Organomagnesium reagents transmetalation

Transmetalation of Funct/oncrf/zect Organof/ihidm and Organomagnesium Reagents 47... 

Although lithiated 1,2,3,4-tetrahydroisoquinoline reacts with aldehydes with little diastereoselectivity, the presence of MgBr2 dramatically enhances the selectivity. /-Isomers are obtained from 2-pivaloyl-1,2,3,4-tetrahydroisoquinoline in > % de, and a u-isomer predominantly from a formamidine. In Ae latter case, an organomagnesium reagent (3) formed by transmetalation was shown to be the reactive intermediate (Scheme 15). ... 

The catalytic cycle involves the oxidative addition of aryl halide to Ni(0) precursor, the transmetalation of organomagnesium reagent to the resulting aryl(halogeno)nickel complex giving an aryl(alkyl)nickel(II) intermediate, and... 

Scheme 4.8 Preparation of sait-free diaikyizinc reagents from organomagnesium reagents by transmetallation with zinc salts [58, 59).

Transmetallation is widely used for the synthesis of organonickel complexes, especially those containing two Ni-C bonds. Probably because of their ready availability, organomagnesium reagents are the most commonly used by far. In addition, they often allow the introduction of one organic group in a selective manner. Recent examples of selective monoalkylation reaetions are shown in Equation and Seheme 4. The sterically crowded derivative 38 reversibly... 

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