1-Methylcarbazole-2,3-dicarboxylic acid dimethyl ester, a key intermediate in the synthesis of b-fused carbazoles, was successfully transformed into its 6-bromo and 6-nitro derivative via electrophilic substitution in acetic acid solution, using N-bromosuccinimide or urea nitrate, respectively, as reagents. With N-chlorosuccinimide, a 6,8-dichloro congener was also obtained in substantial amounts. The 6-substituted carbazolediesters were used as building blocks for the preparation of several new pyridazine- or pyrrole-fused carbazoles with basic side chains, featuring the core structure of previously developed antitumor compounds.
carbazoles; electrophilic substitution; bromination; nitration; antitumor activity
