Aqueous-phase asymmetric transfer hydrogenation of ketones--a greener approach to chiral alcohols
1Liverpool Centre for Materials and Catalysis, Department of Chemistry, University of Liverpool, Liverpool, UK.
Abstract:
Asymmetric transfer hydrogenation (ATH) has emerged as a practical, powerful alternative to asymmetric hydrogenation for the production of chiral alcohols, one of the most valuable intermediates in chemical synthesis. In the last a few years, ATH in neat water has proved to be viable, affording chiral alcohols in fast rates, high productivity and high enantioselectivity. The reduction can be carried out with unmodified or tailor-made catalysts by using mild, readily available formate salt as reductant with no organic solvents required, thus providing a simple, economic and green pathway for alcohol production. This Feature Article attempts to present an account of the progress made on aqueous-phase transfer hydrogenation (TH) reactions, with a focus on ATH. The coverage includes a brief background of the chemistry, TH and ATH reactions in water, and the mechanistic aspects of the aqueous-phase reduction.
Related Concept Videos
02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
02:13Reduction of Alkenes: Catalytic Hydrogenation
Metals like palladium, platinum, and nickel are commonly used in their solid forms — fine powder on an inert surface. As these catalysts remain insoluble in the reaction mixture, they are referred to as heterogeneous catalysts.
The hydrogenation process takes place on the surface of...
02:17Reduction of Alkenes: Asymmetric Catalytic Hydrogenation
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
01:21Acid-Catalyzed α-Halogenation of Aldehydes and Ketones
In the first step of the mechanism, the acid protonates the carbonyl oxygen resulting in a resonance-stabilized cation, which subsequently loses an α-hydrogen to form an enol tautomer. The C=C bond in an enol is highly nucleophilic because of the electron-donating nature of the –OH group. Consequently, the double bond attacks an electrophilic halogen to form a...
01:01Ketones with Nonenolizable Aromatic Aldehydes: Claisen–Schmidt Condensation
As the self-condensation of ketones is generally not favored in basic conditions, the self-condensed products do not form in the reaction between ketones and benzaldehyde. The general reaction of Claisen–Schmidt condensation is...