Transition-Metal-Free Synthesis of Carbazoles by Photostimulated Reactions of 2′-Halo[1,1′-biphenyI]-2-amines

An efficient and simple protocol for the preparation of a series of 9H-carbazoles by photostimulated S(RN)1 substitution reactions is presented. Substituted 9H-carbazoles were synthesized in low to excellent yields (up to 96%) through an intramolecular C-N bond formation of 2'-halo[1,1'-biphenyl]-2-amines by the photoinitiated S(RN)1 mechanism under mild and transition-metal-free conditions. The biphenylamines used as substrates were obtained with isolated yields ranging from 21% to 84% by two approaches: (A) the cross-coupling SuzukiMiyaura reaction and (B) the radical arylation of anilines. Some key aspects of the proposed mechanism were evaluated at the B3LYP/6-311+G* level.