Iridium Ferrocenyl Diphosphine Catalyzed Enantioselective Reductive Alkylation of a Hindered Aniline

Diastereo- and enantioselective reductive amination of cycloaliphatic ketones by preformed chiral palladium complexes

Chiral cycloaliphatic amines were obtained from the direct asymmetric reductive amination of cycloaliphatic ketones using a preformed chiral palladium catalyst.

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.

Asymmetric reductive amination

Asymmetric reductive amination (ARA) affords synthetically valuable chiral amines straightforwardly. This chapter reviews the recent advances made in the area, focusing on ARA by hydrogenation, transfer hydrogenation, organocatalytic reduction, and biocatalytic reduction.

Reaction development and mechanistic study of a ruthenium catalyzed intramolecular asymmetric reductive amination en route to the dual Orexin inhibitor Suvorexant (MK-4305)

The first example of an intramolecular asymmetric reductive amination of a dialkyl ketone with an aliphatic amine has been developed for the synthesis of Suvorexant (MK-4305), a potent dual Orexin antagonist under development for the treatment of sleep disorders. This challenging transformation is mediated by a novel Ru-based transfer hydrogenation catalyst that provides the desired diazepane ring in 97% yield and 94.5% ee. Mechanistic studies have revealed that CO(2), produced as a necessary byproduct of this transfer hydrogenation reaction, has pronounced effects on the efficiency of the Ru catalyst, the form of the amine product, and the kinetics of the transformation. A simple kinetic model explains how product inhibition by CO(2) leads to overall first-order kinetics, but yields an apparent zero-order dependence on initial substrate concentration. The deleterious effects of CO(2) on reaction rates and product isolation can be overcome by purging CO(2) from the system. Moreover, the rate of ketone hydrogenation can be greatly accelerated by purging of CO(2) or trapping with nucleophilic secondary amines.

Bifunctional catalysis: direct reductive amination of aliphatic ketones with an iridium-phosphate catalyst

Chiral amines are one of the ubiquitous functional groups in fine chemical, pharmaceutical and agrochemical products, and the most convenient, economical, and eco-benign synthetic pathway to these amines is direct asymmetric reductive amination (DARA) of prochiral ketones. This paper shows that a wide range of aliphatic ketones can be directly aminated under hydrogenation conditions, affording chiral amines with good to excellent yields and with enantioselectivities up to 96% ee. The catalysis is effected by the cooperative action of a cationic Cp*Ir(III) complex and its phosphate counteranion.

Platinum-Catalyzed Intramolecular Asymmetric Hydroarylation of Unactivated Alkenes with Indoles

[reaction: see text] A 1:1 mixture of the platinum bis(phosphine) complex [(S)-4]PtCl2 [(S)-4 = (S)-3,5-t-Bu-4-MeO-MeOBIPHEP] catalyzes the intramolecular asymmetric hydroarylation of 2-(4-pentenyl)indoles in moderate to good yield with up to 90% ee.

Hydrogen Bond Catalyzed Direct Reductive Amination of Ketones

[reaction: see text] A novel, biomimetic concept for the direct reductive amination of ketones is described that relies on selective imine activation by hydrogen bond formation. The mild, acid- and metal-free process requires only catalytic amounts of thiourea as hydrogen bond donor and utilizes the Hantzsch ester for transfer hydrogenation. The method allows the efficient synthesis of structurally diverse amines.

Enantioselective Organocatalytic Reductive Amination

The first enantioselective organocatalytic reductive amination reaction has been accomplished. The development of a new chiral phosphoric acid catalyst has provided a convenient strategy for the enantioselective construction of protected primary amines and provided a highly stereoselective method for the reductive amination of heterocyclic amines. A diverse spectrum of ketone and amine substrates can be accommodated in high yield and excellent enantioselectivity. This new protocol realizes a key benefit of reductive amination versus imine reduction, in that ketimines derived from alkyl-alkyl ketones are unstable to isolation, a fundamental limitation that is comprehensively bypassed using this direct organocatalytic reductive amination.

Synthesis of primary amines: first homogeneously catalyzed reductive amination with ammonia

[reaction: see text] The synthesis of primary amines via reductive amination of the corresponding carbonyl compounds with aqueous ammonia is achieved for the first time with soluble transition metal complexes. Up to an 86% yield and a 97% selectivity for benzylamines were obtained in the case of various benzaldehydes by using a Rh-catalyst together with water-soluble phosphine and ammonium acetate. In the case of aliphatic aldehydes, a bimetallic catalyst based on Rh/Ir gave improved results.

Halide effects in transition metal catalysis

Among the most common ligands found on transition metal catalysts are halide ions. Of the commercially available catalysts or pre-catalysts, most are halo-metal complexes. In recent years, manipulation of this metal-halide functionality has revealed that this can be used as a highly valuable method of tuning the reactivity of the complex. Variation of the halide ligand will usually not alter the nature of the system to the extent that it becomes unreactive but will impart sufficiently large changes that differences in reactivity or selectivity occur. These differences are a product of the steric and electronic properties of the halide ligand which has the ability to donate electron density to the metal occurs in a predictable manner. Despite the common perception in asymmetric catalysis that halide ligands are of secondary importance compared to chiral ligands, halide ligands have been found to exert dramatic effects on the enantioselectivity of asymmetric transformations. While the mechanism of action is known for relatively few of the cases, many intriguing and potentially synthetically useful trends are apparent. This review discusses the physical properties of the halides and their effects on stoichiometric and catalytic transition metal processes. The metal-halide moiety thus emerges as a tunable functionality on the transition metal catalyst that can be used in the development of new catalytic systems.