Regioselective hydrolysis of dimethyl 1-methyl-9H-carbazole-2,3-dicarboxylate permits functionalisation of the carbazole skeleton in position 3 by conversion of the carboxylic acid 2 thus obtained into the azide 3. Curtius degradation of the latter gives the amine 5, various urethane derivatives thereof (4), and the urea 6. Base-induced cyclization of 6 leads to the pyrimido[5,4-b]carbazole 7a, whereas an analogous compound bearing a basic side chain (7b) is formed by spontaneous cyclization of an intermediate urea.