Synthesis of novel 3-(2-thienyl)-1,2-diazepino[3,4-b]quinoxalines with algicidal activity

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-tetmhydro-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.