Nickel hydrozincation

A more convenient, but less general, synthesis of diorganozincs from olefins is the nickel-catalyzed hydrozincation, shown in Scheme 6. The yields (40-63%) are independent of the amount of diethylzinc added, but dependent on the nature of the olefin. For allylic and homoallylic alcohols and amines, yields as high as 85-95% are possible.32,33... 

Diorganozincs can also be prepared by a nickel-catalyzed hydrozincation. The reaction of Et2Zn with Ni(acac)2 may produce a nickel hydride that adds to an alkene leading. 

Diorganozincs can also be prepared by a nickel-catalyzed hydrozincation. The reaction of Et2Zn with Ni(acac)2 may produce a nickel hydride that adds to an alkene leading after transmetallation with Et2Zn to a diakylzinc (Scheme 9). This reaction proceeds in the absence of solvent and at temperatures of 50-60 °C. A number of functionalized olefins like allylic alcohols or amines can be directly used. This method is especially well suited for the preparation of functionalized diorganozincs for the asymmetric addition to aldehydes (Equation (45)).108,50... 

The nickel-catalyzed hydrozincation of alkenes has been developed as a useful entry to functionalized organozincs (Scheme 3-85). Simple terminal olefins, when treated with EtaZn and catalytic quantities of Ni(acac)2 and cyclooctadiene, are efficiently converted into the corresponding dialkylzinc reagents from hydrozincation of the alkene. A wide variety of copper-catalyzed alkylations are accessible... 

The nickel-catalyzed hydrozincation of alkenes provides a novel method for the preparation of functionalized organozincs such as (97) (Scheme 77).H74.i75] resulting ftmction-alized organozincs may be transformed into cuprate reagents and then alkylated with a variety of electrophiles. A hydronickelation step is likely involved in the reaction pathway. 

Nickel A three-component hydrozincation of alkynes R C=CR with Et2Zn (3 equiv.), carried out under the atmosphere of CO2 (at normal pressure), has been shown to form ( )-conflgured hydrocarboxylation products R CH=C(R )C02H in the presence of (COD)2Ni as a catalyst (l-3mol%) and CsF (1 equiv.) in MeCN at 60 °C over 1.5h.i ... 

Vettel, S., Vaupel, A. and Knochel, P. 1995. A new preparation of diorganozincs from olefins via a nickel catalyzed hydrozincation. Tetrahedron Lett. 36 1023-1026. 

Scheme 4.21 Preparation of dialkylzinc reagents by nickel-catalyzed hydrozincation of alkenes [89, 94].

The nickel-catalyzed hydrozincation or carbozincation of double or triple bonds are worthy of note. Thus, treatment of an alkene with diethylzinc in the presence of a catalytic amount of Ni(acac)2 and COD affords the corresponding organozinc reagent. Since diethylzinc will react with aliphatic bromide or iodide, such zinc-... 

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