Acetals acetoacetate carbanions

Acetone cyanohydrin nitrate, a reagent prepared from the nitration of acetone cyanohydrin with acetic anhydride-nitric acid, has been used for the alkaline nitration of alkyl-substituted malonate esters. In these reactions sodium hydride is used to form the carbanions of the malonate esters, which on reaction with acetone cyanohydrin nitrate form the corresponding nitromalonates. The use of a 100 % excess of sodium hydride in these reactions causes the nitromalonates to decompose by decarboxylation to the corresponding a-nitroesters. Alkyl-substituted acetoacetic acid esters behave in a similar way and have been used to synthesize a-nitroesters. Yields of a-nitroesters from both methods average 50-55 %. 

Total synthesis is applied for carotenoids on a lO t scale per year. One usually starts with the cheapest carbonyl components (formaldehyde, acetone) and carbanions (acetylide, acetoacetate, cyanide, Wittig ylides) available. A typical industrial synthesis of retinol acetate (vitamin A) is outlined in Scheme 5.3,1. 

After these initial results by Tsuji, this elementary step was incorporated into a catalytic process by Hata and co-workers at Toray Industries and by Atkins and co-workers at Union Carbide. These groups reported reactions of allylic phenyl ethers, allylic alcohols, and allylic acetates with carboxylates, alcohols, primary and secondary amines, and methyl acetoacetate catalyzed by Pd(0) complexes and precursors to Pd(0) complexes (Equation 20.3). - After these initial reports, early developments focused on reactions of "soft" carbanions derived from 3-dicarbonyl compounds, cyanoesters, and related compounds containing two electron-withdrawing groups attached to the nucleophilic carbon. Although these reactions occur with allylic halides in the absence of a catalyst, these reactions are greatly accelerated by palladium catalysts. Thus, the palladium catalyst allows these reactions to occur under mild conditions with allylic acfetates, which are more accessible than allylic halides, and with selectivities that are altered by the metal catalyst. 

Scheme 9.145. A representation of proton removal from the methyl group of ethyl ethanoate (ethyl acetate, CH3CO2CH2CH3) generating a resonance-stabilized carbanion. Attack of the latter at the carbonyl of ethyl benzenecarboxylate (ethyl benzoate, C6H5CO2CH2CH3) and ethyl ethanoate (ethyl acetate, CH3CO2CH2CH3) to yield, respectively, ethyl 3-phenyl-3-oxopropanoate and 3-oxobntanoate (ethyl acetoacetate, CH3COCH2CO2CH2CH3). An example of the Claisen condensation.

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