Enol acetates alkali metal enolates

The Mechanism of the Ethyl Acetoacetate Synthesis—Before the tautomerism of ethyl acetoacetate is discussed we must consider the mechanism of its formation, which for decades has been the subject of lively discussion and was conclusively explained only in recent years (Scheibler). It has been found that even the C=0-group of the simple carboxylic esters, although in other respects inferior in activity to the true carbonyl group, can be enolised by alkali metals. Thus ethyl acetate is converted by potassium into the potassium salt of the tautomeric enol with evolution of hydrogen ... 

The present procedures illustrate general methods for the use of preformed lithium enolates5 as reactants in the aldol condensation6 and for the quenching of alkali metal enolates in acetic anhydride to form enol acetates with the same structure and stereochemistry as the starting metal enolate.7 The aldol product, [Pg.55]

Alkali Metal Enolates from Enol Acetates and Silyl Eru>l Ethers 1.423 Alkali Metal Enolates by Miscellaneous Methods... 

Alkali Metal Enolates by Cleavage of Enol Acetates or Silyl Enol Ethers... 

The mechanism and thermodynamics of transesterification of acetate-ester enolates in the gas phase have been investigated. The catalytic effect of alkali-metal t-butoxide clusters on the rate of ester interchange for several pairs of esters has been determined in non-polar and weakly polar solvents. Reactivities increase in the order (Li+ < Na+ < K+ < Rb+ < Cs+) with the fastest rates reaching lO catalytic... 

The base-catalysed degradation of the ring of isoxazolium salts is particularly easy, requiring only alkali metal carboxylates to achieve it. The mechanism, illustrated for the acetate-initiated degradation of 2-methyl-5-phenylisoxazolium iodide, involves initial 3-deprotonation with cleavage of the N-O bond subsequent rearrangements lead to an enol acetate which rearranges to a final keto-imide. 

The Pd-catalyzed reaction of the acetone-derived enolate presumably containing an alkali metal countercation with allyl acetate was reported in 1980 to give a 2 1 mixture of the diallylated and monoallylated products (Scheme 1). A year later, the reaction of lithium enolates of a few ordinary ketones with allyhc acetates under the influence of 1 mol % each of Pd(dba)2 and dppe was reported to give the desired monoalkylated products mostly in moderate yields with no specification of the extents of diallylationf (Scheme 2). 

An isolated acetoxyl function would be expected to be converted into the alkoxide of the corresponding steroidal alcohol in the course of a metal-ammonia reduction. Curiously, this conversion is not complete, even in the presence of excess metal. When a completely deacetylated product is desired, the crude reduction product is commonly hydrolyzed with alkali. This incomplete reduction of an acetoxyl function does not appear to interfere with a desired reduction elsewhere in a molecule, but the amount of metal to be consumed by the ester must be known in order to calculate the quantity of reducing agent to be used. In several cases, an isolated acetoxyl group appears to consume approximately 2 g-atoms of lithium, even though a portion of the acetate remains unreduced. Presumably, the unchanged acetate escapes reduction because of precipitation of the steroid from solution or because of conversion of the acetate function to its lithium enolate by lithium amide. 

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