Efficient synthesis of novel [1,3,4]thiadiazino[6,5-b]quinoxaline derivatives

Reaction of 2,3-dichloroquinoxaline with hydrazine and methylhydrazine gave 2-chloro-3-hydrazinyl quinoxaline and 2-chloro-3-(1-methylhydrazinyl) quinoxaline respectively in ethanol at room temperature. Condensation of 2-chloro-3-hydrazinyl quinoxaline and 2-chloro-3-(1-methylhydrazinyl) quinoxaline with carbon disulfide, trimethylamine and alkylhalides achieved a group of 3-(alkylsulfanyl) -1 H -[1,3,4]thiadiazino[6,5-b]quinoxaline and 1-methyl-3-(alkylsulfanyl)-1 H -[1,3,4]thiadiazino[6,5-b]quinoxaline respectively. Solvent effect of methanol and acetonitrile on this reaction and the spectral data is discussed. Fused [1,3,4]thiadiazines are a well known class of heterocycles. Among this class, [1,3,4]thiadiazino[6,5-b]quinoxaline have attracted less attention. There are a few routes for the preparation of this valuable compounds including; ring expansion of 3-amino-2-iminothiazolo[4,5-b]quinoxaline [1] and the cyclization of N -alkylazinium cations or 2,3-dichloroquinoxaline with bifunctional nuclephiles such as thiohydrazides and dithizone [2−4], which the last route utilized expensive reagents for the preparation of few derivatives.