Highly enantioselective reductive amination of simple aryl ketones catalyzed by Ir-f-Binaphane in the presence of titanium(IV) isopropoxide and iodine

An Iridium Catalytic System Compatible with Inorganic and Organic Nitrogen Sources for Dual Asymmetric Reductive Amination Reactions

Asymmetric reductive amination (ARA) is one of the most promising methods for the synthesis of chiral amines. Herein we report our efforts on merging two ARA reactions into a single-step transformation. Catalyzed by a complex formed from iridium and a steric hindered phosphoramidite, readily available and inexpensive aromatic ketones initially undergo the first ARA with ammonium acetate to afford primary amines, which serve as the amine sources for the second ARA, and finally provide the enantiopure C₂ -symmetric secondary amine products. The developed process competently enables the successive coupling of inorganic and organic nitrogen sources with ketones in the same reaction system. The Brønsted acid additive plays multiple roles in this procedure: it accelerates the formation of imine intermediates, minimizes the inhibitory effect of N-containing species on the iridium catalyst, and reduces the primary amine side products.

Chiral cyclometalated iridium complexes for asymmetric reduction reactions

A series of chiral cyclometalated iridium complexes have been synthesised by cyclometalating chiral 2-aryl-oxazoline and imidazoline ligands with [Cp*IrCl2]2. These iridacycles were studied for asymmetric transfer hydrogenation reactions with formic acid as the hydrogen source and were found to display various activities and enantioselectivities, with the most effective ones affording up to 63% ee in the asymmetric reductive amination of ketones and 77% ee in the reduction of pyridinium ions.

Enantioselective synthesis of tetrahydroisoquinolines via catalytic intramolecular asymmetric reductive amination

A highly efficient intramolecular asymmetric reductive amination transformation catalyzed by an iridium complex of ^tBu-ax-Josiphos has been realized, providing an efficient access to various THIQ alkaloids.

One-Pot Synthesis of Chiral N-Arylamines by Combining Biocatalytic Aminations with Buchwald-Hartwig N-Arylation

The combination of biocatalysis and chemo-catalysis increasingly offers chemists access to more diverse chemical architectures. Here, we describe the combination of a toolbox of chiral-amine-producing biocatalysts with a Buchwald-Hartwig cross-coupling reaction, affording a variety of α-chiral aniline derivatives. The use of a surfactant allowed reactions to be performed sequentially in the same flask, preventing the palladium catalyst from being inhibited by the high concentrations of ammonia, salts, or buffers present in the aqueous media in most cases. The methodology was further extended by combining with a dual-enzyme biocatalytic hydrogen-borrowing cascade in one pot to allow for the conversion of a racemic alcohol to a chiral aniline.

Transition-Metal-Catalyzed Reductive Amination Employing Hydrogen

The reductive amination, the reaction of an aldehyde or a ketone with ammonia or an amine in the presence of a reducing agent and often a catalyst, is an important amine synthesis and has been intensively investigated in academia and industry for a century. Besides aldehydes, ketones, or amines, starting materials have been used that can be converted into an aldehyde or ketone (for instance, carboxylic acids or organic carbonate or nitriles) or into an amine (for instance, a nitro compound) in the presence of the same reducing agent and catalyst. Mechanistically, the reaction starts with a condensation step during which the carbonyl compound reacts with ammonia or an amine, forming the corresponding imine followed by the reduction of the imine to the alkyl amine product. Many of these reduction steps require the presence of a catalyst to activate the reducing agent. The reductive amination is impressive with regard to the product scope since primary, secondary, and tertiary alkyl amines are accessible and hydrogen is the most attractive reducing agent, especially if large-scale product formation is an issue, since hydrogen is inexpensive and abundantly available. Alkyl amines are intensively produced and use fine and bulk chemicals. They are key functional groups in many pharmaceuticals, agro chemicals, or materials. In this review, we summarize the work published on reductive amination employing hydrogen as the reducing agent. No comprehensive review focusing on this subject has been published since 1948, albeit many interesting summaries dealing with one or the other aspect of reductive amination have appeared. Impressive progress in using catalysts based on earth-abundant metals, especially nanostructured heterogeneous catalysts, has been made during the early development of the field and in recent years.

Iridium-catalyzed enantioselective reductive amination of aromatic ketones

A highly efficient catalytic system of direct asymmetric reductive amination of aromatic ketones.

Catalysis, kinetics and mechanisms of organo-iridium enantioselective hydrogenation-reduction

The synthesis of chiral molecules is of great importance to the pharmaceutical, agrochemical, flavour and fragrance industries.

Secondary amines as coupling partners in direct catalytic asymmetric reductive amination

The secondary amine participating asymmetric reductive amination remains an unsolved problem in organic synthesis. Here we show for the first time that secondary amines are capable of effectively serving as N-sources in direct asymmetric reductive amination to afford corresponding tertiary chiral amines with the help of a selected additive set under mild conditions (0-25 °C). The applied chiral phosphoramidite ligands are readily prepared from BINOL and easily modified. Compared with common tertiary chiral amine synthetic methods, this procedure is much more concise and scalable, as exemplified by the facile synthesis of rivastigmine and N-methyl-1-phenylethanamine.

Direct Asymmetric Reductive Amination for the Synthesis of (S)-Rivastigmine

In this article we demonstrate how asymmetric total synthesis of (S)-rivastigmine has been achieved using direct asymmetric reductive amination as the key transformation in four steps. The route started with readily available and cheap m-hydroxyacetophenone, through esterification, asymmetric reductive amination, N-diphenylmethyl deprotection and reductive amination, to provide the final (S)-rivastigmine in 82% overall yield and 96% enantioselectivity. In the asymmetric reductive amination, catalysed by the iridium–phosphoramidite ligand complex and helped by some additives, the readily prepared 3-acetylphenyl ethyl(methyl)carbamate directly reductively coupled with diphenylmethanamine to yield the chiral amine product in 96% ee and 93% yield.

High-yielding continuous-flow synthesis of antimalarial drug hydroxychloroquine

Numerous synthetic methods for the continuous preparation of fine chemicals and active pharmaceutical ingredients (API’s) have been reported in recent years resulting in a dramatic improvement in process efficiencies. Herein we report a highly efficient continuous synthesis of the antimalarial drug hydroxychloroquine (HCQ). Key improvements in the new process include the elimination of protecting groups with an overall yield improvement of 52% over the current commercial process. The continuous process employs a combination of packed bed reactors with continuous stirred tank reactors for the direct conversion of the starting materials to the product. This high-yielding, multigram-scale continuous synthesis provides an opportunity to achieve increase global access to hydroxychloroquine for treatment of malaria.

A one-pot process for the enantioselective synthesis of tetrahydroquinolines and tetrahydroisoquinolines via asymmetric reductive amination (ARA)

Asymmetric reductive amination for the synthesis of both chiral tetrahydroquinolines and tetrahydroisoquinolines has been realized with an Ir/ZhaoPhos catalytic system via a one-pot N-Boc deprotection/intramolecular asymmetric reductive amination (ARA) sequence.

Facile synthesis of chiral indolines through asymmetric hydrogenation of in situ generated indoles

A concise synthesis of chiral indolines has been developed through intramolecular condensation, deprotection and palladium-catalyzed asymmetric hydrogenation in a one-pot process with up to 96% ee. A strong Brønsted acid played an important role in both the formation of indoles and asymmetric hydrogenation process.

Practical synthesis of enantiopure benzylamines by catalytic hydrogenation or transfer hydrogenation reactions in isopropanol using a Ru-pybox catalyst

A Ru/Ph-pybox catalyst provides a very high enantioselectivity in the hydrogenation and transfer hydrogenation of N-aryl imines.

Direct Catalytic Asymmetric Reductive Amination of Aliphatic Ketones Utilizing Diphenylmethanamine as Coupling Partner

The highly efficient direct catalytic reductive amination of ketones with diphenylmethanamine catalyzed by iridium-phosphoramidite complexes is described. As an effective coupling partner, diphenylmethanamine is suitable for a wide range of ketones to provide chiral amines in high yields and enantioselectivity. The chiral monodentate phosphoramidite ligands are tunable and competent to accommodate substrates with different structures.

CuI nanoparticles as recyclable heterogeneous catalysts for C–N bond formation reactions

Herein, copper iodide nanoparticles (NPs) are reported for the reductive amination of carbonyl compounds for the first time.

Iridium-catalyzed direct asymmetric reductive amination of aromatic ketones

Diphenylmethanamine offers excellent stereocontrol and easy deprotection to provide primary amines in the studied asymmetric reductive amination.