Cross-Coupling reactions, transition-metal-catalyzed Grignard reagents

Although cobalt catalysis is somewhat less developed compared to other transition metal catalysis for cross-coupUngs, but has shown rather unconventional, novel reactivity profiles [50]. For example, Oshima reported a cobalt-catalyzed tandem radical cyclization/cross-coupling reaction between an aryl Grignard reagent and an alkyl halide bearing an (o-alkenyl group (Equation 5.44) [51]. 

The transition metal catalyzed carbon-carbon bond formation between organomagnesium reagents and aryl (vinyl) halides has been one of the pioneering entries into cross-coupling chemistry. The reaction has been widely utilized since than in azine chemistry,22 with the limitation that the functional group tolerance of Grignard reagents is only moderate. Here only some of the more recent developments will be mentioned. 

For transition metal-catalyzed cross-coupling reactions of Grignard reagents, see the appropriate transition metnL... 

The effect of the ligand on the stereochemical course of a reaction catalyzed by a transition metal compound can be significant. For example, in the nickel-catalyzed cross-coupling reactions of alkyl Grignard reagents and aryl halides, the effect of changing the ligands on the metal is summarized in Fig. 13 (66, 67). 

Selective cross-coupling reactions between C(sp ) and C(5p ) centers had been one of the most difficult tasks in carbon-carbon bond synthesis until the early 1970s, when it was first reported that iron, nickel, palladium and copper - catalysts are extremely effective for cross-coupling of Grignard reagents with organic halides. Now, nearly 20 years later, transition metal catalyz cross-coupling has become the reaction of first choice for this purpose. 

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