the corresponding carboxy lic acids by reaction with thionyl chloride in the presence of catalytic am ount of dimethyl formamide) in HMPA medium at 220 degreesC: in one pot reac tion yield the corresponding 1-substituted-4-dimethylamino[1, 2, 4]triazolo [4, 3-a]quinoxalines 4. This reaction has been shown to proceed through the intermediacy of 2-(N-acyl/aryl hydrazinoquinoxalin 3-one 5 and 1-substitut ed-4-oxo-[1, 2, 4] triazolo[4, 3-a]quinoxalines 6. An interesting observati on here has been that 5 can be cyclised to 6 at a considerably lower temper ature of 100 degrees than the requisite 220 degreesC using catalytic amount of HCl.