Enolates, lithium salts, aldol condensation with

Enolates, lithium salts, aldol condensation with, 54, 49 Enol esters, preparation, 52,... 

It is not clear whether enolization is avoided under the lithium-free, high-concentration conditions, or whether it occurs reversibly enough to permit eventual conversion of the ketone to the alkene. However, the most successful procedures involve alkoxide bases (159, 168-170) or require the presence of excess phosphonium salt (171). Proton exchange and reversible enolate formation are likely under these conditions, and aldol condensation pathways would also be reversible when potassium or sodium bases are used. Thus, excellent yields of alkenes are possible with the most hindered substrates, provided that other pathways for irreversible enolate decomposition are not available. 

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