Transition Metal-Catalyzed Couplings of Nonactivated Aryl Compounds

4 Transition Metal-Catalyzed Couplings of Nonactivated Aryl Compounds 

Over the last few years, functionalization by means of C—H activation has gained considerable importance for several reasons, including atom economy, the drastic decrease of undesired by-products, and reduced costs for the preparation of substrates, which are often available in fewer steps. In this respect, recent efforts were devoted to the elaboration of efficient protocols for the direct transition metal-catalyzed aryl-aryl bond formation of nonactivated aromatic snbstrates [63, 68, 69]. 

More commonly, the transition metal-catalyzed coupling of aryl halides with nonfunctionalized aromatic substrates has been used for the preparation of unsymmetrical biaryl systems. Different strategies have been developed over the last few years. One very elegant approach utilizes directing groups on aromatic substrates. The lone pair of the requisite heteroatom coordinates to the transition metal and promotes the arylation reaction via intermediary formation of a five-or six-membered metallacycle. 

SCHEME 12.34 Eunctional group tolerance of the Suzuki reaction. 

FIGURE 12.3 Novel boron derivatives, leaving groups, and ligands for the Suzuki coupling. 

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