Recent advances in aryl–aryl bond formation by direct arylation

The abundance of the biaryl structural motif in natural products, in biologically active molecules and in materials chemistry has positioned aryl–aryl (Ar–Ar) bond formation high on the agenda of synthetic chemists. For decades well-known reactions such as the Mizoroki–Heck and Suzuki–Miyaura have been the methods of choice to furnish biaryls. More recently, however, alternative methods, most notably direct arylation via C–H activation, have become the focus of many research groups. Compared to traditional methods, direct arylation affords Ar–Ar compounds in fewer steps by removing the need for prefunctionalisation. Furthermore, given that either one or two hydrogens are targeted, less waste and good atom economy are features of this methodology. This critical review covers, in the main part, reports from January 1, 2006, to October 22, 2008 (117 references).