Synthesis of benzidine derivatives via FeCl3·6H2O-promoted oxidative coupling of anilines.

Under open-flask conditions in the presence of commercially available FeCl3·6H2O, N,N-disubstituted anilines can be converted into diversely functionalized benzidines with yields of up to 99%. Oxidative coupling was extended to N-monosubstituted anilines, and the method was applied to the efficient preparation of 6,6'-biquinoline. Mechanistic investigations have also been performed to explain the observed reactivities.