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 twofold arylation with diverse aryl iodides through cleaving unstrained aryl–aryl bonds of common 2,2′-biphenols. The reaction is catalysed by a rhodium complex and promoted by a removable phosphinite directing group and an organic reductant such as tetrakis(dimethylamino)ethylene. 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 phenylene units.