Synthesis of 2-(9H-carbazol-1-yl)anilines from 2,3′-biindolyl and ketones

Noland WE, Brown CD, Zabronsky AE, Tritch KJ, Tetrahedron, 2018, 74, 2391-2404

Twenty-nine examples of 2-(9H-carbazol-1-yl)anilines were obtained in yields from 27 to 95% by refluxing 2,3′-biindolyl (1 equiv.) and ketones (1 equiv.) in ethanolic HCl. Alkyl, cyclic, and aryl ketones were found to be compatible with this method, however, aldehydes are not. Because the reaction proceeds by addition of the carbonyl C atom to the biindolyl 3-position, this method has high regioselectivity. One example is presented of bridging the two N atoms in the carbazolylaniline product with an acetaldehyde synthon to give a benzodiazepino[lm]carbazole. Also, one example is given of installing a dimethylamino group at the α-position of the starting ketone to give an indolo[3,2-c]carbazole.