Improved Syntheses of Substituted Carbazoles and Benzocarbazoles via Lithiation of the (Dialkylamino)methyl (Aminal)Derivatives

Article abstract of DOI:10.1021/jo00239a020

The lithiation of N-<(dialkylamino)methyl>carbazoles occurs readily and exclusively at the protonated carbon adjacent to the nitrogen atom.Reaction with a variety of electrophiles produces good to excellent yields of monosubstituted derivatives.Removal of the lithio-directing and nitrogen-protecting function is readily achieved by mild acid-catalyzed hydrolysis during workup of the reaction.Thus, carbazole undergoes lithiation at the 1-position, dibenzocarbazole at the analogous 6-position, and benzocarbazole at both the 6-and 8-positions, with the former predominating. 1,2,3,4-Tetrahydrocarbazole undergoes lithiation at the 8-position, but with 2,3-dimethylindole reaction occurs at the 2-methyl group.Benzocarbazole fails to form an aminal derivative, but on direct lithiation in ether it can be substituted exclusively at the 1-position of the fused benzene ring.