Asymmetric hydration

Fig. 3.30. Asymmetric hydration of an achiral alkene via hydroboration/oxidation/hydro lysis AFa corresponds to the extent of reagent control of diastereoselectivity.

Scheme 7.86 NHC-catalyzed asymmetric hydration of a,a-dihaloaldehydes or a-fluoroenals reported by Rovis.

An elegant example for this biotransformation is the asymmetric hydration of crotonobetaine yielding the nutraceutical (/ )-camitine (Scheme 2.212), which is used as an additive in baby food, geriatric nutrition and health sport. In order to avoid the undesired degradation of the product, mutant strains lacking carnitine dehydrogenase have been developed at a capacity of >100 t/year [1583-1585],... 

Scheme 2.212 Asymmetric hydration of crotonobetaine to carnitine via a mnltienzyme-system...

Vora, H. U., Rovis, T. (2010). iV-Heterocyclic carbene catalyzed asymmetric hydration direct synthesis of a-protio and a-deuteiio a-chloro and a-fluoro carboxylic acids. Journal of the American Chemical Society, 132, 2860-2861. 

Additional examples of nitrile hydration reactions catalyzed by homogeneous ruthenium catalysts in organic media are (Scheme 8) (1) The hydration of benzoxazolylacetonitrile by the arene-ruthenium(II) dimer [ RuCl(p-Cl)(r -p-cymene) 2], which led to benzoxazolylacetamide in high yield [58], and (2) the asymmetric hydration of a-benzyl-a-methylmalononitrile by the chiral catalysts 13 [59]. Modest yields and low enantiomeric excesses were obtained in this latter reaction. However, we must note that this is the first example of a nonenzymatic asymmetric nitrile hydration process reported to date in the literature. 

Liu (146) used NMR studies to confirm ion associations of the POE chain in solution. Evidence was first found for the binding of potassium iodide in methanol and hydrochloric acid in aqueous solution to poly (ethylene oxide), with the cation being the principal interacting species. These investigations led to conjecture that the mechanism of interaction was akin to that of the crown-ether complexes (147, 148). Sodium-23 NMR measurements have verified the association of the sodium ion with the ether oxygen of the ethylene oxide unit in solvents such as acetonitrile (149). Florin (150) measured NMR relaxation rates for lithium-7, sodium-23, cesium-133, chlorine-35, and bromine-81 complexes and found similar results i.e., there was asymmetric hydration of the ions induced by polyoxyethylene. 

Schnapperelle, 1., Hummel, W., and Groger, H. (2012) Eormal asymmetric hydration of non-activated alkenes in aqueous medium through a chemoenzymatic catalytic system . 

Synthesis of a substituted p-hydroxyphenylethan-1-ol via asymmetric hydration of its corresponding styrene with a recombinant whole-cell catalyst containing a decarboxylase. 

Lei X, Bin J, Li T, Xiao FJ, Mei YH, Ying YJ (2004) Asymmetric hydration of alkenes catalyzed by wool-palladium complex. Polym Adv Technol 15 346-349... 

Wang S, Zhang Z, Chi C, Wu G, Ren J, Wang Z, Huang M, Jiang Y (2008) Asymmetric hydration of ortho- or para-substituted styrenes catalyzed by biopolymer-metal complex wool-Pd. React Func Polym 68 424-430... 

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