Palladium‐Catalyzed para‐C−H Arylation of Anilines with Aromatic Halides.

Controlling regioselectivity in C−H functionalizations is a key challenge in chemical method development. In arenes, functionalizations are most difficult to direct towards the C−H group furthest away from a substituent, in its para position. We herein demonstrate how the para‐C−H arylation of anilines with non‐activated aryl halides, elusive to date, is achieved by a base‐assisted "metalla‐tautomerism" approach. A proton is abstracted from the aniline substrate and replaced by an arylpalladium species, generated from the aryl halide coupling partner. In this step, the palladium is directed away from the N‐ to the tautomeric para‐C−H position by a large phosphine ligand combined with a triphenylmethyl shielding group. The triphenylmethyl group is easily installed and removed, and can be recycled. [ABSTRACT FROM AUTHOR]