Cross-coupling reactions arylzinc-aryl halides

The procedure described above is based on a paper reporting the Ni- or Pd-catalyzed reaction of arylzinc derivatives with aryl halides. The Ni- or Pd-catalyzed cross coupling reaction represents one of the most general and satisfactory routes to unsymmetrica1 biaryls. 

Nickel (0) reagents have been employed in the symmetrical coupling of aryl halides in sterically unencumbered cases. An efficient cross coupling reaction between an arylzinc halide and an ortho-iodoaryllmlne under mild conditions mediated by N1(0) has been reported. Thallium(III)... 

The cross-coupling of organozinc compounds has been accomplished using a number of metal enolate complexes, namely Rh(acac)(H2C=CH2)2 (6) , Co(acac)3 (30) °, Ni(acac)2 (47) , Li(acac) (107) and Cr(acac)3 (108) . For instance, complex 47 proved to be an extremely effective catalyst system for the Negishi cross-coupling of arylzinc halides (109) with aryl (110), heteroaryl and alkenyl halides, triflates and nonaflates to give the corresponding biaryl compounds (111) (equation 30). The solvent played an important role in these reactions and optimal conditions were found with 8 1 mixtures of THF and A-ethylpyrrolidinone (nep). Only 0.05 mol% of the nickel complex... 

Knochel reported that a combination of diethyl phosphite-DMAP and Ni(II) salts formed a very effective catalytic system for the cross-coupling reactions of arylzinc halides with aryl, heteroaryl, alkenyl bromides,... 

The Reformatsky reagents, i.e. zinc enolates of esters, undergo Ni catalysed cross-coupling with aryl halides.53 The Ni catalysed reaction of arylzincs with a-bromoacetates also permits a-arylation of esters54 (Scheme 11.13). However, a-alkenylation of enolates of ketones, aldehydes, and esters has been less satisfactory. Its further development is clearly desirable. Alternatively, a-alkenylation of a-iodoenones in conjunction with conjugate reduction discussed earlier should be considered. 

Radical addition/cross-coupling products 61 were obtained in 60-91% yield when Ni(dppf)Cl2 was applied as a catalyst in reactions of alkyl halides 60 with 2,3-disubstituted dienes 59 and aryl Grignard or arylzinc reagents (Fig. 12). Competition experiments of n-, sec-, and ferf-butyl bromide with 2,3-dimethylbutadiene... 

The use of the well-defined PEPPSI-IPr precatalyst led to a significant improvement with respect to the rate and the substrate scope of the Negishi alkyl-alkyl coupling reactions (Scheme 3.62). This precatalyst can also be used to promote the cross-couphng of alkyl or aryl halides and sulfonates with arylzinc chloride reagents at room temperature by judicious choice of the solvent and additive (LiCl or LiBr) [236]. 

---