Enantioselective Transfer Hydrogenation of α-Methoxyimino-β-keto Esters

α-Methoxyimino-β-keto esters are reported to undergo highly enantioselective catalytic transfer hydrogenation using the Noyori-Ikariya complex RuCl(p-cymene)[(S,S)-Ts-DPEN] in a mixture of formic acid-triethylamine and dimethylformamide at 25 °C. The experimental study performed on over 25 substrates combined with computational analysis revealed that a Z-configured methoxyimino group positioned alpha to a ketone carbonyl leads to higher reactivity and mostly excellent enantioselectivity within this substrate class. Density functional theory calculations of competing transition states were used in rationalizing the origins of enantioselectivity and the possible role of the methoxyimino group in the reaction outcome.

Synthesis of MeBmt and related derivatives via syn-selective ATH-DKR

The unusual α-amino, β-hydroxy acid MeBmt is a key structural feature of cyclosporin A, an important naturally occurring immunosuppressant and antiviral agent. We present a convergent synthesis of MeBmt which relies on new aspects of dynamic kinetic resolution (DKR) to establish simultaneously the chirality at C(2) and C(3). We also show that this route is applicable to the synthesis of other derivatives.

Rhodium-mediated asymmetric transfer hydrogenation: a diastereo- and enantioselective synthesis of syn-α-amido β-hydroxy esters

The use of a Rh- instead of a Ru-complex in the asymmetric transfer hydrogenation of α-benzoylamino β-keto esters allowed a reversal of diastereoselectivity and an efficient access to a variety of syn α-amido β-hydroxy esters.

Enantioselective Synthesis of α-Acetal-β'-Amino Ketone Derivatives by Rhodium-Catalyzed Asymmetric Hydrogenation

A range of β-keto-γ-acetal enamides has been synthesized and transformed into the corresponding enantioenriched α-acetal-β'-amino ketones with enantioinductions of up to 99% by using rhodium/QuinoxP*-catalyzed enantioselective hydrogenation under mild conditions. This method also proved to be highly chemoselective toward the reduction of the C-C double bond.

Rhodium-catalyzed asymmetric hydrogenation of tetrasubstituted β-acetoxy-α-enamido esters and efficient synthesis of droxidopa

Rhodium-catalyzed asymmetric hydrogenation of challenging tetrasubstituted β-acetoxy-α-enamido esters was developed, giving chiral β-acetoxy-α-amido esters in high yields with excellent enantioselectivities. This protocol provides an efficient route for the synthesis of droxidopa.

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.

γ-Sultam-cored N,N-ligands in the ruthenium(ii)-catalyzed asymmetric transfer hydrogenation of aryl ketones

Excellent enantioselectivities were obtained in the asymmetric transfer hydrogenation of benzo-fused ketones employing Ru(ii)-[syn-6]; dynamic kinetic resolution of rac-S7 was realized.