A short and efficient synthesis of N-Cbz-galantinic acid under promoter control on enantioselective acyclic stereoselection based on chiral oxazaborolidinone-promoted aldol reactions
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Aldol condensation
Chiral auxiliary
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The enantioselective synthesis of cyclopentanedicarboxylic amino acid 1, a novel rigid and functionalized l-glutamic acid analogue, has been achieved in 15 linear steps from silyloxypyrrole 3, utilizing l-glyceraldehyde 4 as the source of chirality. The key steps in the synthesis are three sequential aldol-based carbon−carbon bond-forming reactions: two crossed vinylogous aldol additions (2 + 3 → 8 and 4 + 5 → 10 + 11) and one intramolecular silylative aldolization (6 → 7). En passant, the short syntheses of (2S)-2-hydroxymethylglutamic acid (16) and its (2R)-enantiomer ent-16, a potent metabotropic glutamate receptor agonist, have been achieved.
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The first enantioselective decarboxylative aldol addition with α-amido-substituted malonic acid half oxyesters (MAHOs) is described. The combined use of a newly designed bifunctional sulfonamide catalyst with pentafluorobenzoic acid as an additive afforded the β-hydroxy-α-amino acid derivatives in moderate to high yields and with high enantioselectivities.
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Malonic acid
Sulfonamide
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Abstract Enantioselective aldol addition to ketones has received growing attention since the resulting tertiary aldols are valuable building blocks for many biologically active compounds. Recently, several catalytic methodologies have been developed based on the activation of acceptor ketones and/or nucleophile enolates, overcoming problems associated with the lower reactivity and decreased steric discrimination of ketones compared to aldehydes. This microreview presents an overview of the progresses in the catalytic enantioselective aldol additions to ketones. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)
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Chiral carbon dots are prepared by a simple and one-step hydrothermal reaction at 180 °C for 2 h using citric acid and d -proline as precursors, which show high asymmetric catalytic activity for enantioselective direct aldol condensation.
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Enantioselective synthesis of both diastereomers including the α-alkoxy-α-methyl-β-hydroxy units has been achieved by the chiral tin(II) Lewis acid-controlled aldol reactions of the silyl enolate derived from p-methoxyphenyl α-benzyloxypropionate (1) with aldehydes.
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Abstract A concise and enantioselective synthesis of ( S )‐ethyl 2‐cyclopentyl‐2‐hydroxy‐2‐arylacetate, a key intermediate for the muscarinic receptor, is reported. The tertiary stereogenic center was constructed with good stereoselectivity through the L‐ proline‐catalyzed direct asymmetric aldol reaction of ethyl arylglyoxylate and cyclopentanone. The carbonyl of the condensation product was reduced using a modified Clemmensen reaction which provided an easier workup and was more environmentally acceptable. The enantioselectivity of the aldol reactions was between 58.3%–93.2%, which means that the stereoselective is efficient in controlling configuration of reaction product.
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Aldol condensation
Cyclopentanone
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