Hydrozincation with

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. 

Hydrozincation of terminal alkene with Et2Zn, catalysed by Ni(acac)2, yields the dialkylzinc 525, which reacts with the nucleophile 526 via transmetallation involving Cu salt to give 527 [199]. In this reaction, the Ni hydride is generated by / -elimination of EtNi(acac), and the hydronickellation product 524 is formed by alkene insertion to the hydride H—Ni(acac). Then transmetallation of 524 with Et2Zn affords 525. 

The direct hydrozincation of olefins14 is possible using Et2Zn in the presence of catalytic amount of Ni(acac)2 and 1,5-cyclooctadiene (COD). The resulting diorganozincs can be used for asymmetric additions to aldehydes. The best hydrozincation reactions are obtained with allylic alcohols or amines. In these cases the raction is driven to completion by the formation of a zinc-heterocycle of type 7 (Scheme 5.10). 

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... 

HydroZinc A biological process for leaching zinc from heaps of zinc sulfide ore. Naturally occurring bacteria attack the ore, and the leachate is then neutralized and extracted with a solvent. The metal is produced from this liquor by electrowinning. The process was developed by Teck Cominco in British Columbia and piloted between 2000 and 2002. 

Hydrotitanation of 1-silyl- and I-stannyl-1-alkynes leads to P-silyl (or p-stannyOalkenyltitanates, thus showing opposite regioselectivity to other related processes (hydroboration, hydroalumination, hydromagnesiation, hydrotitanation, hydrozincation, hydrozirconation).Well-defined alkenes are obtained on further reaction of the alkenylti-tanates, for example, with allylic carbonates an 8 2 displacement occurs to afford 1,4-di-... 

Organocopper reagents prepared from the more readily available organozincs have found much use in the synthesis of highly functionalized molecules. For example, Ni-catalyzed hydrozincation of allylic alcohols initiates the preparation of a-(4-hydroxyalkyl)acrylates when the cuprate intermediates are used in the coupling with the a-bromomethylacrylic esters." ... 

This method can be exploited as part of a one-pot hydroalkylation of an internal alkyne. Thus, titanium-catalyzed syn hydrozincation [24], followed by Negishi cross-coupling with an alkyl halide, stereospecifically generates a trisubstituted olefin (Eq. 8). 

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 ... 

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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