Nickel catalysis coupling

Similarly, nickel catalysis permits the extension of cross coupling to vinyl phosphates, which are in some cases more readily obtained and handled than vinyl triflates.273... 

Nickel catalysis has been used in a sequential synthesis of terphenyls, starting with 2-, 3-, or 4-bromophenyl neopentanesulfonates. Conventional Pd-catalyzed Suzuki conditions were used for the first step involving coupling of the bromide and then nickel catalysis was utilized for coupling the sulfonate. 

Keywords Allylation Carbonyl compound Dienes Homoallylation Nickel catalysis Reductive coupling... 

Hocek and coworkers studied the regioselectivity of the cross-coupling reaction between methyhnagnesium bromide and various dichloropurines. With 2,6- and 2,8-dichloropurines, it is possible to obtain the monomethylated product with an excellent regioselectivity (Scheme 33). It is important to notice that such a regioselectivity is not observed under palladium or nickel catalysis. 

Recently, this reaction has been extensively studied since it is currently the only method to couple aryl Grignard reagents with secondary alkyl halides Indeed, secondary aUtyl halides do not react under palladium or nickel catalysis . On the other hand, let us recall that the coupling of secondary alkyl Grignard reagents with aryl halides leads to poor results (see above). 

Thienylmagnesium or zinc derivatives can be coupled with vinyl halides, bromo- or iodobenzene, or ethynyl bromide under Ni or Pd catalysis (Scheme 148) a thien-2-yl Grignard reagent was coupled twice to 3,6-dibromocar-bazole using nickel catalysis <1997CM1578>. The reaction can be extended to the synthesis of -styrylthiophene in this case the double-bond configuration is retained in the product. 

The BINAP ligand, 78, which is often used in asymmetric catalysis, possesses axial chirality in the binapthyl ring system as opposed to an asymmetrically substituted carbon atoms. They are made from chiral precursors using a nickel-catalysed coupling as the key step.23... 

A. Nickel Catalysis in the Cross Coupling of Aryl Halides with Alkylmetals. The Role of Arylalkylmckel(II) Species as Intermediated For the study of nickel catalysis in the formation of aralkanes, we employed the system consisting of aryl bromides and methyllithium or methylmagnesiiun bromide. 

Scheme 15.50. A solvent-free Sonogashira coupling employing nickel catalysis.

Kappe and Stadler have developed an MW procedure for rapid production of triaryl phosphines by coupling diphenylphospine with aryl halides and triflates [134]. Taking into account the importance of phosphine ligands in a variety of transition metal-catalyzed reactions, convenient procedures for their production is valuable. Both homogeneous Pd-Ni and heterogeneous Pd catalysts were explored and the more unusual substrate phenyl triflate could also be coupled swiftly by use of nickel catalysis (Scheme 15.68). Couplings with other aryl halides proceeded in 26-85% yield after 3-30 min microwave irradiation at 180-200 °C. 

Recently it has proved possible to cross-couple alkylzinc halides with primary alkyl haUdes. This can be achieved under nickel catalysis in the presence of tetra-butylanunonium iodide and4-lluorostyrene (1.141). As expected with this chemistry, the reaction tolerates a range of functional groups such as the presence of ketones and carboxyUc esters. 

Magnesium Reagents. Nickel catalysis is conunonly used for cross-coupling reactions involving organomagnesium reagents. Palladium catalysis is often less efficient but more selective. In 2,3-dibromothiophene selective reaction in the 2-position gives the monocoupled product 48 (Scheme 24). Selectivity is rationalized by activation of the 2-position by the annular heteroatom. Monosubstitution can also be effected in 2,5-dibromothiophene to yield the bithienyl 4,9... 

The tremendous popularity of palladium catalysis has overshadowed the utility of nickel catalysis in most processes involving the union of sp -sp and sp-sp carbon-carbon bonds. However, the development of nickel-catalyzed cross-couplings emerged as useful in couplings of aryl chloride substrates. The high reactivity of nickel catalysts toward aryl chlorides, coupled with the well-defined mechanistic pathways of aryl chlorides compared with the corresponding aryl iodides and bromides, renders the aryl chloride-based processes especially useful. " ... 

In 1998, Knochel reported that, in the presence of 4-trifluoromethylstyrene, [Ni(acac)2] efficiently catalyzed cross-couplings between polyfunctional arylzinc derivatives and alkyl halides possessing P-hydrogens (Equation 5.15). While the alkyl halides were limited to primary alkyl iodides, the scope of nickel catalysis was significantly expanded. The role of the electron-deficient olefin, 4-trifluoromethylstyrene, was proposed to accelerate the reductive elimination step by decreasing the electron density at the nickel center of an (alkyl) (aryl)nickel intermediate [18]. 

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