Electrophilic allyl derivatives transmetallation

On the other hand, transmetalation to copper and further reactions with electrophiles occur preferentially at the phenyl-bearing carbon of unsymmet-rically substituted zirconacyclopentadiene derivative 35 (Scheme 17). The presence of lithium salts should be avoided to prevent the double allylation reaction of the zirconacyclopentadiene derivative [46]. 

The overall reaction makes it possible to perform intramolecular caibozincations [65-71] via a radical cyclization. This useful preparation of cyclopentylmethylzinc derivatives proceeds with excellent stereoselectivity and allows preparation of quaternary centers. After cyclization, the zinc organometallic can be transmetallated with CuCN-2LiCl and made to react with a broad range of electrophiles such as acid chlorides, allylic and alkynyl halides, ethyl propiolate, 3-iodo-2-cyclohexen-l-one, and nitroolefins such as nitrostyrene, leading to products of type 40 (see Section 9.6.9 Scheme 9-34) [65,70]. 

Oxidative Heck reactions via Pd(II) C—H functionalization of terminal alkenes with pinacol boranes have been described for the preparation of styrenes and derivatives through electrophilic Pd(II) catalysis (Scheme 3.20). ° Treatment of a functionalized allylic precursor with the Pd(II) catalysts listed facilitated an allylic C—H activation. Subsequent transmetallation of the aryl boronic acid and reductive elimination afforded the desired olefin with excellent stereoselectivity. The scope of the transformation allows for a variety of activating and deactivating substituents on the aryl boronic acid as well as numerous functional groups on the starting alkene. A tandem allylic C—H oxidation/vinylic arylation protocol has also been reported. " ... 

Dialkylzinc derivatives can be prepared by a nickel-catalyzed hydrozincation of alkenes. The reaction of Et2Zn with Ni(acac)2 produces nickel hydride that adds to an alkene leading after transmetalation with Et2Zn to a diakylzinc. This reaction takes place in the absence of solvent at temperatures of about 50-60 °C. A number of functionalized olefins, like allylic alcohols or amines, can be directly used, affording the expected products after the quenching with electrophiles in 60-75% yield. This method is especially convenient for the preparation of salt-free functionalized diorganozincs required for the asymmetric addition to aldehydes. ... 

The allylic intermediate 157 was prepared by deprotonation with LDA and reacted with 1,2-dialkyloxiranes in the synthesis of parasorbic acid [132], Direct deprotonation of silyl ally] ether with s-BuLi gave the allylic compound 158, which reacted with electrophiles at the y-position [133]. Tin-lithium transmetallation of a 3-stannylated enamine led to the intermediate 159, which after reaction with electrophiles and acidic hydrolysis gave 3-funcionalized cyclohexenones [134], The chiral mdo-aminoallyllithium 160 was also prepared by tin-lithium transmetallation of the corresponding O-methylprolinol derivative, and alkylated to give after hydrolysis /3-alkylated ketones [135]. Direct deprotonation with t-BuLi of N-methal-lylaniline gave the dianionic intermediate 161, of type XIV [136]. 

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