Aldol condensation diastereoselective

Diastereoselective Aldol Condensation with Boron Enolates... 

Diastereoselective aldol condensations.1 The aldol condensation of a chiral ethyl ketone such as 2 with aldehydes catalyzed by Bu2BOTf gives a mixture of all four possible diastereomeric adducts with little or no stereocontrol. In contrast, reactions catalyzed by either (+)- or (- )-l are highly diastereoselective. By proper choice of (+)- and (- )-l and of (+)- and (- )-2, each one of the four possible 1,2-yyn-diastereomers can be obtained in high purity. 

Diastereoselective aldol condensations. This furan (1) can undergo condensation with aldehydes as a butenolide to form 8-hydroxy-a,(3-unsaturated--y-lactones (2). The diastereoselectivity can be controlled by the choice of catalyst. Lewis... 

Diastereoselective aldol condensations and related reactions. The geometry of enolates... 

DIASTEREOSELECTIVE ALDOL CONDENSATION USING A CHIRAL OXA2DLIOINONE AUXILIARY (2S, 3S )-3-HYDR0XY-3-PHENYL-2-METHYLPR0PAN0IC ACID... 

Having identified the (+)-stereoisomer as the biologically active isomer, several independent enantioselective syntheses of this stereoisomer were developed. The initial synthesis developed in discovery chemistry employed the diastereoselective aldol condensation pioneered by Braun as the key component. Thus, treatment of aldehyde 13 from the racemic synthesis with the magnesium enolate of (5)-(+)-2-acetoxy-l,l,2-triphenylethanol at -70 °C, afforded 17 in 60% yield as a 97 3 mixture of the / ,5 5,5-diastereomers by HPLC (Scheme 3). Ester exchange employing sodium methoxide provided the methyl ester in quantitative yield. Reaction of this ester with three equivalents of lithio-f-butylacetate at -40 °C afforded the nearly enantiomerically pure r-butyl ester analog of racemic 14 in 75% yield. 

Diastereoselective aldol condensations.1 The reaction of (S)-( - )-2-benzyl-oxyhexanal (2) complexed with TiCl4 with the bistrimethylsilyl enol ether (1) of methyl acetoacetate gives almost exclusively the syn-aldol adduct (3). This reaction... 

Diastereoselective aldol reaction. Alkyl trityl ketones (2) are readily prepared by reaction of 1 with an aldehyde followed by Cr03 oxidation (50-70% overall yield). Because of steric effects these ketones undergo highly diastereoselective aldol condensation to give syn-adducts (95-99% syn). After protection of the hydroxyl group, the adduct is cleaved by lithium triethylborohydride.1... 

In contrast, fluorinated ketones have been used as both nucleophilic and electrophilic reaction constituents. The lithium (Z)-enolate of l-fluoro-3,3-dimethylbutan-2-one can be selectively prepared and undergoes highly diastereoselective aldol condensation with aldehydes to give products 17. ... 

Among the preformed enol derivatives used for diastereoselective aldol condensations have been enolates of Mg, and silyl enol... 

Diastereoselective aldol condensations continue to attract much attention. - -Alkoxyboronates add to aldehydes at room temperature in the absence of solvent to yield adducts with about 90% dia-stereoselection, dependent upon the initial stereochemistry of the boronate (Scheme 10 cf. Vol.8, p.217). Although relatively sluggish at atmospheric pressure the reactions are accelerated by the... 

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