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

摘要

1-Methyl-2-bromo-3-[(benzotriazol-1-yl)methyl]indole (2), available from the regio selective bromination of 1-methyl-3-[(benzotriazol-1-yl)methyl]in (1), undergoes halogen-lithium exchange with t-BuLi. The resulting carbanion 4 reacts with thiophene-3-carboxaldehyde, furan-3-carboxaldehyde, thiophene-2-carboxaldehyde, furan-2-carboxaldehyde, and indole-3-carboxaldehyde. Subsequent quenching with methyl iodide affords the corresponding methyl ether intermediates 6a-e in excellent yields. Refluxing intermediates 6a-e in 1,2,4-trichlorobenzene or 1,2-dichlorobenzene 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 31-67% yields. [References: 23]