Allyl lithium addition

The addition of anhydrous cadmium iodide or chloride on allylic lithium carbanions causes changes in the regioselectivity, but information on the stereochemical results is scarce31-42-43. 

Addition of l,3-bis(methylthio)allyllithium to aldehydes, ketones, and epoxides followed by mercuric ion-promoted hydrolysis furnishes hydroxyalkyl derivatives of acrolein5 that are otherwise available in lower yield by multistep procedures. For example, addition of 1,3-bis-(methylthio)allyllithium to acetone proceeds in 97% yield to give a tertiary alcohol that is hydrolyzed with mercuric chloride and calcium carbonate to saturated aldehyde.8 Similarly, addition of l,3-bis(methylthio)allyl-lithium to an epoxide, acetylation of the hydroxyl group, and hydrolysis with mercuric chloride and calcium carbonate provides a 5-acetoxy-a,/ -unsaturatcd aldehyde,6 as indicated in Table I. Cyclic cis-epoxides give aldehydes in which the acetoxy group is trans to the 3-oxopropenyl group. 

The propargylic alcohol group may be exploited as an allylic alcohol precursor (Eq. 6A.2) and may be generated by nucleophilic addition to an electrophile [25] or by addition of a formaldehyde equivalent to a preexisting terminal acetylene group [26], Once in place, reduction of the propargylic alcohol with lithium aluminum hydride or, preferably, with sodium bis(2-methoxyethoxy)aluminum hydride (Red-Al) [27] will produce the trans allylic alcohol. Alternately, catalytic reduction over Lindlar catalyst can be used to obtain the cis allylic alcohol [28]. The addition of other lithium acetylides to ketones produces chiral secondary alcohols, which also can be reduced by the preceding methods to the cis or trans allylic alcohols. Additional synthetic approaches to allylic alcohols may be found in the various references cited in this chapter. 

Hay and co-workers reported that the Mn increased linearly with conversion at a molar ratio of 1 2. However, at high ratios of n-BuLi to TMEDA, the initiator became only 50% efficient. This finding is rather surprising as the addition of TMEDA to alkyllithium compounds enhanced the rate of the polymerization and without TMEDA, at Hay s polymerization temperature, no polymerization of the 1,3-butadiene took place. The explanation advanced by these authors was that the allylic lithium complex of polybutadiene is complexed with two TMEDA molecules and that complex 11 is the propagating species. 

As may be seen from Fig. 3, there are no resonance peaks at 120-128 ppm characteristic of 1,4-microstructure in polybutadiene polymer. However, on addition of methanol to the chain live ends, resonance peaks at 120-128 ppm appear in ratios of 60% trans-1,4, 14% m-1,4, and 26% 1,2. This suggests that the protonation of the chain live ends with methanol is an independent reaction and does not relate to the actual structure of the propagating species. It may be said that the structure of the allylic lithium of polybutadiene (DP > 1) is postulated to exist in the 1,2-form (13). Yet hydrolysis of 13 gives mixed 1,4- and 1,2-microstructures. 

Gajewski has examined the secondary deuterium isotope effects in the addition of allyllithium and allyl Grignard additions to benzaldehyde [157]. With allyl-lithium and allylmagnesium halides a normal secondary deuterium isotope effect was observed. The results indicate that rate-determining single-electron transfer occurs with the allyl reagents. 

The most useful of all allyl anion equivalents are the allyl silanes.20 This is because it is easy to make them regioselectively, because they do not undergo allylic rearrangement (silicon does not do a [1,3] shift) and because their reactions with electrophiles are very well controlled addition always occurring at the opposite end to the silicon atom. Symmetrical allyl silanes can be made from allyl-lithiums or Grignards by displacement of chloride from silicon. A useful variant is to mix the halide with a metal, e.g. sodium, and Me3SiCl in the same reaction, rather after the style of the silicon acyloin reaction,21 as in the synthesis of the acetal 80. 

Just as anions of allyl derivatives can be homoenolate equivalents (chapter 13) so anions of vinyl derivatives can be acyl anion equivalents. Vinyl (or enol) ethers can be lithiated reasonably easily, especially when there is no possibility of forming an allyl derivative, as with the simplest compound 81. The most acidic proton is the one marked and the vinyl-lithium derivative 82 reacts with electrophiles to give the enol ether of the product17 84. However, tertiary butyl lithium is needed and compounds with y-CHs usually end up as the chelated allyl-lithium 85. These vinyl-lithium compounds add directly to conjugated systems but the cuprates will do conjugate addition.18... 

Such a mechanism has been demonstrated in the addition of dithianyl allyl lithiums [199]. 

Scheme 5.39. Allyl sulfoxide additions , fa 1,4-mechanism [198]. (b) Tandem 1,2-addition / 3,3-rearrangement mechanism [148] (see also ref. [199]). (c,d) Transition structures for allyl phosphine oxides [196,197]. Inset Gauche pentane interaction between lithium and the N/je methyl.

The addition of allylic organometallic reagents to aldehydes and ketones is another route to -unsaturated alcohols. A new preparation of allyl-stannanes, and hence of allyl-lithium species (Scheme 13), is useful where direct lithiation to... 

In connection with investigations on the catalytic activity of organometallic compounds of the rare earths, anionic homoleptic allyl derivatives of Ce, Nd, Sm, Gd and Dy have been prepared according to eq. (47). Allyl lithium was generated in situ from Sn(C3Hj)4 and another lithium alkyl LiL. The compounds, isolated as their dioxane complexes after precipitation from ethereal solution by addition of dioxane, are described as containing fluxional allyl groups from their infrared and H NMR spectra (Mazzei, 1979) ... 

Allylsilanes result from allyl sulphides which have siloxy subsdtuents with regio and stereochemically using allyl-lithium, from alkenyl Fischer carbene complexes with silanes through addition of Si-H to the carbene, and opdcally active y-silylallylamines result frnn a n-allylPd intermediate obtained from the carbonate using amines or azide, while allyldichlorosilane can be prepared by the direct method at 220 - 320 C as the main product. The protodesilyladon of allylsilanes provides a route to vinyl sulphones while silylmethyl allyl sulphones result from silylmethyl cuprates and sulphonylalka-1,2-dienes, and are used in the... 

As shown in Scheme 3.1 [63], organolithium compounds in hydrocarbon solvent exist largely in the form of tetramers or hexamers. Initiation apparently occurs when a monomolecular species in equilibrium with the associated species adds to the 1,4- of butadiene to give an allylic lithium compound, which propagates by repeated 1,4-addition until all butadiene is consumed. The intermediate allylic lithium compounds are stable enough to remain active at room temperature almost indefinitely [63]. 

Allylmagnesium bromide, allyl-lithium, and n-butyl-lithium react with the alcohol (598) mainly by monoaddition to the double bond, whereas with allylzinc bromide, mono- and bis-addition to the triple bond occur (Scheme... 

Anionic Additions to Aldehydes. The addition of l,3-bis(silyl)-propenes to aldehydes and ketones to yield the vinyl silyl alcohol was explored. This was done using TBAF and good to excellent yields were achieved (eq 11). A further extension of this work was the addition of the (l,3-bis(silyl)allyl)lithium to ketones and aldehydes (eq 12). In this reaction, the substituted silyl diene was isolated in moderate to good yields. These substrates were then explored as ligands for both iron and manganese complexes. 

R. A. Benkesar, M. P. Sikosi, and E. C. Mozdzen, /. Amer. Chem. Soc., 1978, 100, 2134. Effect of steric hindrance on the reversible addition of allylic-lithiums to ketones. 

The addition products of [l,3-bis(phenylseleno)allyl]lithium and electrophiles may be converted, in high yields, into unsaturated aldehydes, this now being the subject of a full paper. The versatile sulphoxide-sulphenate rearrangement provides the regio- and stereo-control in a route to -substituted ( )-l-aryl-enones (Scheme 30). -Substituted enones may also arise from alkylation of... 

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