Catalytic Enantioselective Synthesis of α-Chiral Azaheteroaryl Ethylamines by Asymmetric Protonation

Copper(I)-Catalyzed Asymmetric 1,4-Hydroarsination of α,β-Unsaturated Compounds

Herein, a copper(I)-catalyzed asymmetric 1,4-hydroarsination of β-substituted α,β-unsaturated esters is achieved in moderate to excellent yields with high to excellent enantioselectivity, based on the proposed nucleophilic [Cu]-AsPh2 species. As for α-substituted α,β-unsaturated esters, a 1,4-hydroarsination/enantioselective protonation event occurs smoothly in satisfying results. Furthermore, β-substituted α,β-unsaturated ketone, α,β-unsaturated amide, and α,β-unsaturated phosphine sulfide are well applied in the present catalytic system. Finally, some control experiments show that HAsPh2 is activated through coordination with the copper(I) catalyst and HAsPh2 exhibits inferior soft Lewis basicity to HPPh2 in the presence of a copper(I)-bisphosphine complex.

Electrochemical sulfonylation/Truce-Smiles rearrangement of N-allylbenzamides: toward sulfone-containing β-arylethylamines and Saclofen analogues

The β-arylethylamine pharmacophore is commonly found in medications for central nervous system disorders, prompting the need for safe and efficient methods to endow this motif with relevant functional groups for drug discovery. In this context, herein, we have established electrochemical radical sulfonylation reactions of N-allylbenzamides followed by Truce-Smiles rearrangement to produce sulfone- and sulfonate ester-containing β-arylethylamines. Electricity enables this transformation to occur under mild and oxidant-free conditions. Simple sources of sulfonyl radicals and SO2 surrogates were employed to form sulfones and sulfonate esters, respectively. This practical and operationally robust method exhibited a broad substrate scope with good to high yields. The prospective pharmaceutical utility of the process was further demonstrated by removing the N-protecting groups and hydrolysing the sulfonate ester moiety to provide γ-sulfonyl-β-arylamines and Saclofen.

Catalytic Asymmetric Hydrogen Atom Transfer Based on a Chiral Hydrogen Atom Donor Generated from TBADT and Chiral BINOL

Enantioselective radical reactions mediated by TBADT have seldom been seen due to the inherent challenges. Herein, we disclose a new chiral hydrogen atom transfer (HAT) reagent that was generated easily from 8H-BINOL, potassium carbonate, and TBADT under irradiation. The new complex 8H-BINOL/DTs could be used as a chiral H donor. A series of azaarenes could be converted into the corresponding chiral compounds via radical addition followed by enantioselective HAT.

Chiral phosphoric acid-catalyzed asymmetric epoxidation of alkenyl aza-heteroarenes using hydrogen peroxide

The synthesis of chiral α-azaheteroaryl oxiranes via enantioselective catalysis is a formidable challenge due to the required complex stereoselectivity and diverse N-heterocyclic structures. These compounds play a crucial role in developing bioactive molecules, where precise chirality significantly influences biological activity. Here we show that using chiral phosphoric acid as a catalyst, our method efficiently addresses these challenges. This technique not only achieves high enantio- and diastereoselectivity but also demonstrates superior chemo- and stereocontrol during the epoxidation of alkenyl aza-heteroarenes. Our approach leverages a synergistic blend of electrostatic and hydrogen-bonding interactions, enabling the effective activation of both substrates and hydrogen peroxide. The resulting chiral oxiranes exhibit enhanced diversity and functionality, aiding the construction of complex chiral azaaryl compounds with contiguous stereocenters. Kinetic and density functional theory studies elucidate the mechanism, highlighting chiral phosphoric acid's pivotal role in this intricate enantioselective process.

Metal Free Functionalization of Saturated Heterocycles with Vinylarenes and Pyridine Enabled by Photocatalytic Hydrogen Atom Transfer

Saturated heterocycles are important class of structural scaffolds in small-molecule drugs, natural products, and synthetic intermediates. Here, we disclosed a metal free, mild, and scalable functionalization of saturated heterocycles using vinylarenes as a linchpin approach. Key to success of this transformation is the employing of simple and cheap benzophenone as a hydrogen atom transfer (HAT) catalyst. This operationally robust process was used for the making of diverse functionalized saturated heterocycles. Furthermore, aldehydes, alkane, and alcohol have been functionalized under the optimized conditions. The potential pharmaceutical utility of the procedure has also been demonstrated by late-stage functionalization of bioactive natural compounds and pharmaceutical molecules. Initial mechanism studies and control experiments were performed to elucidate the mechanism of the reactions.

Accessing Rare α-Heterocyclic Aziridines via Brønsted Acid-catalyzed Michael Addition/Annulation: Scope, Limitations, and Mechanism

We report an approach to the diastereoselective synthesis of 1,2-disubstituted heterocyclic aziridines. A Brønsted acid-catalyzed conjugate addition of anilines to trisubstituted heterocyclic chloroalkenes provides an intermediate 1,2-chloroamine. Diastereocontrol was found to vary significantly with solvent selection, with computational modelling confirming selective, spontaneous fragmentation in the presence of trace acids, proceeding through a pseudo-cyclic, protonated intermediate and transition state. These chloroamines can then be converted to the aziridine by treatment with LiHMDS with high stereochemical fidelity. This solvent-induced stereochemical enrichment thereby enables an efficient route to rare cis-aziridines with high dr. The scope, limitations, and mechanistic origins of selectivity are also presented.

Catalyst-free anti-Markovnikov hydroamination and hydrothiolation of vinyl heteroarenes in aqueous medium: an improved process towards centhaquine

Catalyst-free hydroamination and hydrothiolation of alkenes have been achieved in an aqueous medium. The anti-Markovnikov addition works efficiently in suspended water at room temperature and allows straightforward access to centhaquine, a drug used for the management of hypovolemic shocks in critically ill patients, and its derivatives. Various primary and secondary amines, thiols, and hydrazides were successfully reacted with a number of heteroaryl/aryl-alkenes. The scalability of the process has been demonstrated by synthesizing centhaquine at a 19.65 g scale. A comparative analysis of the present process with previous approaches has been provided on the basis of green chemistry metrics.

Enantioselective Hydrophosphination of Terminal Alkenyl Aza-Heteroarenes

This paper presents a Mn(I)-catalysed methodology for the enantioselective hydrophosphination of terminal alkenyl aza-heteroarenes. The catalyst operates through H-P bond activation, enabling successful hydrophosphination of a diverse range of alkenyl-heteroarenes with high enantioselectivity. The presented protocol addresses the inherently low reactivity and the commonly encountered suboptimal enantioselectivities of these challenging substrates. As an important application we show that this method facilitates the synthesis of a non-symmetric tridentate P,N,P-containing ligand like structure in just two synthetic steps using a single catalytic system.

Nickel-Catalyzed Three-Component Alkylarylation of Alkenyl N-Heteroarenes

A nickel-catalyzed three-component alkylarylation of alkenyl N-heteroarenes with α-bromocarboxylates and aryl boronic acids is reported. The protocol provides a new method to access a variety of N-heteroarene substituted diarylalkanes in moderate to good yields. It features mild reaction conditions, cheap nickel catalyst, readily available substrates, and broad substrate scope.

NiH-Catalyzed Regio- and Enantioselective Hydroalkylation for the Synthesis of β- or γ-Branched Chiral Aromatic N-Heterocycles

A nickel hydride-catalyzed regio- and enantioselective hydroalkylation reaction was developed to give access to a library of chiral β- or γ-branched aromatic N-heterocycles. This intriguing asymmetric transformation features excellent selectivities, step- and atom-economies, and generating two kinds of chiral products through one synthetic strategy. Furthermore, the possible reaction mechanism was extensively investigated using numerous control experiments and density functional theory calculations.

Catalytic Synthesis of β-(Hetero)arylethylamines: Modern Strategies and Advances

β-(Hetero)arylethylamines appear in a myriad of pharmaceuticals due to their broad spectrum of biological properties, making them prime candidates for drug discovery. Conventional methods for their preparation often require engineered substrates that limit the flexibility of the synthetic routes and the diversity of compounds that can be accessed. Consequently, methods that provide rapid and versatile access to those scaffolds remain limited. To overcome these challenges, synthetic chemists have designed innovative and modular strategies to access the β-(hetero)arylethylamine motif, paving the way for their more extensive use in future pharmaceuticals. This review outlines recent progresses in the synthesis of (hetero)arylethylamines and emphasizes how these innovations have enabled new levels of molecular complexity, selectivity, and practicality.

Applications of Hantzsch Esters in Organocatalytic Enantioselective Synthesis

Hantzsch esters (1,4-dihydropyridine dicarboxylates) have become, in this century, very versatile reagents for enantioselective organic transformations. They can act as hydride transfer agents to reduce, regioselectively, a variety of multiple bonds, e.g., C=C and C=N, under mild reaction conditions. They are excellent reagents for the dearomatization of heteroaromatic substances, and participate readily in cascade processes. In the last few years, they have also become useful reagents for photoredox reactions. They can participate as sacrificial electron and hydrogen donors and when 4-alkyl or 4-acyl-substituted, they can act as alkyl or acyl radical transfer agents. These last reactions may take place in the presence or absence of a photocatalyst. This review surveys the literature published in this area in the last five years.

Kinetic Resolution of Azaarylethynyl Tertiary Alcohols by Chiral Brønsted Acid Catalysed Phosphine-Mediated Deoxygenation

A chiral Brønsted acid catalysed phosphine-mediated deoxygenation protocol is reported. This metal-free method provides a precise kinetic resolution platform for azaarylethynyl tertiary alcohols, which are a broad category of biologically and synthetically important azaarene derivatives. In addition to providing an efficient method for the first asymmetric preparation of these tertiary alcohols, the strategy facilitates the construction of azaaryl-functionalized allenes with good to excellent enantioselectivities. The high selectivity factors (s up to 235), broad substrate scope, and ability to convert azaaryl compounds into both chiral tertiary alcohols and allenes robustly underscore the efficiency and promising utility of this method. The practicability is further validated by the successful synthesis of deuterated allenes with high ee values and substantial incorporation of deuterium using inexpensive D₂ O as the deuterium source.

Enantioselective [3 + 2] Cycloaddition of Vinylcyclopropanes with Alkenyl N-Heteroarenes Enabled by Palladium Catalysis

The first catalytic enantioselective [3 + 2] cycloaddition reaction between vinylcyclopropanes and alkenyl N-heteroarenes in the presence of LiBr and a Pd(0)/SEGPHOS complex was developed. LiBr plays a key role in improving the reactivity of alkenyl N-heteroarenes as a mild Lewis acid.

Asymmetric Synthesis of Heterocyclic Chloroamines and Aziridines by Enantioselective Protonation of Catalytically Generated Enamines

We report a method for the synthesis of chiral vicinal chloroamines via asymmetric protonation of catalytically generated prochiral chloroenamines using chiral Brønsted acids. The process is highly enantioselective, with the origin of asymmetry and catalyst substituent effects elucidated by DFT calculations. We show the utility of the method as an approach to the synthesis of a broad range of heterocycle-substituted aziridines by treatment of the chloroamines with base in a one-pot process, as well as the utility of the process to allow access to vicinal diamines.

Highly enantioselective δ-protonation and formal [3 + 3] annulation promoted by N-heterocyclic carbene

A chiral NHC catalyst reacts with α,β-γ,δ-diunsaturated aldehydes to generate an extended Breslow intermediate. Upon δ-protonation and tautomerization, the resulting α,β-unsaturated acyl azolium undergoes [3 + 3] annulation with enamines to afford various dihydropyridinones.

Observation of macrophage autophagy in the healing of diabetic ulcers via a lysosome-targeting polarity-specific two-photon probe

As a disease with high incidence, mutilation, and fatality rates, diabetic ulcers (DUs) have become a difficult and complicated disease of widely concern in recent years due to the unclear healing mechanism. The main reason for the delayed healing in DU patients is the unduly long chronic inflammation window, and the polarization state of macrophages plays a key role in this process. Since autophagy is believed to be closely related to the polarization trend of macrophages, recent studies have shown that autophagy is closely related to the healing of DU. To this end, a lysosome-targeting polarity-sensitive probe, XZTU-VIS, was developed to monitor the changes in lysosomal polarity, thereby assessing the autophagy of macrophages in mice suffering from DU. The experimental results showed that under two-photon fluorescence microscopy, the green channel fluorescence signal of XZTU-VIS decreased significantly during autophagy. In the meantime, DU models established using BV-2 cells and mice showed a process that could cause inflammation and the release of ROS, thereby inducing autophagy.

A polarity-dependent two-photon fluorescent probe for evaluation of autophagy in the process of diabetic mouse skin ulcer-induced inflammation was constructed.

Radical-based functionalization-oriented construction: rapid assembly of azaarene-substituted highly functionalized pyrroles

Totally different functionalization and construction as two fundamental synthetic protocols have long been applied to furnish azaarene variants. Here, a novel radical-based functionalization-oriented construction strategy by exploiting the electronic properties of azaarenes and the high reactivity of radicals is developed. Under a photoredox catalysis platform, the robust ability of such an artful combination of functionalization with construction is disclosed in the synthesis of valuable 3-azaarene-substituted densely functionalized pyrroles. In addition to the ability to use the readily accessible feedstocks, the high synthetic efficiency and the good functional group tolerance, the substrate scope is broad (81 examples) resulting from the capability to flexibly replace the types of azaarenes and other substituents. Control experiments and density functional theory (DFT) calculations elucidate the plausible mechanism involving the reaction pathways and the important role of NaH2PO4 as an additive in the reaction.

Enantioselective Protonation: Hydrophosphinylation of 1,1-Vinyl Azaheterocycle N-Oxides Catalyzed by Chiral Bis(guanidino)iminophosphorane Organosuperbase

Enantioselective protonation by hydrophosphinylation of diarylphosphine oxides with 2-vinyl azaheterocycle N-oxide derivatives was demonstrated using chiral bis(guanidino)iminophosphorane as the higher-order organosuperbase catalyst. It was confirmed by several control experiments that a chiral weak conjugate acid of the chiral bis(guanidino)iminophosphorane, instead of achiral diarylphosphine oxides, directly functioned as the proton source to afford the corresponding product in a highly enantioselective manner in most cases. Enantioselective protonation by a weak conjugate acid generated from the higher-order organosuperbase would broaden the scope of enantioselective reaction systems because of utilization of a range of less acidic pronucleophiles. This method is highlighted by the valuable synthesis of a series of chiral P,N-ligands for chiral metal complexes through the reduction of phosphine oxide and N-oxide units of the corresponding product without loss of enantiomeric purity.

Catalytic Enantioselective Synthesis of Heterocyclic Vicinal Fluoroamines by Using Asymmetric Protonation: Method Development and Mechanistic Study

A catalytic enantioselective synthesis of heterocyclic vicinal fluoroamines is reported. A chiral Brønsted acid promotes aza-Michael addition to fluoroalkenyl heterocycles to give a prochiral enamine intermediate that undergoes asymmetric protonation upon rearomatization. The reaction accommodates a range of azaheterocycles and nucleophiles, generating the C-F stereocentre in high enantioselectivity, and is also amenable to stereogenic C-CF3 bonds. Extensive DFT calculations provided evidence for stereocontrolled proton transfer from catalyst to substrate as the rate-determining step, and showed the importance of steric interactions from the catalyst's alkyl groups in enforcing the high enantioselectivity. Crystal structure data show the dominance of noncovalent interactions in the core structure conformation, enabling modulation of the conformational landscape. Ramachandran-type analysis of conformer distribution and Protein Data Bank mining indicated that benzylic fluorination by this approach has the potential to improve the potency of several marketed drugs.

Enantioselective [4 + 2] Cycloaddition Reaction of Vinylquinolines with Dienals Enabled by Synergistic Organocatalysis

An unprecedented organocatalytic enantioselective [4 + 2] cycloaddition reaction of vinyl quinolines with dienals is achieved with the synergistic activation of CH₃SO₃H and a chiral aminocatalyst. The power of the process is demonstrated by its high efficiency of the production of new synthetically and biologically valued chiral quinoline architectures in high yields and with excellent enantioselectivities.

Cooperative photoredox and chiral hydrogen-bonding catalysis

Chiral hydrogen-bonding catalysis is a classic strategy in asymmetric organocatalysis. Recently, it has been used to cooperate with photoredox catalysis, becoming a powerful tool to access optical pure compounds via radical-based transformations.

Pictet–Spengler reaction based on in situ generated α-amino iminium ions through the Heyns rearrangement

A useful tandem reaction via the Heyns rearrangement and Pictet–Spengler reaction was developed which ensured the synthesis of complex N-heteropolycycles containing tetrahydro-β-carboline with high yield (up to 96%) and dr (99 : 1).

Photoredox-Catalyzed Enantioselective α-Deuteration of Azaarenes with D2O

The site-specific incorporation of deuterium (D) into small molecules is frequently used to access isotopically labeled compounds with broad utility in many research areas, such as drug development, mechanistic studies, and NMR analyses. Nevertheless, the deuteration of a stereocenter in an enantioselective manner, which could slow the metabolism and improve the bioavailability of bioactive molecules, remains challenging owing to the lack of established catalytic methods. Here, we report an asymmetric α-deuteration strategy for azaarenes with inexpensive D₂O as the deuterium source. A cooperative visible light-driven photoredox and chiral Brønsted acid–catalyzed system using a Hantzsch ester as the terminal reductant has been developed, which enables racemic α-chloro-azaarenes and prochiral azaarene-substituted ketones to experience a single-electron reduction–enantioselective deuteration process. The transition metal-free method provides important chiral α-deuterated azaarenes in satisfactory yields with good to excellent enantioselectivities (up to 99% ee) and substantial deuterium incorporation.

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Enantioselective deuteration enabled by photoredox asymmetric catalysis

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D₂O as the deuterium source

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Azaarenes with a deuterated stereocenter

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Transition-metal-free catalyst system

Organocatalytic aza-Michael Reaction to 3-Vinyl-1,2,4-triazines as a Valuable Bifunctional Platform

An unprecedented catalytic aza-Michael addition to substituted 3-vinyl-1,2,4-triazines, as original bifunctional platforms for the domino conjugate addition inverse-electron-demand hetero-Diels-Alder/retro-Diels-Alder ( ihDA/ rDA) reaction, was achieved using the highly acidic triflimide as an organocatalyst. Based on the use of alkoxyamine nucleophiles, this sequence not only highlights a rare example of the catalytic aza-Michael reaction to alkenylazaarenes but also proves to be useful for the elaboration of an array of biorelevant tetrahydro-[1,6]-naphthyridines.

Enantioselective reduction of azaarene-based ketones via visible light-driven photoredox asymmetric catalysis

An enantioselective reduction of azaarene-based ketones through photoredox asymmetric catalysis is reported.