Alkali metal enolates from ketenes

When the preparation of alkali metal enolates derived from alkanoylphosphonates was attempted by treatment with strong anhydrous bases such as lithium diisopropylamide or sodium hydride, the formation of phosphate phosphonate-type products was observed. This was interpreted in terms of fragmentation of the enolate formed in the first step to ketene and dialkyl phosphite anion (equation 75), and addition of the latter to the carbonyl group of an unreacted acylphosphonate molecules to form a bisphosphonate. Such molecules are known to rearrange to phosphate phosphonates ... 

Among alkali metal enolates, those derived from ketones are the most robust one they are stable in etheric solutions at 0 C. The formation of aldehyde enolates by deprotonation is difficult because of the very fast occurring aldol addition. Whereas LDA has been reported to be definitely unsuitable for the generation preformed aldehyde enolates [15], potassium amide in Hquid ammonia, potassium hydride in THE, and super active lithium hydride seem to be appropriate bases forthe metallation of aldehydes [16]. In general, preformed alkali metal enolates of aldehydes did not find wide application in stereoselective synthesis. Ester enolates are very frequently used, although they are more capricious than ketone enolates. They have to be formed fast and quantitatively, because otherwise a Claisen condensation readily occurs between enolate and ester. A complication with ester enolates originates from their inherent tendency to form ketene under elimination... 

Metal ynolates are not as easy to prepare in a similar fashion as metal enolates, because the intermediates may be labile monosubstituted ketenes. Several preparative methods for alkali metal ynolates have been reported, among which some have been used as intermediate steps in one-pot organic syntheses. Silyl ynolates have been prepared from lithium ynolates. There have been few reports on the other metal ynolates. Since there is no universal method to determine the yield of metal ynolates, the efficiency of preparation is estimated from the results of some of the following reactions. 

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