Metal ynolates preparation

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. 

The a-chloro-a-sultinyl ketone 20 was prepared from methyl benzoate and chloromethyl phenyl sulfoxide 19 after in situ a-lithiation. Compound 20 is dimetallated by KH and f-BuLi to give the keto dianion 21, which is converted into a potassium/lithium ynolate 22 (equation 7). The resulting metal ynolates are converted into thioesters, carboxylic acids, amides and esters (Section V). 

Metal ynamines (metal ynamides, 180) are aza-analogues of metal ynolates and have not been studied as well as the ynamines (181), in spite of being much more reactive than the latter. l,4-Diphenyl-l,2,3-triazolyllithium (183), prepared by lithiation of 1,4-diphenyl-1,2,3-triazole (182), is converted into lithium ynamine (lithium ynamide) (184) on thermal elimination of nitrogen (equation 72). This ynamine (184) is methylated in moderate yields either by methyl iodide to give a ketenimine (185) and a dimerization product (186), or... 

In contrast with the vast array of known alkyl or aryl alcohols/ethers, relatively scant attention has been paid to ynols and related compounds. This is due, in part, to the rapid conversion of formal ynols into ketene tautomers. It should be noted that metal ynolates can be readily generated and used for organic transformations [187]. For ynol ethers, a relatively small number of approaches are known for the preparation of these compounds. The following sections will highlight modifications made to this system as well as new methods for generating oxygen-carbon (sp ) bonds. 

Lithium phenylethynolate (520) has been prepared in a rather intriguing fashion through the elimination of benzonitrile from 5-lithio-3,4-diphenylisoxazole (519) (75AG(E)765). Reaction of the ynolate with an aldehyde or ketone was shown to afford a metallated /3-lactone (521). Treatment of this intermediate in turn with an electrophilic reagent such as benzyl bromide produced a tri- or tetra-substituted /3-lactone (522 Scheme 114). 

S -Analogues of lithium or sodium ynolates (thioalkynolates or alkynethiolates) are prepared from lithium or sodium acetylide and sulfur, and are trapped as alkynyl sulfides with bromoethane (equation 77). In a synthetic approach analogous to equation 72, 5-lithio-l,2,3-thiadiazoles (198) also afford lithium alkynethiolates (199) by elimination of nitrogen (equation 78) . Alkynyl sulfides (200) are treated with lithium in ammonia to afford lithium alkynylthiolates (199) (equation 79) °. Theoretical studies on the structure of alkali metal alkynylthiolates are reported. ... 

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