Heterocyclic systems containing bridgehead nitrogen atom:: Synthesis and antimicrobial activity of a few heterocycles derived from 7-chloro-6-methyl-5H-2,3-dihydro-1,2,4-triazino [5,6-b] indole-3-thione

7-Chloro-6-methyl-5H-2,3-dihydro-1,2,4-triazino [5,6-b] indole-3-thione (11) on condensation with 1,2-dibromoethane, 1,3-dibromopropane and 2,3-dichloroquinoxaline gave the cyclized products 8-chloro-9-methyl-2,3-dihydro thiazolo [3',2'-2,3] [1,2,4] triazino [5,6-b] indole (III), 9-chloro-10-methyl-4H-2,3-dihydro [1,3] thiazlno [3',2':2,3] [1,2,4] triazino [5,6-b] indole (IV) and 10-chloro-11-methyl quinoxalino [2',3': 4,5] thiazolo [3,2b] indolo [2,3-e] [1,2,4] triazine (V) respectively and not the angular isomers VI, VII & VIII. The unequivocal synthesis of the latter (VI, VII & VIII) has been accomplished by. the reaction of 6-chloro-7-methylisatin-3-thiosemicarbazone (I) with 1,2-dibromoethane, 1,3-dibromopropane and 2,3-dichloroquinoxaline respectively. The antibacterial and antifungal activities of the synthesized compounds have been evaluated.