Iridium-catalyzed direct asymmetric reductive amination utilizing primary alkyl amines as the N-sources

Direct asymmetric reductive amination is one of the most efficient methods for the construction of chiral amines, in which the scope of the applicable amine coupling partners remains a significant challenge. In this study we describe primary alkyl amines effectively serve as the N-sources in direct asymmetric reductive amination catalyzed by the iridium precursor and sterically tunable chiral phosphoramidite ligands. The density functional theory studies of the reaction mechanism imply the alkyl amine substrates serve as a ligand of iridium strengthened by a (N)H-O(P) hydrogen-bonding attraction, and the hydride addition occurs via an outer-sphere transition state, in which the Cl-H H-bonding plays an important role. Through this concise procedure, cinacalcet, tecalcet, fendiline and many other related chiral amines have been synthesized in one single step with high yields and excellent enantioselectivity.

Direct asymmetric reductive amination is one of the most efficient methods for obtaining chiral amines. Here the authors show how primary alkyl amines can undergo this transformation in the presence of an iridium catalyst with sterically tuneable chiral phosphoramidite ligands, achieving the synthesis of pharmaceutical compounds.

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.

Highly Enantioselective Direct Asymmetric Reductive Amination of 2-Acetyl-6-Substituted Pyridines

A highly direct asymmetric reductive amination of a variety of ketone substrates, including 2-acetyl-6-substituted pyridines, β-keto esters, β-keto amides, and 1-(6-methylpyridin-2-yl)propan-2-one, has been disclosed for the first time (94.6% to >99.9% ee). With ammonium trifluoroacetate as the nitrogen source, various chiral corresponding primary amines were prepared in excellent enantioselectivity and conversion in the presence of a commercially available and inexpensive chiral catalyst, Ru(OAc)₂{(S)-binap}, under 0.8 MPa of hydrogen gas pressure.

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.

Recent advances on transition-metal-catalysed asymmetric reductive amination

This review focuses on the recent progress of homogeneous transition-metal-catalysed asymmetric reductive amination of ketones with diverse nitrogen sources.

Iridium-catalyzed enantioselective reductive amination of aromatic ketones

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

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.

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.

Synthesis of chiral sultams with two adjacent stereocenters via palladium-catalyzed dynamic kinetic resolution

A palladium-catalyzed intramolecular asymmetric reductive amination of racemic α-branched ketones bearing the poorly nucleophilic sulfonamides has been successfully developed through dynamic kinetic resolution, providing chiral δ-sultams with two contiguous stereogenic centers.