The reaction of the quinoxaline N‐oxide 1 with thiophene‐2‐carbaldehyde gave 6‐chloro‐2‐[1‐methyl‐2‐(2‐thienylmethylene)hydrazino]quinoxaline 4‐oxide 5, whose reaction with 2‐chloroacrylonitrile afforded 8‐chloro‐2,3‐dihydro‐4‐hydroxy‐1‐methyl‐3‐(2‐thienyl)‐1H‐1,2‐diazepino[3,4‐b]quinoxaline‐5‐carbonitrile 6. The reaction of compound 6 with various alcohols in the presence of a base effected alcoholysis to provide the 5‐alkoxy‐8‐chloro‐2,3,4,6‐tetrahydro‐1‐methyl‐4‐oxo‐3‐(2‐thienyl)‐1H‐1,2‐diazepino[3,4‐b]‐quinoxalines 7a‐d. The reaction of compounds 7a and 7b with diethyl azodicarboxylate effected dehydrogenation to give the 5‐alkoxy‐8‐chloro‐4,6‐dihydro‐1‐methyl‐4‐oxo‐3‐(2‐thienyl)‐1H‐1,2‐diazepino[3,4‐b]‐quinoxalines 8a and 8b, respectively. Compounds 8a and 8b were found to show good algicidal activities against Selenastrum capricornutum and Nitzchia closterium.

Synthesis of 1,2-Diazepino [3,4-b]quinoxalines by 1,3-Dipolar Cycloaddition Reaction and Their Ring Transformation to Pyridazino[3,4b]quinoxalines.-Seven compounds of type (V) and (VI) are prepared and tested for their antibacterial activities against six strains of bacteria. All compounds show inhibitory effects.

Synthesis of Novel 3-(2-Thienyl)-1,2-diazepino[3,4-b]quinoxalineswith Algicidal Activity. -The title compounds (VIII) show good algicidal activities against Selenastrum capricornutum and Nitzchia closterium. The preparation of various quinoxaline derivatives is reported.