Synthesis of novel benzo-1,2,5-thiadiazines, their antimicrobial activity and isomerization into benzo-1,2,4-triazines

Benzo[c]-6-aryl/alkylimino-1,2,5-thiadiazines (4a-g) have been obtained by the basification of benzo[c]-6-aryl/alkylimino-1,2,5-thiadiazine dihydroiodides (3a-g). The latter were synthesized by the oxidative cyclisation of substituted 1-aryl/alkyl- (3-(2'-aminophenyl)thiocarbamides (2a-g) by ethanolic iodine. Compounds (4a-g) on acylation with acetic anhydride and glacial acetic acid in 1 : 2 ratio afforded 2,5-diacetyl derivatives (5a-g), on reaction with sodium nitrite in 1 : 2 ratio in acidic medium afforded 2,5-dinitroso derivatives (6a-g) and on boiling with aqueous ethanolic sodium hydroxide solution isomerized into corresponding benzo-1,2,4-triazines (7a-g). The title compounds were assayed for their antimicrobial activity against gram-positive and gram-negative micro-organisms.