A GENERAL AND FACILE SYNTHESIS OF HETEROCYCLO[B]-FUSED CARBAZOLES

Methyl-2-bromo-3-[(benzotriazol-1-yl)methyl]indole (2), available from the regio selective bromination of 1-methyl-3-[(benzotriazol-1-yl)met hyl]in (1), undergoes halogen-lithium exchange with t-BuLi. The result ing carbanion 4 reacts with thiophene-3-carboxaldehyde, furan-3-carbox aldehyde, thiophene-2-carboxaldehyde, furan-2-carboxaldehyde, and indo le-3-carboxaldehyde. Subsequent quenching with methyl iodide affords t he corresponding methyl ether intermediates 6a-e in excellent yields. Refluxing intermediates 6a-e in 1,2,4-trichlorobenzene or 1,2-dichloro benzene causes intramolecular cyclization followed by aromatization. 5 -Methylthieno[3,2-b]carbazole (8a), 5-methylfuro[3,2-b]carbazole (8b), 5-methylthieno[2,3-b]carbazole (8c), 5-methylfuro[2,3-b]carbazole (8d ), and 5,11-dimethylindolo[3,2-b]carbazole (8e) are thus obtained in 3 1-67% yields.