Abstract
The chiral ligand synthesized from L-diphenylvalinol and salicylaldehyde is found to catalyse the asymmetric Henry reaction with copper(II)acetate monohydrate. Various nitroaldols were formed with 77-95% ee and good yield. The mechanism for the formation of a particular enantiomer is also discussed. The enantioselection in the formation of the chiral nitroaldol is discussed in terms of steric bulkiness of the catalytic system.
Highlights
Among the C-C bond forming reactions, the nitroaldol (Henry) reaction is one of the classical reactions in organic synthesis.[1]
The current study is to identify a weakly Lewis acidic system bearing moderately basic charged ligands that would facilitate the deprotonation of nitroalkanes for the Henry reaction to proceed
In order to test the ability of these ligands to induce enantioselectivity in the copper catalysed asymmetric Henry reaction (Scheme 2), nitromethane and benzaldehyde were made to react with 5 mol% of ligand 2a and the metal salt copper(II) acetate mono hydrate in an ethanolic medium at room temperature
Summary
Among the C-C bond forming reactions, the nitroaldol (Henry) reaction is one of the classical reactions in organic synthesis.[1]. In order to test the ability of these ligands to induce enantioselectivity in the copper catalysed asymmetric Henry reaction (Scheme 2), nitromethane and benzaldehyde were made to react with 5 mol% of ligand 2a and the metal salt copper(II) acetate mono hydrate in an ethanolic medium at room temperature. This resulted in the product (R)-(-)-2-nitro-1-phenylethanol in 60% yield with 40% enantiomeric excess. As a result of this, the yield of the product was decreased to 6% but the enantiomeric excess remained the same (Table 1, entry 3).
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