Ethyl carbanion

Saunders (1997) investigated this possibility by calculating the structure of three fluorine-substituted ethyl carbanions, [12]-[14], at the MP2/6-31 + G //MP2/6-31 + G level. 

Difluoromethylene groups flanking the double bond decrease the electron density of the bond and thus activate it for nucleophilic reactions. The nucleophile here is ethyl carbanion, which adds to the double bond. Chlorine atom, linked to the same carbon, is eliminated, and thus 1-chloro-2-ethylhexafluorocyclopentene is formed. 

Like carbocations, carbanions are also stabilized by resonance. Thus, benzyl carbanion and allyl carbanion are more stable than ethyl carbanion. The stabilization by resonance is due to the delocalization of the negative charge, which is distributed over other carbon atoms. The canonical (resonating) forms of benzyl carbanion and allyl carbanion are given below ... 

The alcohol is the stronger acid, and ethyl carbanion is the stronger base ... 

The first step is the interaction of the basic catalyst with the ester to produce the carbanion (I) the carbanion so formed then attacks the carbonyl carbon of a second molecule of ester to produce the anion (II), which is converted to ethyl acetoacetate (II) by the ejection of an ethoxide ion. Finally (III) reacts with ethoxide ion to produce acetoacetic ester anion (IV). This and other anions are mesomeric thus (IV) may be written ... 

It may be pointed out that C-alkylation of ethyl acetoacetate is readily aooount for by the mesomeric nature of the carbanion (IV), as will be evident from the following ... 

Carbon is alkylated ia the form of enolates or as carbanions. The enolates are ambident ia activity and can react at an oxygen or a carbon. For example, refluxing equimolar amounts of dimethyl sulfate and ethyl acetoacetate with potassium carbonate gives a 36% yield of the 0-methylation product, ie, ethyl 3-methoxy-2-butenoate, and 30% of the C-methylation product, ie, ethyl 2-methyl-3-oxobutanoate (26). Generally, only one alkyl group of the sulfate reacts with beta-diketones, beta-ketoesters, or malonates (27). Factors affecting the 0 C alkylation ratio have been extensively studied (28). Reaction ia the presence of soHd Al O results mosdy ia C-alkylation of ethyl acetoacetate (29). 

The formation of ethyl cyano(pentafluorophenyl)acetate illustrates the intermolecular nucleophilic displacement of fluoride ion from an aromatic ring by a stabilized carbanion. The reaction proceeds readily as a result of the activation imparted by the electron-withdrawing fluorine atoms. The selective hydrolysis of a cyano ester to a nitrile has been described. (Pentafluorophenyl)acetonitrile has also been prepared by cyanide displacement on (pentafluorophenyl)methyl halides. However, this direct displacement is always aecompanied by an undesirable side reaetion to yield 15-20% of 2,3-bis(pentafluoro-phenyl)propionitrile. 

The mechanism of the Feist-Benary reaction involves an aldol reaction followed by an intramolecular 0-alkylation and dehydration to yield the furan product. In the example below, ethyl acetoacetate (9) is deprotonated by the base (B) to yield anion 10 this carbanion reacts with chloroacetaldehyde (8) to furnish aldol adduct 11. Protonation of the alkoxide anion followed by deprotonation of the [i-dicarbonyl in 12 leads to... 

The thenyl cyanides are of great importance for the preparation of thiophene derivatives. Because of the acidifying effects of both the thienyl and of the cyano groups, carbanions are easily obtained through the reaction with sodamide or sodium ethoxide, which can be alkylated with halides, carbethoxylated with ethyl carbonate, or acylated by Claisen condensation with ethyl... 

The carbanions derived from acylthiophenes have been condensed with aldehydes,and, through the Claisen condensation with esters, thienylsubstituted -diketones have been obtained. 2-Thenoyl trifluoroacetone, first prepared by Reid and Calvin through the Claisen condensation of 2-acetylthiophene with ethyl trifluoracetate, has become an extremely useful chelating agent for the extraction of numerous elements from strongly acidic solutions, The tautomeric form which dominates in aqueous solution is the ketone hy-drate. Other thiophenes have also proved useful for analytical purposes. ... 

A great number of N-substituted 4-hydroxy-3-nitro-l,8-naphthyridin-2 (IH)-ones are obtained by reaction of N-substituted azaisatoic anhydrides with ethyl nitroacetate carbanion (Section II,A,4,a). A very specific method, more recently developed, is that of the inverse Diels-Alder method, involving the reactions of enamines with 5-nitropyrimidine (Section II,A,4,b). 

Treatment of 1-arylsulfonylpipecolinamides 46 with excess EDA gave pyrido[l,2-ft][l,2]benzothiazine 5,5-dioxides 47 in a carbanion-mediated reaction (97SL1079, 98MI2). When the reaction mixture of 46 (R = Me, R = H) was quenched with Mel an ethyl derivative 47 (R = Et, R = H) was obtained. 

Treatment of 49 with a strong base such as sodium ethoxide serves to remove the last proton on the heterocyclic ring. Alkylation of the resulting carbanion with allyl bromide affords aloxidone (50) methyl sulfate on the carbanion gives trimetha-dione (51), while ethyl sulfate yields paramethadione (52). ... 

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