A General and Facile Synthesis of Heterocyclo-Fused Carbazoles

Article abstract of DOI:10.1021/jo00117a022

1-Methyl-2-bromo-3-<(benzotriazol-1-yl)methyl>indole (2), available from the regioselective bromination of 1-methyl-3-<(benzotriazol-1-yl)methyl>indole (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 31-67percent yields.