Bridgehead nitrogen heterocyclic systems:: Synthesis and evaluation of biological activity of 2,3-dihydrothiazolo[3′,2′:2 3]-as-triazino[5,6-b] indole and quinoxalino[2′,3′:4,5]thiazolo[3,2-b]indolo[2,3-e]-as-triazine and their isomeric systems.

2, 3-Dihydro-6-ethyl-5H-as-triazino[5, 6-b]indole-3-thione 2, on condensation with 1, 2-dibromoethane and 2, 3-dichloroquinoxaline gives the cyclized products, 9-ethyldihydrothiazolo[3', 2':2, 3]-as-triazino[5, 6-b]indole hydrobromide 4 and 11-ethyl quinoxalino[2', 3':4, 5]thiazolo[3, 2-b]indolo[2, 3-e]-as-triazine 6 respectively and not the angular isomers,.2, 3-dihydro-9-ethyl-1H-[1, 3]thiazolo[2', 3':3, 4]-as-triazino[5, 6-b]indole hydrobromide 3 and 1-ethylquinoxalino [2', 3':4, 5]thiazolo[2,'3-c]indolo[2, 3-e]-as-triazine 5. The unequivocal synthesis of the latter 3 and 5 has been accomplished by reaction of 7-Ethylisatin-3-thiosemicarbazone 1 with 1, 2-dibromoethane and 2, 3-dichloroquinoxaline, respectively.. The. antibacterial and antifungal activity of the synthesized compounds have also been evaluated.