Mixture of poly(ethylene glycol) and water as environmentally friendly media for efficient enantioselective transfer hydrogenation and catalyst recycling

Poly(ethylene glycol) dimethyl ether mediated oxidative scission of aromatic olefins to carbonyl compounds by molecular oxygen

A simple, and practical oxidative scission of aromatic olefins to carbonyl compounds using O₂ as the sole oxidant with poly(ethylene glycol) dimethyl ether as a benign solvent has been developed. A wide range of monosubstituted, gem-disubstituted, 1,2-disubstituted, trisubstituted and tetrasubstituted aromatic olefins was successfully converted into the corresponding aldehydes and ketones in excellent yields even with gram–scale reaction. Some control experiments were also conducted to support a possible reaction pathway.

A simple and practical O₂ oxidized scission of monosubstituted, gem- and 1,2-disubstituted, trisubstituted and tetrasubstituted aromatic olefins to aldehydes and ketones in PEGDME has been developed.

Asymmetric transfer hydrogenation of cycloalkyl vinyl ketones to allylic alcohols catalyzed by ruthenium amido complexes

A chemoselective 1,2-reduction of cycloalkyl vinyl ketones via asymmetric transfer hydrogenation is described. The reduction proceeded smoothly with a chiral diamine ruthenium complex as a catalyst and a HCOOH-NEt3 azeotrope as both a hydrogen source and solvent under mild conditions. A wide range of 1-cycloalkyl chiral allylic alcohols were obtained in good yields and up to 87% ee. It was found that the alkyl group plays an important role in the enantioselectivity.

A new cost-effective Ru-chloramphenicol base derivative catalyst for the asymmetric transfer hydrogenation/dynamic kinetic resolution of N-Boc α-amino-β-ketoesters and its application to the synthesis of the chiral core of vancomycin

Herein we describe the application of Ru-chloramphenicol base complexes catalyzed highly diastereo- and enantioselective transfer hydrogenation of N-Boc α-amino-β-ketoesters for the asymmetric synthesis of anti-N-Boc-β-hydroxy-α-amino esters.

Fast reductive amination by transfer hydrogenation "on water"

Reductive amination of various ketones and aldehydes by transfer hydrogenation under aqueous conditions has been developed, by using cyclometallated iridium complexes as catalysts and formate as hydrogen source. The pH value of the solution is shown to be critical for a high catalytic chemoselectivity and activity, with the best pH value being 4.8. In comparison with that in organic solvents, the reductive amination in an aqueous phase is faster, and the molar ratio of the substrate to the catalyst (S/C) can be set as high as 1×10(5) , the highest S/C value ever reported in reductive amination reactions. The catalyst is easy to access and the reaction is operationally simple, allowing a wide range of ketones and aldehydes to react with various amines in high yields. The protocol provides a practical and environmental friendly new method for the synthesis of amine compounds.

Opportunities offered by chiral η⁶-arene/N-arylsulfonyl-diamine-RuII catalysts in the asymmetric transfer hydrogenation of ketones and imines

Methods for the asymmetric transfer hydrogenation (ATH) of ketones and imines are still being intensively studied and developed. Of foremost interest is the use of Noyori's [RuCl(η⁶-arene)(N-TsDPEN)] complexes in the presence of a hydrogen donor (i-PrOH, formic acid). These complexes have found numerous practical applications and have been extensively modified. The resulting derivatives have been heterogenized, used in ATH in water or ionic liquids and even some attempts have been made to approach the properties of biocatalysts. Therefore, an appropriate modification of the catalyst that suits the specific requirements for the reaction conditions is very often readily available. The mechanism of the reaction has also been explored to a great extent. Model substrates, acetophenone (a ketone) and 6,7-dimethoxy-1-methyl-3,4-dihydroisoquinoline (an imine), are both reduced by this Ru catalytic system with almost perfect selectivity. However, in each case the major product is a different enantiomer (S- for an alcohol, R- for an amine when the S,S-catalyst is used), which demanded an in-depth mechanistic investigation. Full-scale molecular modelling of this system enabled us to visualize the plausible 3D structures of the transition states, allowing the proposition of a viable explanation of previous experimental findings.

Asymmetric transfer hydrogenation of prochiral ketones catalyzed by aminosulfonamide-ruthenium complexes in ionic liquid

Chiral aminosulfonamides containing imidazolium group were used as ligands for the ruthenium(II)-catalyzed asymmetric transfer hydrogenation of prochiral ketones in ionic liquid, affording good to excellent conversions and enantiomeric excesses. The catalytic system could be easily recovered and reused several times.