Abstract
Oxidation of 1H-pyrazolo [3, 4-b] quinoxalines (1a : R=H, 1b : R=CH3) with m-chloroperbenzoic acid (MCPBA) gave the 4-oxides (2a, b). The structures of 2a, b were confirmed by synthesis, by condensing 2-chloroquinoxaline-3-carbaldehyde 4-oxide (6) with appropriate hydrazines. Further oxidation of 2a with MCPBA gave the 4, 9-dioxide (8). Treatment of 1, 2-dihydro-2-oxoquinoxaline-3-carboxamide (10) and 1, 2-dihydro-2-oxoquinoxaline-3-carbonitrile 4-oxide (13) with a mixture of POCl3 and PCl5 or POCl3-dimethyl-formamide afforded 2-chloroquinoxaline-3-carbonitrile (11) and its 4-oxide (14), respectively. When 11 and 14 were reacted with hydrazines, the corresponding 3-amino-1H-pyrazolo [3, 4-b]-quinoxalines (12a, b) and their 4-oxides (15a, b) were obtained in high yields. The reaction of ethyl 2-chloroquinoxaline-3-carboxylate (16) with hydrazine hydrate afforded a mixture of uncyclized products, N, N'-bis (2-ethoxycarbonyl-3-quinoxalinyl) hydrazine (17), ethyl 2-hydrazinoquinoxaline-3-carboxylate (18) and 2-hydrazinoquinoxaline-3-carbohydrazide (19).
