Grignard reagents allylic substitution

Next, reaction with a silicon-substituted Grignard reagent in the presence of Ni(II) gives an allyl silane. What kind of reaction is this, what was the role of phosphorus, and why was a metal other than sodium added (You know nothing specific about Ni as yet but you should see the comparison with another metal. Consult Chapter 23 if you need help.)... 

Acetals as Chiral Auxiliaries. There have been many applications of acetals of 2,4-pentanediol as chiral auxiliaries to control the diastereoselectivity of reactions on another functional group. Examples include cyclopropanation of alkenyl dioxanes, lithium amide-mediated isomerization of epoxides to allylic alcohols, and addition of dioxane-substituted Grignard reagents or organolithiums to aldehydes. 

In 1999, Ikeda et al. reported a new type of sulfur-oxazoline ligands with an axis-fixed or -unfixed biphenyl backbone prepared in good yields by coupling reactions of methoxybenzene derivatives substituted with a chiral oxazoline and a sulfur-containing Grignard reagent. These ligands were subsequently evaluated for the test palladium-catalysed asymmetric allylic alkylation... 

More recently, Backvall et al. have reported the use of arenethiolatocopper(I) as a catalyst for the analogous substitution reaction of Grignard reagents with allylic substrates. In this case, the crosscoupling reaction could occur in an a(SN2) or y(Sn2 ) manner, depending on the reaction conditions. In all cases, the y-product was isolated as the sole product with moderate to quantitative... 

In the 1952 paper mentioned above [3], Gilman reported on the formation of lithium dimethylcuprate from polymeric methylcopper and methyllithium. These so-called Gilman cuprates were later used for substitution reactions on both saturated [6] and unsaturated [7, 8, 9] substrates. The first example of a cuprate substitution on an allylic acetate (allylic ester) was reported in 1969 [8], while Schlosser reported the corresponding copper-catalyzed reaction between an allylic acetate and a Grignard reagent (Eq. 2) a few years later [10]. 

Initial studies on the application of these catalysts to allylic substitution reactions showed that the arenethiolate moiety functions as an excellent nontransferable group, and that the regioselectivity can be completely reversed by suitable changes in the reaction parameters [33]. If the reaction between geranyl acetate and n-BuM gl was carried out inTHFat—30°C with fast addition of the Grignard reagent to the reaction mixture, complete a selectivity was obtained. Raising the tempera-... 

The effect of the leaving group was briefly examined, but cinnamyl bromide gave a substantially lower ee (38%). Cinnamyl dimethyl phosphonate, or acetate, gave very poor results. The cyclohexyl-substituted allylic acetate 21, on the other hand, afforded a completely y-selective reaction, but the product turned out to be racemic. Changing the Grignard reagent halide from bromide to either chloride or iodide resulted in very low ees. 

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