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Dual Proline/Water Compatible Lewis Acid Activation: a Biomimetic Approach for Direct Asymmetric Aldol Reaction
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1  Laboratoire de Chimie Organique et Macromoléculaire UMR8009, Université de Lille 1, Sciences et Technologies – 59655 Villeneuve d’Ascq, France

Abstract: A novel approach based on combinations of various water compatible Lewis acids and L-proline cocatalysts has been evaluated for the direct asymmetric aldol reaction. From this screening zinc (II) chloride salts lead to the highest stereoselectivities. Optimized catalytic conditions (Catalytic system : L-proline : 20 (percent) / ZnCl2 : 10 (percent) - Solvent mixture : DMSO/H2O – 8 : 2) give anti aldol product with improved enantioselectivity (>99 (percent) e.e.) compared to a moderately stereoselective procedure based on proline activation only.