Alkaline earth metal enolates

Alkali alkaline earth metal enolates tend to be aggregates- complicates stereo selection models. 

The addition of an alkaline earth metal enolate A to a carbonyl compound is always an exer-gonic process irrespective of whether the enolate is derived from a ketone, an ester, or an amide and whether the carbonyl compound is an aldehyde or a ketone (Figure 13.44, top). One of the reasons for this exergonicity hes in the fact that the alkaline earth metal ion is part of a chelate in the alkoxide B of the aldol addition product. The driving forces for the additions of alkaline earth metal enolates of esters and amides to carbonyl compounds are further increased because the aldol adducts B are resonance-stabilized, whereas the enolates are not. 

Starting from /l-ketoesters (Figure 10.4, see Figure 10.22 for a synthetic application), or /l-ketoaldehydes (Figure 10.5), ammonium enolates are formed with a stereostructure ( -enolates) that differs from that of the corresponding alkaline earth metal enolates (Z-enolates). In the latter, the lithium atom forms a bridge between the two neg-... 

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