Split cross-coupling via Rh-catalysed activation of unstrained aryl-aryl bonds.

Constructive functionalization of unstrained aryl-aryl bonds has been a fundamental challenge in organic synthesis due to the inertness of these bonds. Here we report a split cross-coupling strategy that allows two-fold arylation with diverse aryl iodides through cleaving unstrained aryl-aryl bonds of common 2,2'-biphenols. The reaction is catalyzed by a rhodium complex and promoted by a removable phosphinite directing group and an organic reductant. The combined experimental and computational mechanistic studies reveal a turnover-limiting reductive elimination step that can be accelerated by a Lewis acid co-catalyst. The utility of this coupling method has been illustrated in the modular and simplified syntheses of unsymmetrical 2,6-diarylated phenols and skeletal insertion of phenyl units.