Ligand-Enabled ortho-Arylation of (hetero)Aromatic Acids with 2,6-Disubstituted Aryl Halides

Directed C-H arylations have proven to be some of the most advantageous strategies for the synthesis of biaryls. However, their sensitivity toward steric hindrance is a key limitation. Couplings of 2,6-disubstituted aryl halides with arenes have so far been elusive. This weakness is overcome by a ruthenium 3,4,7,8-tetramethyl-1,10-phenanthroline catalyst. It allows the selective ortho-C-H arylation of widely available (hetero)aromatic acids with bulky aryl halides in up to 95% isolated yield. 46 examples of tri-substituted (hetero)biaryls, all outside the scope of established catalyst systems, demonstrate the efficiency of the protocol. Computational and experimental studies illustrate how this unique combination of carboxylate directing group and chelating N-ligand facilitates the selectivity determining C-H activation step. The preference for oxidative addition of the aryl halide over competing benzoic acid coordination is decisive to suppress unwanted dehydrogenative homocoupling.

Automated summary

Directed C-H arylations are widely used strategies for the synthesis of biaryls. However, their sensitivity to steric hindrance is a limitation. In this study, a ruthenium catalyst is used to overcome this limitation and achieve high yields of ortho-C-H arylation. The combination of a carboxylate directing group and chelating N-ligand is found to be crucial for the selectivity of the reaction.