Grignard reagents, reactions nickel-catalysed

The nickel-catalysed reaction of aryl, allyl or vinyl sulfides with Grignard reagents has been found to be an effective way for the conversion of carbon-sulfur bonds into carbon-carbon bonds [318]. However, simple aliphatic substrates are inert. 

Reactions of organomagnesium compounds with dialkyl sulfates or alkyl sulfonates often give satisfactory yields of the products of displacement of sulfate or sulfonate. Side-reactions have been observed, but they can often be avoided for example, an excess of the sulfate or sulfonate should be used with Grignard reagents, as some is consumed by nucleophilic attack by halide ion [A]. The dialkyl sulfates are reactive, but hazardous. Toluenesulfonates (tosylates) are less reactive, but their reactions are catalysed by copper complexes the reactions of trifluoromethanesulfonates (triflates) are catalysed by nickel complexes. Reactions of Grignard reagents with secondary tosylates appear to follow an Sn2 mechanism, with inversion of configuration [43],... 

CROSS-COUPLING REACTION OF ALKYL HALIDES WITH GRIGNARD REAGENTS IN THE PRESENCE OF 1,3-BUTADIENE CATALYSED BY NICKEL, PALLADIUM, OR COPPER... 

Ni and Pd catalysts were found to be most useful for this purpose [35]. Palladium catalysed reactions show better chemoselectivity, but are restricted to activated aryl bromides while nickel-catalysed processes are more tolerant to steric hindrance of aromatic substituents [36]. These reactions are the best alternative to Ni(0) catalysed high temperature coupling of aryl halides [37]. With stericaly hindered aryl halides generation of a Grignard reagent is recommended. Preferably the component with an ortho substituents should be converted the Grignard compound[38]. 

Fu et al. showed that a combination of NiCla and bis(oxazoline) 11 or 17 catalyses asymmetric Kumada coupling of racemic a-bromoketones with aryl Grignard reagents, giving a-arylketones in good yields and enantiomeric excess (Scheme 14.8). The reactions proceeded at low temperature, which enabled the asymmetric synthesis of racemisation-prone a-arylketones. The Pincer-nickel complex [(N2N)Ni-Cl] (18) catalyses Kumada reaction of primary allqrl bromides/iodides or secondary all l iodides with alkyl, (hetero)aryl or all nyl Grignard reagents (Scheme 14.9). The reactions... 

Grignard reagents tBuMgBr or Bu2Mg were also used as the hydride source for nickel-catalysed hydrodecyanation reactions of aryl and allyl... 

The Grignard reagents are far more applicable counterparts in the nickel- and palladium-catalysed Kharasch cross-coupling reactions with aryl halides (1, Br, Cl), as well as aryl triflatcs, to give biaryls in moderate to excellent yields [19]. In early... 

Table 2. Synthesis of biaryls via nickel-catalysed cross-coupling reaction of arylnitriles with aryl Grignard reagents [32]...

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