Relative energies lithium enolates

SCHEME 107. Relative energies and geometries for the O- and C-addition transition state calculated for the addition of formaldehyde to the lithium enolate of acetaldehyde and the preferred conformations of aldol535... 

TABLE 3. Relative energies (in kcal mol ) of lithium enolates relative to the most stable geometry obtained at different calculahon levels ... 

The reaction is believed to proceed via a six-membered cyclic transition state, analogously to the carbonyl addition of enolates, but the energy differences between boat- and chair-like arrangements are lower for x-sulfinyl carbanions69. Tor tert-butyl sulfoxides only anti- and, vn-products are obtained, arising from the approach onto the same diastereotopic face of the anion, but with different relative topicity. The exchange of lithium by zinc causes an increase of the anft-produci, but attempts to titanate the anion failed (see Table 3)69. 

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