Studies on the syntheses of heterocyclic compounds—DLXIX : One-step synthesis of dihydropyridocarbazole derivatives

Heating indole and 4,5-dibromomethyl-3-hydroxy-2-methylpyridine hydrobromide (10), followed by acetylation, gave the desired dihydropyrido[4.3-b]carbazole (12) and its structural isomer, dihydropyrido[3.4-b]carbazole (13). The structures of (12 and 13) were determined by UV spectral investigations of the corresponding dehydrogenated products, 4-acetoxy-3-methyl-6H-pyrido[4.3-b]carbazole (11) and 4-acetoxy-3-methyl-10H-pyrido[3.4-b]carbazole (14).On the other hand, the same reaction in the presence of sodium iodide afforded 12 together with four other coupling products which were not cyclized, such as (16, 17, 18), and a dimer.