Esters reaction with carboxylic acid dianions

B-alkyl-9-BBN derivatives (p. 1077). Since only the 9-alkyl group migrates, this method permits the conversion in high yield of an alkene to a primary alcohol or aldehyde containing one more carbon." When B-alkyl-9-BBN derivatives are treated with CO and lithium tri-ferf-butoxyaluminum hydride," other functional groups (e.g., CN and ester) can be present in the alkyl group without being reduced." Boranes can be directly converted to carboxylic acids by reaction with the dianion of phenoxyacetic acid." " ... 

Carboxylic acid derivatives such as esters and amides undergo nucleophilic acyl substitution reactions with the ketone dianion derived fiom benzophenone, providing modest yields of the corresponding carbonyl products (equations 102 and 103). Benzhydrol is a significant by-product in these reactions. 

Nitroalkenes react with lithium dianions of carboxylic acids or with hthium enolates at -100 °C, and subsequent treatment of the Michael adducts with aqueous acid gives y-keto acids or esters in a one-pot operation, respectively (Eq. 4.52).66 The sequence of Michael addition to nitroalkenes and Nef reaction (Section 6.1) provides a useful tool for organic synthesis. For example, the addition of carbanions derived from sulfones to nitroalkenes followed by the Nef reaction and elimination of the sulfonyl group gives a,P-unsaturated ketones (Eq. 4.53).67... 

Enolate hydroxylation is a problem of long standing. Direct oxygenation succeeds with the fully substituted enolates of certain a,a-disubstituted ketones and a variety of carboxylic acid derivatives (ester anions, acid dianions, amide anions), but the reaction of enolates, RCH = C(0 )R or CH2 = C(0 )R, with oxygen results in complex products of overoxidation. The stable... 

Carboxylic acids can be alkylated in the a position by conversion of their salts to dianions [which actually have the enolate structures RCH=C(0 )21497] by treatment with a strong base such as lithium diisopropylamide.1498 The use of Li as the counterion is important, because it increases the solubility of the dianionic salt. The reaction has been applied1499 to primary alkyl, allylic, and benzylic halides, and to carboxylic acids of the form RCHjCOOH and RR"CHCOOH.1454 This method, which is an example of the alkylation of a dianion at its more nucleophilic position (see p. 368), is an alternative to the malonic ester synthesis (0-94) as a means of preparing carboxylic acids and has the advantage that acids of the form RR R"CCOOH can also be prepared. In a related reaction, methylated aromatic acids can be alkylated at the methyl group by a similar procedure.1500... 

It can be assumed that the small amount of piperidine in the reaction mixture is completely protonated by malonic acid because piperidine is more basic than pyridine. Hence, only the less basic pyridine is available for the formation of the malonic acid enolate D from free malonic acid and for the formation of the malonic acid dianion from the malonic acid mono-carboxylate C. The pKa value of malonic acid with regard to its C,H acidity should be close to the pKa value of malonic acid diethyl ester (p= 13.3). The pKa value of malonic acid monocarboxylate C with regard to its C,H acidity should be larger by at least a factor 10. Hence, the concentration of the malonic acid enolate D in the reaction mixture must be by many orders of magnitude higher than that of any malonic acid dianion. Due to the advantages associated with this enormous concentration D could be the actual nucleophile in Knoevenagel condensations. 

P-Keto acids. A new synthesis of /i-keto acids involves the reaction of dianions of carboxylic acids with esters.6 The intermediates are trapped with trimethylchlorosilane and isolated as the trimethylsilyl esters. For example, isobutyric acid is converted into the dianion (1) by treatment with 2 eq. of lithium diisopropylamide in THF at 0°. Addition of I eq. of methyl pivalate (2) and an excess of trimethylchlorosilane yields the... 

Epoxides - The first indication of the synthetic utility of metalated carboxylic acids resulted from efforts to prepare steroidal aldosterone inhibitors from spiroepoxides.39 Model studies indicated that the reaction fails as a result of severe steric hindrance in either the epoxide or carboxylic acid and that monosubstitution occurs for the same reason.39 The reaction has been used in a key step of an elegant synthesis of vernolepin, 5. 40 Forcing conditions are required, and, in contrast to acid dianions, anions of unactivated esters fail to react with epoxides.39 41... 

In a novel alkylating method that has been published, the dianion of carboxylic acid (177) was subjected, in a first step, to a nucleophilic addition reaction with the Cjo aldehyde ester (169) to give the unstable hydroxy acid (178) (Trost and Fortunak, 1981). The acetylated acid (179) smoothly underwent decarboxylative elimination to give ethyl retinoate (24). 

Anionic Reactions. In a manner similar to o -silyl esters, trimethylsilylacetic acid (1) can be used to prepare a,fi-unsaturated carboxylic acids from carbonyl compounds by a Peterson alkenation reaction (eq 1). However, the dianion of acid (1) is required. The yields are generally inferior to analogous reactions with a-silyl esters. ... 

The electrochemical reaction of organoboranes in the presence of propenoic acid esters has been reported to be a convenient synthesis of carboxylic esters while with acetone, trialkylboranes react electrochemically to yield dioxaboro-lanes (6) and dioxaborinanes (7) [reaction (3)]. The first direct synthesis of carboxylic acids from organoboranes has been published and involved the reaction of trialkylboranes and the dianion of phenoxyacetic acid in THF [reaction (4)]. ... 

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