Alkyl nickel-catalyzed arylations

Nickel-Catalyzed Arylations of Alkyl (Pseudo)Halides... 

Nickel catalysts show a high reactivity and a broad substrate scope in the arylation of alkyl halides. While only aUcyl haUdes without P-hydrogens were used in the early examples of nickel-catalyzed arylations of alkyl halides, highly efficient arylations at the a-position of a gem-dimethyl-substituted quaternary center highlighted its synthetic potentials (Equation 5.14) [16, 17]. 

Recently, bipyridines and amino alcohols, which were rather unique ligands for conventional nickel-catalyzed cross-coupling reactions, have been shown to be eflective for nickel-catalyzed arylations of secondary alkyl halides. Fu reported that a combination of [Ni(cod)2] and bathophenanthroline 13 catalyzed the cross-... 

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). 

Fig. 2 Nickel-catalyzed alkyl-alkyl and alkyl-aryl Suzuki-Miyaura coupling reactions...

Fig. 21 Nickel-catalyzed reductive cross-coupling of aryl and alkyl halides...

Finally, the mechanism in Scheme 3 bears a resemblance to that presented above for the nickel-catalyzed reaction of methylmagnesium bromide and aryl bromides. However, there are outstanding differences between iron and nickel in their abilities to effect cross coupling reactions. Iron is a catalyst which is effective at lower temperatures and concentrations than used with nickel. Even more importantly, cross coupling can be effected completely stereospecifically with an iron catalyst and no alkyl isomerization of the Grignard component has been observed, in contrast to the nickel-catalyzed reactions. 

A simple way to avoid toxic and intractable triorganotin waste is to use monoorganotin reagents that are much less toxic and less lipophilic. Unactivated secondary alkyl halides can be coupled with aryl-trichlorotin in a nickel-catalyzed Stille cross-coupling reaction" (e.g. Scheme 5.8.15). 

Alkylation and arylation by nickel-catalyzed reactions with organomagnesium reagents... 

Other coupling partners to organozinc reagents include heterocyles such as 2-methylthiobenzothiazole, alkenyl aryl iodonium triflates (alkenyl group transfer for synthesis of trisubstituted alkenes), and aryl heteroaryl ethers. " Improved nickel-catalyzed cross-coupling conditions between oz-rto-substituted aryl iodides-nonaflates and alkyl-zinc iodides in. solution and in the solid phase have been defined. ... 

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