Condensed bridgehead nitrogen heterocyclic systems:: Synthesis and bioactivity of 2,3-dihydrothiazolo[3′,2′ : 2,3]-as-triazino[5,6-b] indole, 2,3-dihydro-4H-[1,3]thiazino[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-8-isopropyl-5H-as-triazino[5,6-b]indole-3-thione 2 on condensation with 1,2-dibromoethane, 1-3-dibromopropane and 2,3-dichloroquinoxaline gives the cyclized products, 7-isopropyl-2,3-dihydrothiazolo[3',2':2,3]-as-triazino[5,6-b] indole 3, 2,3-dihydro-8-isopropyl-4H-[1,3]thiazino[3',2':2,3]-as-triazino[5,6-b]indole 4 and 9-isopropylquinoxalino[2',3' : 4,5]thiazolo[3,2-b]indolo[2,3-e]-as-triazine 5, respectively and not the angular isomers, 7-isopropyl-2,3-dihydro[2',3':3,4]as-triazino[5,6-b]indole 6, 8-isopropyl-1H-2,3-dihydro[1,3]thiazino[2',3':3,4]-as-triazino[5,6-b]indole 7 and 3-isopropylquinoxalino [2',3':4,5]thiazolo[2,3-c]indolo[2,3-e]-cis-triazine 8. The unequivocal synthesis of the latter 6, 7 and 8 has been accomplished by reaction of 5-isopropylisatin-3-thiosemicarbazone 1 with 1,2-dibromoethane, 1,3-dibromopropane and 2,3-dichloroquinoxaline, respectively. The bioactivity of the synthesized compounds have also been evaluated.