Polyaniline‐Induced Arylation with Arenediazonium Salts Derived from Anilines

A catalytic amount of a reduced form of polyaniline (a redox‐active π‐conjugated polymer) was found to induce C−H direct arylation of (hetero)arenes with arenediazonium salts prepared from anilines with methanesulfonic acid (MeSO 3 H) and tert ‐butyl nitrite ( t BuONO). The difficult part of this method is the coexistence of an oxidant and a reductant in this sequential diazotization and arylation system; diazotization requires weak oxidants such as alkyl nitrites, whereas the arylation is induced by a reductant. This was achieved by the careful control of the amount of t BuONO (1.0 equivalent) for the diazotization step, and sequential arylation using 5 mol % of the polyaniline. The reaction took place under mild conditions without any metals or strong bases at room temperature, and the amino group is a formal leaving group. The scope of the substrates demonstrates the versatility in the combination of anilines with a variety of functional groups and several (hetero)arenes. Two‐directional arylation for the synthesis of an unsymmetrical 1,4‐diarylated (furyl and pyrrolyl groups) benzene was achieved, using mono‐Boc‐protected 1,4‐phenylenediamine as a substrate. This shows potential for the synthesis of more complicated oligoarene compounds.