Nickel catalysis arylation

Fig. 12. Comparison of the Copper and Nickel catalysis on the arylation of alcohols...

Several reports have been made of a successful catalyzed addition/ substitution reaction resulting in direct attachment of phosphorus to aromatic rings. The preparation of mixed triarylphosphines has been accomplished by the reaction of tin- or silicon-substituted diphe-nylphosphines with aryl halides catalyzed by palladium reagents.74 A similar transformation has also been reported using nickel catalysis.75 The addition/substitution of diphenylphosphine to triflate functionalized phenolic linkages has been of use for the preparation of substances as analogues of tyrosine-related amino acid derivatives, accomplished with catalysis by palladium acetate (Equation 4.29).76... 

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). 

Aryl cyanides add to norbornene and norbornadiene under nickel catalysis to give (2/U,35 )-3-aryl-2-cyanobicyclo[2.2.11heptanes and (2/U,3.S )-3-aryl-2-cyanobicy-clo[2.2.1]hept-5-enes in good yields with a broad substrate scope. On the other hand, the reaction of an aryl cyanide with triethoxy(vinyl)silane gives a Heck-type arylation product, suggesting the arylnickelation pathway in the catalytic cycle.68... 

Multiple-component difunctionalization reactions of a,/ -unsaturated carbonyl systems have been achieved by catalytic conjugate addition/aldol sequences. As Scheme 8.13 illustrates, an efficient method reported by Montgomery [46] allows regioselective addition of an aryl iodide to the /i-position of an unsaturated ester under nickel catalysis and subsequent trapping with an aldehyde to give / -hydroxyesters (e.g. 33). Significantly, premature termination of the sequence by the /Miydride elimination process that is usually observed in Pd-catalyzed Heck reactions does not occur here. 

Nickel catalysis in the electrosynthesis of aryl- and heteroarylzinc reagents, and in the electrochemical Reformatsky and allylation reactions using alkyl chlorides... 

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. 

An application of the nickel catalysis is shown here in the formation of 2,7-disubstituted derivatives of naphthalene, which are less common in the library of commercial fine chemicals. For these reasons, the submitters developed some synthetic routes to 2,7-bis(diethylcarbamoyloxy)naphthalene, 2,7-dimethylnaphthalene4 and 2,7bis(bromomethyl)naphthalene that will facilitate access to a large family of 2,7-disubstituted naphthalenes.5 The low cost of N,N-diethylcarbamoyl chloride, relative to triflic anhydride (for making aryl triflates), allows... 

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. 

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]. 

Nickel catalysis has also been used in the formation of biaryls, such as (51), by substitution of the methoxy group in 1-methoxynaphthalene by tolylmagnesium bromide. It is also reported that the reaction of aryl or heteroaryl tosylates with phenylmag-nesium bromide to give biaryl derivatives is catalysed by palladium complexed with heteroatom-substituted secondary phosphine oxide ligands. 

Under nickel catalysis, it was foimd that both azoles (Figure 13.13) [36] and tertiary ammonium salts (Figure 13.14) [37] can serve as effective coupling partners. Carbohydrate-based azoles, as well as aryl-azole substrates, were effective coupling partners. The use of ammonium salts was restricted to aromatic systems however, the use of a common structural motif is a significant improvement to the coupling methodology. 

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