Lithiation allyllithium compounds

This test showed that a-amino- [7] and a-oxy- [8] alkyllithium compounds except for their benzyl- or allyllithium compounds are configurationally highly stable, and a-thio-[9], a-selenoalkyllithium compounds [10], and lithiated phosphine oxides [11] are labile. Thus, this test proves that lithium carbanions are either configurationally stable or labile and affords reliable evidence to de-... 

Allyltitanium reagents have been used in the homo-aldol reaction [76]. Enan-tiodivergent tuning by virtue of the titanium reagents of chiral l-oxyallyUithium substrates leads to enantiomeric homo-aldol products with excellent enantiomeric excess. Hoppe and coworkers found the first example of a chiral nonracemic allyllithium with configurative stabiHty [77]. In their work they described the lithiation of optically pure aUyl carbamates. These lithiated allylic carbamates are substrates for homo-aldol reactions. The so-derived chiral allyllithium compounds can be transmetaUated to titanium in order to facilitate a subsequent aldol reaction (Scheme 3.48) [76a]. 

Functionalized allyllithium compounds of type XIII are also homoenolate equivalents [122,130], but in their reaction with electrophiles sometimes it is not possible to control the regioselectivity. These compounds have been prepared mainly by either deprotonation or tin-lithium exchange. Deprotonation of (F)-cinnamyl-N,N-diisopropylcarbamate 155 with n-BuLi in the presence of (-[-sparteine in toluene gave a configurationally stable lithiated O-allyl carbamate (epi-156), which equilibrates at -50 °C to give the (R)-intermediate 156. Whereas the reaction of these compounds with Mel and MeOTs gave the /-attack, however acylation, silylation and stannylation took place at the a-position (Scheme 2.21) [131]. 

Allylthiopyridines such as compound 125 undergo reductive lithiation on treatment with lithium and 4,4 -di-tert-butyldiphenyl (DBB) and the resulting allyllithium reacts with TMSC1 to give allylsilanes such as 126 <2004JOC7592>. (Equation 90). 

Although allylic lithiation by deprotonation of non-heterosubstituted compounds is possible using superbases (see section 2.6), in most cases allylic lithiation requires a directing heteroatom. (Non-heterosubstituted allyllithiums are best produced by reductive lithiation of allyl ethers or allyl sulfides - see section 4.4.) One of the few cases where this heteroatom is not a to the new organolithium is shown below the p-lithiation of a homoallylic amide 137. The reaction is particularly remarkable because of the possibility of competing deprotonation... 

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