Allylmetal compounds

Scheme 13.1. Synthesis of homoallylic alcohols by addition of allylmetal compounds to aldehydes.

For reviews on the reactions of allylmetal compounds with aldehydes and imines, see (a) Y. Yamamoto, N. Asao, Chem. Rev. 

Although it is difficult to isolate allylmetal compounds for X-ray studies, azaallyl derivatives, in which CH is replaced by N, are obtained more readily and several have been characterized structurally. 

Allylmetal compounds can be prepared by the Pd-catalysed allylation of dimetal compounds. The phenylallylboronate 195 is prepared by the reaction of 2-phenylallyl acetate with bis(pinacolate)diboron (194) catalysed by ligandless Pd in DMSO [95], A good synthetic route to the allylsilane 197 is the reaction of Me3SiSiMe3 with geranyl trifluoroacetate (196) catalysed by ligandless Pd via transmetallation of the n-allylpalladium intermediate at room temperature in DMF [96],... 

Conjugated dienes undergo metallation to give the 1,4-adduct 198 and the dimerization-1,8-addition product 199 with main group metal compounds. The reaction proceeds by oxidative addition of main group metal compounds to transition metal complexes. Reactive allylmetal compounds 198 and 199 as useful synthetic intermediates are prepared by this methods. 

Catalytic asymmetric allylations of aldehydes or ketones are roughly classified into two methods, namely, those using chiral Lewis acid catalysts and those using chiral Lewis base catalysts. The former method uses less reactive allylsilanes or allylstannanes as the allyl source. The latter method requires allyltrichlorosi-lane or more reactive allylmetals. Both processes are applicable to the reactions with substituted allylmetal compounds or propargylation. 

Nucleophiles such as enolates or substituted allylmetal compounds are known to react with prochiral aldehydes and ketones to form mixtures of threo or erythro adducts. In case of aldehydes, high degrees of diastereoselection have been achieved 48 91,108). In the following three Sections, reactions of titanium and zirconium enolates as well as allyl derivatives are presented. 

Starting with a few reports in the early 1960s, additions of allylmetal compounds to alkenes and al-kynes became increasingly acknowledged. These reactions resemble the classical ene process (Scheme 1), but involve a transfer of a metal instead of a hydrogen. This analogy prompted Of lzer to classify transformations like (A) -h (B) (D), with X = metal, as metallo-ene reactions. However, allylmetal... 

Addition of allylmetal compounds to aldehydes synthesis of homoallylic alcohols 864... 

Catalytic enantioselective allylations of aldehydes already published can be classified into two methods carried out under the influence of chiral Lewis acid catalysts and chiral Lewis base catalysts. The process by chiral Lewis acid catalysts generally uses allyltrimethylsilane or allyltrialkylstannane as an allylating agent, both of which show low reactivity toward aldehydes without these catalysts. The process by chiral Lewis base catalysts employs allyltrichlorosilane or allylmetals possessing relatively higher reactivity. Both processes can be successfully applied to various substituted allylmetal compounds or allenylmetal compounds. 

Allyllithium, prepn. 19, 821 —, syntheses with — 19, 821 Allylmetal compounds... 

Ally derivatives of the alkali metals and alkaline earth metals Dynamic nmr spectroscopy even at very low temperatures shows apparent symmetry for the allylmetal compounds [26] indicating either a very low barrier for the metalomeric equilibrium (33) between degenerate monohapto species [26a] and [26b] or the presence of a n-bridged species [26c] with time-independent symmetry. Deuterium isotope effects on terminal mono-and geminal-dideuteriated allyl compounds of the alkali and alkaline earth metals were investigated to allow distinction between these two possibilities... 

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