Suzuki cross-coupling aryl halides

Today, the Suzuki cross coupling of aryl halides and arylboronic acids is also carried out in aqueous-biphasic operation starting from chlorinated derivatives instead of their more costly bromo or iodo equivalents (Equation 5.6, [39]). 

Leadbeater and Griffiths developed palladium catalysts for the Suzuki cross-coupling of aryl halides bearing two ortho substituents with phenylboronic acid, and used them in the synthesis of sterically hindered biaryls [83]. 

Most recently, Fu and co-workers [126] have reported that the use of Pd2(dba)3/PtBu3 as a catalyst for a wide range of aryl and vinyl halides, including chlorides, facilitates their Suzuki cross-coupling with arylboronic acids, giving the coupled products in very good yield, typi-... 

Littke, A. F., Dai, C., Fu, G. C. Versatile Catalysts for the Suzuki Cross-Coupling of Arylboronic Acids with Aryl and Vinyl Halides and Triflates under Mild Conditions. J. Am. Chem. Soc. 2000,122, 4020-4028. 

More recently, a protocol was elucidated by Malezcka and Smith to produce aryl borate esters directly without first producing aryl halides.144 The reaction involves an Ir-catalyzed C-H activation (Section 7-2-1) to yield the aryl borate, which can then be used directly in Suzuki cross-coupling (equation 12.71). This new development adds another green aspect to Suzuki cross-coupling, which is already a relatively green synthesis tool. 

Palladium acetate is better than PdCl2(dppf) in terms of cost and catalyst removal and effectively catalyzes the cross-coupling of a wide variety of aryl halides with bis(pinaco-lato)diboron to form the corresponding boronates. These boronates can be conveniently isolated or used in situ for Suzuki cross-coupling reactions with aryl halides to provide biaryls [189b]. 

The cross-coupling reactions of various aryl halides and triflates with vinyl- or arylboronic acids and esters (Suzuki cross-coupling reaction) was also carried out in water in the presence of tetrabutylammonium bromide and a base such as Na2C03, using a phosphine-free palladium catalyst to give biaryl derivatives [Eq. 18)1 [108,109]. More recently, Casalnuovo [101] and Gen t [102,110] have performed this reaction using water-soluble palladium catalysts PdCla (tppms)2 and Pd(OAc)2/tppts in water/acetonitrile. 

Diarylimidazoles were prepared by Suzuki cross-coupling reactions of imidazole halides with arylboronic acids <05H(65)1975>. Suzuki cross-coupling reactions of 6-bromoimidazo[l,2-a]pyridines have been developed <05H(65)2979>. Cul-catalyzed iV-arylation of imidazoles and benzimidazoles with aryl bromides was achieved in a near-homogeneous system that utilized tetraethylammonium carbonate as base, 8-hydroxyquinoline as ligand and water as cosolvent <05JOC10135>. 

The reaction is not restricted to forming biaryls. Aryl boronic acids can also react with vinyl halides and vinyl triflates in the presence of palladium (0). Thallium (I) ethoxide is known to promote Suzuki cross coupling reactions for vinyl or arylboronic acids with vinyl and aryl halide partners. 3 synthetic example is... 

---