Propionic acid, 3- dianions

These can be prepared in good yield by reaction of either the mono-anions of trimethylsilyl carboxylates or, preferably, the dianions of carboxylic acids with TMSCI. Acetic and propionic acids give mixtures of O- and C-silylated products. 

Addition of the dianion of /5-sulphinylcarboxylic acids to carbonyl compounds leads to the formation of the corresponding hydroxy derivatives which undergo spontaneous cyclization to give y-lactones440. Bravo and coworkers have found that when optically active ( + )-(R)-3-(p-toluenesulphinyl)propionic acid 426 is used for this reaction, the corresponding diastereoisomeric / -sulphinyl-y-lactones 427 are formed in a ratio which is dependent on the substituents in the carbonyl component441,502 503 (equation 256). 

Aldol-iype Condensation. Dimetalation of (R)-(+)-3-(p-tolylsulfinyl)propionic acid with Lithium Diisopropylamide produces a chiral homoenolate dianion equivalent which reacts with carbonyl compounds to afford p-sulfinyl-y-hydroxy acids these spontaneously cyclize to give the corresponding p-sulfinyl 7-lactones (eq 2) ... 

Reaction of the a-carbanion of an alkyl aryl sulfoxide (RCHzSOAr) with aldehydes may give four dia-stereomers. In general, the reaction is highly diastereoselective with respect to the a-sulfmyl carbon, but poorly diastereofacially selective with respect to attack on the carbonyl component. In fact, the a-carb-anion (31) of benzyl r-butyl sulfoxide adds to an aldehyde to produce only two diastereomers (32a) and (32b). As shown in Scheme 10, the selectivity increases when the counterion is Zn . A transition state structure (33) is proposed to account for the anti stereoselection. ° Addition of the dianion of (/ )-3-(p-to-lylsulfinyl)propionic acid (34) to aldehydes affords two main diastereoisomeric P-(p-tolylsulfinyl)-7-lac-tones (35 R = Ph and Bu , ca. 60 40). These isomers (35) were separated by chromatography, and their... 

Further work on the preparation of cryt/iro-2-alkyl-3-hydroxy-esters (140) by various condensations between propionic acid derivatives and aldehydes has been reported " the use of zirconium enolates seems to be particularly efficacious. Rules for predicting the stereochemical outcome of condensations between lithium enolates of esters and ketones and a-alkoxy-aldehydes have also been delineated. Pure erythro-isomer (140) can also be obtained in some cases by reduction of the corresponding jS-keto-ester with zinc borohydride. In related work it has been found that sodium borohydride in isopropanol reduces t-butyl a-alkoxy-j8-keto-esters to the corresponding -hydroxy compounds with erythro-threo ratios of between 2 1 and 20 1 in favour of the eryt/iro-isomer. In an extension of his previous work, Frdter has reported that dianions derived from cyclohexanol (141) can be alkylated with 95% stereoselectivity, to give (142). When the starting alcohol (141) is optically pure, a sequence of alkylation and oxidation leads to 2-ethoxycarbonylcyclohexanones with 76% enantiomeric enrichments. 

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