Thermal reactions of N ‐alkyl‐2‐benzylaniline and N ‐alkyl‐ N ′‐phenyl‐ o ‐phenylenediamine: An unusual route to 2‐phenylindole and 2‐phenylbenzimidazole

Thermal cyclization reactions of N ‐alkyl‐2‐benzylaniline 1a‐d and N ‐alkyl‐ N ′‐phenyl‐ o ‐phenylenediamine 2a‐b were carried out expecting to get seven‐membered heterocyclic compounds. However, the results show that aside from the formation of the normally expected six‐membered ring products of acridine 5 , anthracene 6 , and phenazine 8 , thermal cyclization of N ‐alkyl‐2‐benzylaniline and N ‐alkyl‐ N ′‐phenyl‐ o ‐phenylenediamine also resulted to the unexpected formation of 2‐phenylindole 3 and 2,3‐diphenylindole 4 , and 2‐phenylbenzimidazole 7 , respectively.