Chiral derivatives carbanion structure

This is an equilibrium reaction, and it raises a couple of points. First, there are two a-positions in the ketone, so what about the COCH3-derived enolate anion The answer is that it is formed, but since the CH3 group is not chiral, proton removal and reprotonation have no consequence. Racemization only occurs where we have a chiral a-carbon carrying a hydrogen substituent. Second, the enolate anion resonance structure with charge on carbon is not planar, but roughly tetrahedral. If we reprotonate this, it must occur from just one side. Yes, but both enantiomeric forms of the carbanion will be produced, so we shall still get the racemic mixture. 

This volume, which complements the earlier one, contains 9 chapters written by experts from 7 countries. These include a chapter on the dynamic behavior of organolithium compounds, written by one of the pioneers in the field, and a specific chapter on the structure and dynamics of chiral lithium amides in particular. The use of such amides in asymmetric synthesis is covered in another chapter, and other synthetic aspects are covered in chapters on acyllithium derivatives, on the carbolithiation reaction and on organolithi-ums as synthetic intermediates for tandem reactions. Other topics include the chemistry of ketone dilithio compounds, the chemistry of lithium enolates and homoenolates, and polycyclic and fullerene lithium carbanions. 

Denmark and coworkers [354] have examined the alkylation of a-lithiated benzyl carbanions generated from diastereoisomeric chiral phosphonamides 1.96 and 5.10. The stereoselectivity of this process depends on the configuration at phosphorus, and it is alway higher when starting from 1.96. It is believed that planar benzylic anions are alkylated on their least sterically hindered face. Strong support for this rationale derives from the X-ray crystal structure of A. After hydrolysis and treatment of the products with diazomethane, (R)- or (S)-dimethyl phosphonates can be obtained (Figure 5.6). Hanessian and coworkers [311, 312] performed similar alkylations of phosphonamides 1.74 (Y = Me, Cl) derived from (RJR)- or ( ,.S)-trans-cyclohexanediamines bearing a C2 axis of symmetry. The reaction of the intermediate anionic species on its less hindered face, followed by... 

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