Carcinogenic nitrogen compounds. Part LXXIV. Skraup and Combes–Beyer reactions with 3-aminocarbazoles; a new route to pyrido[3,2′b]carbazoles

Abstract

3-Amino-9-ethyl- and 3-amino-9-ethyl-6-methyl-carbazole follow Marckwald's rule in the Skraup reaction, to give derivatives of 7H-pyrido[2,3-c]carbazole; in contrast, the same amines undergo anti-Marckwald cyclisations in the Combes–Beyer reaction, to give derivatives of the linear 6H-pyrido[3,2-b]carbazole, which are analogues of the carcinostatic alkaloid ellipticine.