Arylboronic homo-coupling

Biaryls. Various arylmetals, arylboronic acids, and arylfluorosilanes undergo Pd(II)-catalyzed homo-coupling using 2,3-dibromoalkanoic esters as oxidants. 

Table 7. Synthesis of symmetrical biaryls via in situ generation of arylboronic acids from aryl iodides and bromides followed by the homo-coupling reaction with silver(I) nitrate [19,20]...

However, practical synthetic method for performing the homo-coupling of arylboronic acids to the respective symmetrical biaryls is accomplished with copperfll) nitrate as an ultimate oxidant in good to high yields, Table 8. 

Table 8. Palladium-catalysed homo-coupling reaction of arylboronic acids to symmetrical biaryls in the presence of copper(II) nitrate as an oxidant...

Homo-coupling of arylboronic acids Preparation of 2,2 -binaphthyl (166) 122]... 

Uemura has shown that aryl chlorides which are T -bound to Cr(CO)3 are remarkably reactive coupling partners in Suzuki reactions [23, 24]. Even in the presence of the electron-donating, deactivating ortho-methoxy substituent, the aryl chloride couples with an arylboronic acid (Equation 2.13). Furthermore, no homo-coupled 4 -bromobiphenylboronic acid is observed, establishing that highly selective activation of a C—Cl bond is occurring in the presence of a typically more reactive C—Br bond. 

Mitsudo K, Shiraga T, Tanaka H (2008) Electrooxidative homo coupling of arylboronic acids catalyzed by electrogenerated cationic palladium catalysts. Tetrahedron Lett 49 6593-6595... 

A third potential side reaction is the homo-coupling of arylboronic acid to give the biaryl product (Section 5.9.3) [23a]. This has also been reported recently by Demir et al. [53]. DMF is the preferred solvent to generate more homocoupled biaryl products. 

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