Asymmetric Hydrogenation Research Articles

Enantio- and Diastereoselective Total Synthesis of Belzutifan Enabled by Rh-Catalyzed Hydrogenation.

Herein, we report a nine-step synthesis of belzutifan enabled by a novel Rh-catalyzed asymmetric hydrogenation to install the contiguous fluorinated stereocenters with high enantioselectivity. Moreover, the final ketone reduction in the synthesis proceeds with high diastereoselectivity, leading to the expedient assembly of the stereotriad. In contrast to the original 16-step synthesis, this route avoids a lengthy bromination-oxidation sequence and introduces the sulfone functionality via nucleophilic aromatic substitution, obviating the need for transition metal catalysis.

RuPHOX-Ru Catalyzed Asymmetric Cascade Hydrogenation of 3-Substituted Chromones for the Synthesis of Corresponding Chiral Chromanols​.

An efficient RuPHOX-Ru catalyzed asymmetric cascade hydrogenation of 3-substituted chromones has been achieved under mild reaction conditions, affording the corresponding chiral 3-substituted chromanols in high yields with excellent enantio- and diastereoselectivities (up to 99% yield, >99% ee and >20:1 dr). Control reactions and deuterium labelling experiments revealed that a dynamic kinetic resolution process occurs during the subsequent hydrogenation of the C=O double bond, which is responsible for the high performance of the asymmetric cascade hydrogenation. The resulting products allow for several transformations and it was shown that the protocol provides a practical and alternative strategy for the synthesis of chiral 3-substituted chromanols and their derivatives.

Synthesis and crystal structure of (NH4)[Ni3(HAsO4)(AsO4)(OH)2]

The title compound, ammonium trinickel(II) hydrogen arsenate arsenate dihydroxide, was synthesized under hydrothermal conditions. Its crystal structure is isotypic with that of K[Cu3(HAsO4)(AsO4)(OH)2] and is characterized by pseudo-hexagonal (001) 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]− layers formed from vertex- and edge-sharing [NiO4(OH)2] octahedra and [AsO3.5(OH)0.5] tetrahedra as the building units. The hydrogen atom of the OH group shows occupational disorder and was refined with a site occupation factor of 1/2, indicating the equal presence of [HAsO4]2– and [AsO4]3– groups. Strong asymmetric hydrogen bonds between symmetry-related (O,OH) groups of the arsenate units [O...O = 2.588 (18) Å] as well as hydrogen bonds accepted by these (O,OH) groups from OH groups bonded to the NiII atoms [O...O = 2.848 (12) Å] link adjacent layers. Additional consolidation of the packing is achieved through N—H...O hydrogen bonds from the ammonium ion, which is sandwiched between adjacent layers [N...O = 2.930 (7) Å] although the H atoms could not be located in the present study. The presence of the pseudo-hexagonal 2 ∞[Ni3As2O18/3(OH)6/3O1/1(OH)1/1]− layers may be the reason for the systematic threefold twinning of (NH4)[Ni3(HAsO4)(AsO4)(OH)2] crystals. Significant overlaps of the reflections of the respective twin domains complicated the structure solution and refinement.

Three‐Component Palladium‐Catalyzed Tandem Suzuki‐Miyaura/Allylic Substitution: A Regioselective Synthesis of (2‐Arylallyl) Aryl Sulfones

A one‐pot Pd‐catalyzed tandem process to prepare (2‐arylallyl) aryl sulfones has been developed. This strategy is based on the modular assembly of a boronic acid, a sodium sulfinate and 2‐bromoallyl acetate. The reaction is completely regioselective towards the terminal alkene, yielding (2‐arylallyl) aryl (or alkyl) sulfones with yields ranging from 56 to 93%. Control experiments together with DFT calculations allowed to propose a plausible reaction mechanism of the tandem reaction. The usefulness of this methodology has been demonstrated with the formal synthesis of the marketed drug Apremilast and of several natural products by asymmetric hydrogenation. Using the commercially available UbaPHOX iridium complex, chiral β‐methyl sulfones with up to 98% ee were obtained

Synthesis of Chiral 1,2-Amino Alcohol-Containing Compounds Utilizing Ruthenium-Catalyzed Asymmetric Transfer Hydrogenation of Unprotected α-Ketoamines.

Herein, we disclose a facile synthetic strategy to access an important class of drug molecules that contain chiral 1,2-amino alcohol functionality utilizing highly effective ruthenium-catalyzed asymmetric transfer hydrogenation of unprotected α-ketoamines. Recently, the COVID-19 pandemic has caused a crisis of shortage of many important drugs, especially norepinephrine and epinephrine, for the treatment of anaphylaxis and hypotension because of the increased demand. Unfortunately, the existing technologies are not fulfilling the worldwide requirement due to the existing lengthy synthetic protocols that require additional protection and deprotection steps. We identified a facile synthetic protocol via a highly enantioselective one-step process for epinephrine and a two-step process for norepinephrine starting from unprotected α-ketoamines 1b and 1a, respectively. This newly developed enantioselective ruthenium-catalyzed asymmetric transfer hydrogenation was extended to the synthesis of many 1,2-amino alcohol-containing drug molecules such as phenylephrine, denopamine, norbudrine, and levisoprenaline, with enantioselectivities of >99% ee and high isolated yields.

Polarizability matters in enantio-selection

The prevalence of chirality, or, handedness in biological world is a fundamental phenomenon and a characteristic hallmark of life. Thus, understanding the origin of enantio-selection, i.e., the sense and magnitude of asymmetric induction, has been a long-pursued goal in asymmetric catalysis. Herein, we demonstrated a polarizability-derived electronic effect that was shown to be capable of rationalizing a broad range of stereochemical observations made in the field of asymmetric catalysis. This effect provided a consistent enantio-control model for the prediction of major enantiomers formed in a ruthenium-catalyzed asymmetric transfer hydrogenations of ketones. Direct and quantitative linear free energy relationships between substrates’ local polarizabilities and observed enantio-selectivity were also revealed in three widely known asymmetric catalytic systems covering both reductions and oxidations. This broadly applicable polarizability-based electronic effect, in conjunction with conventional wisdom mainly leveraging on steric effect considerations, should aid rational design of enantio-selective processes for better production of chiral substances.

Cyclometallated Imides as Templates for the H-Bond Directed Iridium-Catalyzed Asymmetric Hydrogenation of N-Methyl, N-Alkyl and N-Aryl Imines.

A combined computational and experimental approach allowed us to develop the most selective catalysts for the direct hydrogenation of N-methyl and N-alkyl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99% enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H-bonding of the imide C=O with the substrate iminium ion and a stabilizing π-π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H-bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air-stable solid. X-ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H-bond with the substrate. 19F-NMR real-time monitoring showed the hydrogenation of N-methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h-1.

Cyclometallated Imides as Templates for the H‐Bond Directed Iridium‐Catalyzed Asymmetric Hydrogenation of N‐Methyl, N‐Alkyl and N‐Aryl Imines

Cyclometallated Imides as Templates for the H‐Bond Directed Iridium‐Catalyzed Asymmetric Hydrogenation of N‐Methyl, N‐Alkyl and N‐Aryl Imines

Selective Hydrofunctionalization of Alkenyl Fluorides Enabled by Nickel-Catalyzed Hydrogen Atoms and Group Transfer: Reaction Development and Mechanistic Study.

Due to the unique effect of fluorine atoms, the efficient construction of high-value alkyl fluorides has attracted significant interest in modern drug development. However, enantioselective catalytic strategies for the efficient assembly of highly functionalized chiral C(sp3)-F scaffolds from simple starting materials have been underutilized. Herein, we demonstrate a nickel-catalyzed radical transfer strategy for the efficient, modular, asymmetric hydrogenation and hydroalkylation of alkenyl fluorides with primary, secondary, and tertiary alkyl halides under mild conditions. The transformation provides facile access to various structurally complex secondary and tertiary α-fluoro amide products from readily available starting materials with excellent substrate compatibility and distinct selectivity. Furthermore, the utility of this method is demonstrated by late-stage modifications and product derivatizations. Detailed mechanistic studies and DFT calculations have been conducted, showing that the rate-determining step for asymmetric hydrogenation reaction is NiH-HAT toward alkenyl fluorides and the stereo-determining step is alcohol coordination to Ni-enolates followed by a barrierless protonation. The mechanism for the asymmetric hydroalkylation reaction is also delivered in this investigation.

Chiral P,N,N‐Ligands for Asymmetric Hydrogenation

The chiral P,N,N‐ligands represented a new type of tridentate ligand developed in recent years and displayed wide utilities in asymmetric catalysis. In the past decades, numerous chiral P,N,N‐ligands with ferrocene, phenethylamine and spiro backbones were synthesized by addition of an aminopyridine, imidazole or diamines coordinating group. These chiral tridentate P,N,N‐ligands showed excellent performance in the ruthenium, iridium, manganese, or cobalt‐catalyzed asymmetric hydrogenations. A wide range of substrates, including simple ketones, α‐halogenated ketones, α‐hydroxy ketones, α‐ or β‐amino ketones, α‐, γ‐, or δ‐keto acids, α‐ or β‐keto amides, β‐ or δ‐keto esters, α‐ or β‐enones, olefins, imines, quinolines and indoles, could be hydrogenated to afford the corresponding chiral products with high yields and enantioselectivities. In this review, progress on the asymmetric hydrogenation of C=O, C=N, C=C bonds with chiral tridentate P,N,N‐ligands was summarized.

α-Alkylation and Asymmetric Transfer Hydrogenation of Tetralone via Hydrogen Borrowing and Dynamic Kinetic Resolution Strategy Using a Single Iridium(III) Complex.

Here we present a novel strategy for the synthesis of enantiomerically enriched tetrahydronaphthalen-1-ols. The reaction proceeds via an alkylation (via hydrogen borrowing) and ammonium formate-mediated asymmetric transfer hydrogenation (via dynamic kinetic resolution), giving alkylated tetralols in high yields and good enantio- and diastereoselectivity across a diverse range of both alcohol and tetralone substrates. Additionally, these products were successfully derivatized to several complex molecules, demonstrating the utility of the tetrahydronaphthalen-1-ol.

Asymmetric Hydrogenative Coupling of Indoles with Unsaturated Ketones Enabled by Copper/Ruthenium Relay Catalysis

AbstractA relay catalytic system is developed for the asymmetric hydrogenative coupling of indoles with α,β-unsaturated ketones, affording enantioenriched chiral γ-indole alcohols with broad substrate scope and excellent enantioselectivities (32 examples, up to >99% ee). Mechanistic studies suggest that the relay catalytic system consists of copper-catalyzed alkylation and ruthenium-catalyzed asymmetric hydrogenation.

Achieving Strong Circularly Polarized Luminescence through Cascade Cationic Insertion in Lead-free Hybrid Metal Halides.

Generating circularly polarized luminescence (CPL) with simultaneous high photoluminescence quantum yield (PLQY) and dissymmetry factor (glum) is difficult due to usually unmatched electric transition dipole moment (µ) and magnetic transition dipole moment (m) of materials. Herein we tackle this issue by playing a "cascade cationic insertion" trick to achieve strong CPL (with PLQY of ~ 100%) in lead-free metal halides with high glum values reaching -2.3×10-2 without using any chiral inducers. Achiral solvents of hydrochloric acid (HCl) and N, N-dimethylformamide (DMF) infiltrate the crystal lattice via asymmetric hydrogen bonding, distorting the perovskite structure to induce the "intrinsic" chirality. Surprisingly, additional insertion of Cs+ cation to substitute partial (CH3)2NH2+ transforms the chiral space group to achiral but the crystal maintains chiroptical activity. Further doping of Sb3+ stimulates strong photoluminescence as a result of self-trapped excitons (STEs) formation without disturbing the crystal framework. The chiral perovskites of indium-antimony chlorides embedded on LEDs chips demonstrate promising potential as CPL emitters. Our work presents rare cases of chiroptical activity of highly luminescent perovskites from only achiral building blocks via spontaneous resolution as a result of symmetry breaking.

Achieving Strong Circularly Polarized Luminescence through Cascade Cationic Insertion in Lead‐free Hybrid Metal Halides

Generating circularly polarized luminescence (CPL) with simultaneous high photoluminescence quantum yield (PLQY) and dissymmetry factor (glum) is difficult due to usually unmatched electric transition dipole moment (µ) and magnetic transition dipole moment (m) of materials. Herein we tackle this issue by playing a “cascade cationic insertion” trick to achieve strong CPL (with PLQY of ~ 100%) in lead‐free metal halides with high glum values reaching ‐2.3×10‐2 without using any chiral inducers. Achiral solvents of hydrochloric acid (HCl) and N, N‐dimethylformamide (DMF) infiltrate the crystal lattice via asymmetric hydrogen bonding, distorting the perovskite structure to induce the “intrinsic” chirality. Surprisingly, additional insertion of Cs+ cation to substitute partial (CH3)2NH2+ transforms the chiral space group to achiral but the crystal maintains chiroptical activity. Further doping of Sb3+ stimulates strong photoluminescence as a result of self‐trapped excitons (STEs) formation without disturbing the crystal framework. The chiral perovskites of indium‐antimony chlorides embedded on LEDs chips demonstrate promising potential as CPL emitters. Our work presents rare cases of chiroptical activity of highly luminescent perovskites from only achiral building blocks via spontaneous resolution as a result of symmetry breaking.

Organometallic Mn(I) Complexes in Asymmetric Catalytic (Transfer) Hydrogenation and Related Transformations

AbstractDirect asymmetric hydrogenation (AH) and asymmetric transfer hydrogenation (ATH) are among the most efficient approaches to produce chiral building blocks. Recently, these types of transformations have witnessed a shift towards the use of molecular catalysts based on earth‐abundant transition metals due to their ready availability, economic advantage, and novel properties. With particular regard to manganese, catalyst development has seen both the efficiency and substrate scope in AH and ATH greatly improved, with the emergence of a large number of well‐defined Mn‐complexes employed in this field. The reaction scope includes the AH and ATH of C=O bonds, asymmetric reduction of C=N bonds and the asymmetric reductive transformations of C=C bonds. Herein, our survey of the area focuses on the catalytic activity of such complexes, their versatility towards asymmetric transformations and the routes employed to convert substrates to their target molecules. We consider the collected findings of this article will be helpful to the reader by providing an insight into ligand design, thereby aiding future catalyst development. Moreover, this review is aimed at highlighting the remarkable progress made in the last seven years in the development of manganese complexes for enantioselective reduction.

Bimetallic Ru/Ru-Catalyzed Asymmetric One-Pot Sequential Hydrogenations for the Stereodivergent Synthesis of Chiral Lactones.

Asymmetric sequential hydrogenations of α-methylene γ- or δ-keto carboxylic acids are established in one-pot using a bimetallic Ru/Ru catalyst system, achieving the stereodivergent synthesis of all four stereoisomers of both chiral γ- and δ-lactones with two non-vicinal carbon stereocenters in high yields (up to 99%) and with excellent stereoselectivities (up to >99% ee and >20:1 dr). The compatibility of the two chiral Ru catalyst systems is investigated in detail, and it is found that the basicity of the reaction system plays a key role in the sequential hydrogenation processes. The protocol can be performed on a gram-scale with a low catalyst loading (up to 11000 S/C) and the resulting products allow for many transformations, particularly for the synthesis of several key intermediates useful for the preparation of chiral drugs and natural products.

Asymmetric Hydrogenation of Acrylates by COF with Chiral Frustrated Lewis Pairs

Asymmetric Hydrogenation of Acrylates by COF with Chiral Frustrated Lewis Pairs

Iridium-Catalyzed Asymmetric Hydrogenation of Heteroaromatics with Multiple N Atoms via Substrate Activation: An Entry to 4,5,6,7-Tetrahydropyrazolo[1,5-a]pyrimidine-3-carbonitrile Core of a Potent BTK Inhibitor.

The chiral 4,5,6,7-tetrahydropyrazolo[1,5-a]pyrimidine is the key core skeleton of potent Bruton's tyrosine kinase (BTK) inhibitor Zanubrutinib, and the catalyst-controlled asymmetric hydrogenation of planar multinuclear pyrimidine heteroarenes with multiple N atoms could provide an efficient route toward its synthesis. Owing to the strong aromaticity and poisoning effect toward chiral transition metal catalyst, asymmetric hydrogenation of pyrazolo[1,5-a]pyrimidines with multiple nitrogen atoms is still a challenge for synthesizing the chiral 4,5,6,7-tetrahydropyrazolo[1,5-a]-pyrimidine. Herein, an efficient iridium-catalyzed asymmetric hydrogenation of pyrazolo[1,5-a]pyrimidines has been developed using substrate activation strategy, with up to 99% ee. The decagram scale synthesis further demonstrated the potential and promise of this procedure in the synthesis of Zanubrutinib. In addition, a mechanistic study indicated that the hydrogenation starts with 1,2-hydrogenation.

Spiro-Josiphos Ligands for the Ir-Catalyzed Asymmetric Synthesis of Chiral Amines under Hydrogenation Conditions.

Transition metal-catalyzed asymmetric hydrogenation possesses unparalleled advantages to prepare chiral amines. Here we reported a novel ligand that combined Josiphos and a spirobiindane scaffold and simultaneously investigated its application in Ir-catalyzed asymmetric hydrogenation for the synthesis of chiral amines. Excellent catalytic activity (5000 TON), high enantioselectivity (up to 99% ee), and broad substrate scope (different C═N substrates) make it highly promising for both academic research and industrial applications.

Efficient and Scalable Enantioselective Synthesis of a Key Intermediate for Rimegepant: An Oral CGRP Receptor Antagonist

Rimegepant is a calcitonin gene-related peptide antagonist used for acute treatment and prevention of migraine. We herein attempt to explore an efficient and practiced method for scale-up, regio- and enantioselective synthesis of (R)-9-hydroxy-6,7,8,9-tetrahydro-5H-cyclohepta[b]pyridin-5-one (1), a key intermediate of rimegepant. In this work, a Ru-catalyzed asymmetric transfer hydrogenation (ATH) reaction was a key step. The optimization of the reaction conditions involved exploring the reaction parameters including catalysts, bases, and solvents. The results suggested that the Ru-catalyzed ATH process using formic acid as the hydrogen donor could be operated under mild conditions at a low catalyst loading (0.5 mol%), affording a high yield (92.1% yield with 99.8% purity) and gratifying enantioselectivity (99.9% ee) of the target product (1). This work first reported the Ru-catalyzed ATH process in the synthesis of key intermediates of rimegepant. The optimized ATH process was easy to implement and cost-effective, making it particularly suitable for manufacturing scale production.