Site-Selective N-Arylation of Carbazoles with Halogenated Fluorobenzenes

A method for the highly site-selective C–N bond-formation reaction of halogenated fluorobenzenes with carbazoles is described. The selectivity of iodine and fluorine atoms on the aromatic ring of fluorinated iodobenzenes was initially determined with a copper–N,N-diisopropylethylamine catalytic system. By changing the position of the iodine atom on the aromatic ring from the 3- or 4-position to the 2-position, the preferred coupling site was switched from the iodine atom to the fluorine atom. Steric hindrance of the fluorinated iodobenzenes is responsible for the selectivity switch. After elucidating the reaction mechanisms of these reaction processes, a metal-free method for the highly site-selective C–N bond-formation reaction of halogenated fluorobenzenes with carbazoles was revealed through C–F bond activation. The metal-free system is able to handle a range of halogenated groups. Thus, a broad range of chlorinated, brominated, and iodinated N-arylated carbazoles were generated, which are widely useful in organic chemistry.