Studies on intramolecular nh‐bridging in aromatic compounds. Part 3 [1–3]

Abstract

A study was made of the use of calcium oxide as a catalyst at a temperature of 400–700° for the dehy‐drocyclization of four primary arylamines: 2‐aminobiphenyl, 1‐aminotriphenylene (5c), 2‐phenoxyaniline, and N‐(2‐aminophenyl)pyrrole. Maximal yields of cyclized products isolated were 53% (carbazole), 52% (4H‐naphtho[1,4‐def]carbazole), 18% (phenoxazine), and 0%, respectively. Comparison is made with reported cyclizations of the corresponding nitro and azido starting materials. In one case, treatment of I‐nitrotriphenylene with triethyl phosphite produced mainly diethyl N‐(1‐triphenylenyl)phosphoramidate (51%). Mono‐ and hemihydrochlorides of 5c are described. A mechanism for the catalyzed dehydrocy‐clization is proposed.

Synthesis of Carbazole, Acridine, Phenazine, 4H‐Benzo[def]carbazole and Their Derivatives by Thermal Cyclization Reaction of Aromatic Amines.

“…Mechanisms of intramolecular cyclization are not clear enough at the present time. In this paper, we propose a lit-tle different mechanism from previous one [11]. Plausible reaction mechanisms of 3 are shown in Scheme 4 from substituent effects of amino, methoxyl and nitro groups on cyclization step.…”

Synthesis of carbazole, acridine, phenazine, 4H‐benzo[def]carbazole and their derivatives by thermal cyclization reaction of aromatic amines

“…In this paper, we propose a little different mechanism from previous one [11]. Plausible reaction mechanisms of 3 are shown in Scheme 4 from substituent effects of amino, methoxyl and nitro groups on cyclization step.…”

“…In the previous paper [11], we reported synthesis of nitrogen-containing heterocycles such as carbazole 4 (53%), 4H-naphtho[1,4-def]carbazole (52%) and phenoxazine (18%) by passing aromatic amines dissolved in benzene over calcium oxide at 400-700°C. We modified the synthetic method of nitrogen-containing heterocycles without solvent and applied to several aromatic amines.…”