Condensed heterocyclic systems containing bridgehead nitrogen atom: Synthesis and bioactivity of thiazolo[3',2':2,3][1,2,4]triazino[5,6-b]indole and isomeric thiazolo[2',3':3,4][1,2,4]triazin[5,6-b]indole

9-Trifluoromethyl-5H-2,3-dihydro[1,2,4]triazino[5,6-b]indole-3-thione (2) on condensation with p-chlorophenacylbromide gives 5H-3-p-chlorophenacylmercapto-9-trifluoromethyl[1,2,4]triazino[5,6-b]indole hydrobromide (3) which on cyclization yields 3-p-chlorophenyl-6-trifluoromethylthiazolo[3',2':2,3][1,2,4]triazino[5,6-b]indole (4) and not the angular isomeric 1-(p-chlorophenyl)-6-trifluoromethylthiazolo[2',3':3,4][1,2,4]triazino[5,6-b]indole (6). The unequivocal synthesis of 6 has also been accomplished. The antibacterial and antifungal activity of 4 and 6 have been evaluated.