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

A variety of nitrogen-containing heterocycles were synthesized by passing vapors of aromatic amines over calcium oxide at 450-650 degreesC under nitrogen carrier gas. Reaction of 2-aminobiphenyl 3a at 560 degreesC gave carbazole 4 in 80% yield. Reaction of 2,2'-diaminobiphenyl 3b afforded a mixture of carbazole 4 and 4-aminocarbozole 6b. In the case of 2-amino-2'-nitrobiphenyl 3c, benzo[c]cinnoline 7 was obtained along with carbazole 4. Reaction of 2-amino-2'-methoxybiphenyl 3d gave four products of carbazole 4, 4-hydroxycarbazole 6e, phenanthridine 8 and dibenzofuran 9. Reaction of 2-aminodiphenylmethane 5a afforded acridine 10. In the case of 2-aminobenzophenone 5b, acridone 11 was obtained as a major product. Reaction of 2-aminobenzhydrol 5c gave acridine 10. When 2-aminodiphenylamine 5d was reacted, phenazine 12 was obtained in good yield. In contrast, reaction of 2-aminodiphenyl ether 5e produced only 2-hydroxydiphenylamine 13. Reaction of 4-aminophenanthrene 14 produced 4H-benzo[def]carbazole 15 in 61% yield.