Alkenylzinc chlorides

E)-(2-Bromoethenyl)dibromoborane, BrCH==CHBBr2, can be used in place of 1 to couple alkylzinc chlorides with an alkyl chloride to form a monoene, but this reagent is unsatisfactory for coupling of alkenylzinc chlorides.1... 

Hydrozirconation of various alkenylboranes [118-121] and alkenylzinc halides [34] with 1 provides the corresponding 1,1-bimetalloalkanes, which can be selectively converted to functionalized organic compounds [122-125]. Interestingly, alkenylzinc halides (RCH=CHZnX) show remarkable chemoselectivity, and functional groups such as chloride, cyanide, or ester functionality are tolerated [126]. 

Recently, Oshima has reported a cobalt-catalyzed allylzincation of internal alkyne derivatives (Scheme 10). Optimization of the reaction leads to utilization of cobalt(ll) chloride in THF at room temperature. No traces of regio- and stereoisomers are obtained. The resulting alkenylzinc species 34 can be trapped with a large number of electrophiles in order to generate stereoselectively the tri- and tetrasubstituted alkenes 35-37. 

Remarkably, the hydrozirconation can be applied to functionalized alkenylzinc reagents bearing an ester, chloride, or cyano functionality (Scheme 7.37) [230], The functionalized bimetallic species 129c—e gave significantly lower yields (55—64%) but excellent stereoselectivities (>94% ( ) Scheme 7.39). Although the (E)/(Z) ratio was always reproducible,... 

Acylation of organozinc reagents. Reaction of acyl chlorides with organozinc compounds catalyzed by palladium-phosphine complexes provides a general synthesis of ketones. The organozincs are readily available by treatment of the corresponding organo-lithium with ZnCh. Alkenylzinc compounds and a,p-unsaturated acyl chlorides react with retention of the stereochemistry. Isolated yields of ketones are 55-90%. 

Dienes.1 (E)-l-Alkenylalanes, readily obtained by hydroalumination of 1-al-kynes,2 couple with vinyl iodides in the presence of this Pd(0) catalyst and zinc chloride to give 1,3-dienes with retention of the configuration. Alkenylzinc derivatives may be the actual reactants. Nickel catalysts are less stereoselective than palladium-phosphine catalysts. 

Addition of Cp2Zr(H)Cl to an alkenylzinc hahde affords relatively unstable 1,1-bimetallics of Zn and Zr. Addition of an aldehyde or a ketone is a general way to synthesize ( )-alkenes. Remarkably, the hydrozirconation can be applied to functionahzed alkenylzinc reagents bearing an ester, chloride or cyano functionahty (equation 43). ... 

Coupling reactions. Cobalt(II) bromide catalyzes the coupling of diorganozincs RjZn, allylic chlorides and phosphates without disturbing the configuration of the double bond." Other couplings useful for skeletal construction feature alkenylzinc compounds with... 

Coupling of organozincs with aryl halides. The method is very useful for the synthesis of biaryls,including heterobiaryls.Vinylic, " aliphatic zinc reagents, and even Zn(CN>2 are reactive toward ArX in the presence of (Ph3P)4Pd. Perfluoro-alkenylzinc bromides and cyclopropenylzinc chlorides also couple efficiently with iodoarenes. 

Scheme 4.51 Pd-catalyzed cross-coupling of alkenylzinc halides with alkyl chlorides [189].

The range of nucleophiles can be extended to alkenylzinc reagents. These species are subjected to alkyl chlorides, bromides, or iodides in an iron-catalyzed Negishi coupling to efficiently form olefins (Scheme 4-235). Iron(III) chloride fiinctions as a precatalyst in the presence of TMEDA. ... 

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