| Popis: |
Highly regioselective reductions of ct,13-unsaturated ketones to the corresponding allylic alcohols were performed in essentially quantitative yields in aqueous media containing either glycosidic surfactants or amphiphilic carbohydrates. Reductions of cyclohexanones and cyclohexenones lead under the same conditions, stereoselectively to reduced compounds bearing an equatorial alcohol function. Hydrophobic interactions between amphiphilic carbohydrates and lipophilic substrates were modelized and should account for the observed stereodifferentiation. Organic synthesis in aqueous media has attracted growing attention in the past few years.1 Unfortunately only a few organic compounds display sufficient solubility in water. The use of glyco-organic substrates, which contain a carbohydrate moiety enhancing water solubility and inducing chirality, was thus extensively studied. 1 However easy cleavage of the sugar moiety is a requisite for obtaining the final product. Alternatively, incorporation of the substrate and/or reagent molecules into micelles, microemulsions and various organized assemblies may enlarge the field of organic aqueous reactions. 2 Indeed, micellar aqueous solutions of surfactants proved recently to enhance both the rate and the enantioselectivity of asymmetric hydrogenations promoted by water-soluble rhodium catalysts based on carbohydrates. 20 In this paper, we would like to report on highly regio- and stereoselective reductions of a wide range of carbonyl compounds by sodium borohydride in aqueous solutions containing glycosidic amphiphiles. Our results will be compared with other findings based on the water structure strengthening effects exerted by sugars such as D-glucose. 3 |
Full Text from ScienceDirect