Enantioselective Pallada-Electrocatalyzed C-H Activation by Transient Directing Groups: Expedient Access to Helicenes

Ether-Directed Enantioselective C(sp2)-H Borylation for the Synthesis of Axially Chiral Biaryls

We report an ether-directed enantioselective C(sp2)-H borylation catalyzed by a chiral bidentate boryl ligand (CBL)/iridium system for constructing axially chiral biaryls. This method delivered diverse chiral biaryls with good to high enantioselectivities, accommodating varied electronic and steric substituents on the aryl rings. Gram-scale synthesis and downstream transformations of the C-B bond underscored its practicality.

Organocatalytic Atroposelective Cross-Coupling of 2-Naphthols with Diaryliodonium Salts

Due to their modularity and conciseness, atroposelective cross-coupling is one of the most attractive approaches for synthesizing axially chiral binaphthyl molecules. While transition metal-catalyzed cross-couplings provide reliable synthetic strategies, alternative methods that accommodate a broader range of substrates without their pre-functionalization are highly beneficial. Here, we demonstrate that using the bifunctional organocatalyst (DHQD)2PHAL enables atroposelective cross-coupling of 2-naphthols and diaryliodonium salts with high efficiency, and yields (up to 72%) and excellent enantioselectivity (up to >99% enantiomeric excess). Further transformations of the products highlight the versatility of other binaphthyl compounds while maintaining their axial chirality.

Synthesis of Axially Chiral Compounds via Transition Metal-Catalyzed Atroposelective C-H Functionalization

ConspectusAxially chiral skeletons are prevalent in natural products and biologically important compounds, and they are widely utilized as privileged scaffolds in enantioselective catalysis. Consequently, the catalytic atroposelective synthesis of enantiopure atropisomers has garnered considerable attention. A variety of synthetic strategies involving metal catalysis or organocatalysis have been developed. Among these elegant approaches, transition metal-catalyzed enantioselective C-H activation has emerged as an atom- and step-economical strategy to streamline the construction of axially chiral compounds in recent years.In this Account, we discuss our efforts in the atroposelective synthesis of different types of axially chiral compounds, including biaryls, atropisomeric styrenes, and C-N atropisomers, via transition metal-catalyzed enantioselective C-H activation strategies. To this end, we have developed several approaches, including the chiral transient directing group (cTDG) strategy using catalytic Pd(OAc)2 and tert-leucine (Tle), as well as catalytic enantioselective systems involving Pd(II)/chiral phosphoric acid (CPA), Pd(II)/l-pyroglutamic acid (pGlu), Pd(0)/norbornene cooperative catalysis with a chiral biimidazoline (BiIM) ligand, and Co(II)/salicyloxazoline (Salox).At the outset, we successfully applied the cTDG strategy to access axially chiral biaryl aldehydes through Pd-catalyzed atroposelective C-H olefination, alkynylation, allylation, naphthylation, and alkylation. The efficacy of these methods has been demonstrated in the enantioselective synthesis of chiral aldehyde catalysts and natural products, such as TAN-1085, (+)-isochizandrin, and (+)-steganone. To facilitate the synthesis of biaryl atropisomers with diverse functionalities, we developed a novel Pd(II)/CPA catalytic system, which enables the preparation of various axially chiral quinolines, biaryl-2-amines, and atropisomeric biaryls bearing chalcogenoether units with high enantioselectivities. The Pd(II)/CPA system also allows for the synthesis of more challenging conjugated diene-based axially chiral styrenes.Nonbiaryl atropisomers, such as axially chiral styrenes and anilides, present synthetic challenges due to their conformational instability and higher degree of rotational freedom compared to their biaryl counterparts. We have addressed these challenges and achieved the highly efficient synthesis of atropisomeric styrenes and anilides using Pd(II)/pGlu and Pd(0)/norbornene/BiIM catalysis. In addition to palladium catalysis, cobalt(II)/Salox catalysis has also been developed for the construction of chiral biaryls, atropisomers with vicinal C-N and C-C stereogenic axes, remote distinct C-N diaxes, and chiral calix[4]arenes featuring both inherent and axial chirality. We anticipate that the enantioselective C-H activation strategy will find broad applications in the construction of synthetically useful axially chiral compounds.

Enantioselective electrochemical nickel-catalyzed vinylogous radical reactions

Highly functionalized structural motifs with extended chiral carbon chains are prevalent in a wide range of bioactive compounds and play critical roles in the production of various functionalized molecules. Here, we describe a nickel-catalyzed asymmetric radical-based electrochemical functionalization of silyl polyenolates at α-, γ-, ε-, and η-positions. Driven by electric current, this methodology provides a sustainable route to access enantioenriched dicarbonyls via vinylogous radical pathways. It demonstrates excellent functional groups tolerance, mild reaction conditions, broad substrate compatibility, formation of quaternary stereocenters at remote positions, and high levels of regio- and enantioselectivity (up to 98% enantiomeric excess). Mechanistic investigations indicate that ferrocene-based electron transfer mediators are pivotal in the anodic oxidation process, facilitating the generation of nickel-bound α-carbonyl radicals while suppressing the undesired oxidation of silyl polyenolates, thus guiding the selection of mediators for electrocatalytic systems. The versatility of catalytic asymmetric electrosynthesis is highlighted by the preparation of valuable enantioenriched building blocks and the total synthesis of (-)-ethosuximide.

Parametrization of κ2-N,O-Oxazoline Preligands for Enantioselective Cobaltaelectro-Catalyzed C-H Activations

Enantioselective electrocatalyzed C-H activations have emerged as a transformative platform for the assembly of value-added chiral organic molecules. Despite the recent progress, the construction of multiple C(sp3)-stereogenic centers via a C(sp3)-C(sp3) bond formation has thus far proven to be elusive. In contrast, we herein report an annulative C-H activation strategy, generating chiral Fsp3-rich molecules with high levels of diastereo- and enantioselectivity. κ2-N,O-oxazoline preligands were effectively employed in enantioselective cobalt(III)-catalyzed C-H activation reactions. Using DFT-derived descriptors and regression statistical modeling, we performed a parametrization study on the modularity of chiral κ2-N,O-oxazoline preligands. The study resulted in a model describing ligands' selectivity characterized by key steric, electronic, and interaction behaviors.

Construction of Axially Chiral Dialdehydes via Rhodium-Catalyzed Enantioselective C-H Amidation

Achieving axially chiral biaryl dialdehydes through asymmetric catalysis remains significantly challenging due to the lack of efficient strategies. In this report, we developed a rhodium-catalyzed enantioselective C-H amidation through chiral transient directing group strategy. With this new approach, a series of axially chiral amido dialdehydes were achieved in up to 86 % yields with 99.5 : 0.5 er. Furthermore, detailed mechanistic studies indicated that both the imine formation and C-H bond cleavage steps were reversible. More interestingly, the X-ray crystallographic analysis of Int-2 showed probable C-H/π interaction between biaryl group and chiral amine moiety. This process offered a convenient route to access axially chiral dialdehyde derivatives. More broadly, it demonstrated a new tool through transient and C-H/π synergistic interactions, which would stimulate further development of asymmetric catalytic system in enantioselective C-H functionalization.

Enantioselective Multicomponent Electrochemical Difunctionalization of Terminal Alkynes

The direct functionalization of alkyne triple bonds using a radical strategy provides an efficient platform for creating a wide range of substituted alkenes. However, developing a multicomponent enantioselective radical reaction using feedstock alkynes to forge all-carbon quaternary stereocenters─while addressing challenges related to compatibility, selectivity, and efficiency─remains relatively rare. Here we report an enantioselective electrochemical nickel-catalyzed three-component cross-coupling of readily available terminal alkynes, diverse racemic alkyl radical precursors, and group transfer reagents (such as (TMS)3Si-H, RSe-SeR, RTe-TeR, and CHI3), achieving excellent regio-, stereo-, and enantioselectivities (more than 70 examples, up to 95% ee). Electricity-mediated difunctionalizations significantly expand the scope of both aliphatic and aromatic alkynes, demonstrating excellent functional group compatibility. The key to success lies in the rational design of anodically generated nickel-bound tertiary radical intermediates, which stereoselectively capture alkynes to form vinyl radicals and participate in subsequently diverse group transfer processes to enable the intermolecular and anti-stereoselective difunctionalization of alkynes. This approach allows the transformation of terminal alkynes into diverse structural entities with α-quaternary stereogenic centers.

Recent Advances in Asymmetric Organometallic Electrochemical Synthesis (AOES)

ConspectusIn recent years, our research group has dedicated significant effort to the field of asymmetric organometallic electrochemical synthesis (AOES), which integrates electrochemistry with asymmetric transition metal catalysis. On one hand, we have rationalized that organometallic compounds can serve as molecular electrocatalysts (mediators) to reduce overpotentials and enhance both the reactivity and selectivity of reactions. On the other hand, the conditions for asymmetric transition metal catalysis can be substantially improved through electrochemistry, enabling precise modulation of the transition metal's oxidation state by controlling electrochemical potentials and regulating the electron transfer rate via current adjustments. This synergistic approach addresses key challenges inherent in traditional asymmetric transition metal catalysis, particularly those related to the use of redox-active chemical reagents. Furthermore, the redox potentials of molecular electrocatalysts can be conveniently tuned by modifying their ligands, thereby governing the reaction regioselectivity and stereoselectivity. As a result, the AOES has emerged as a powerful and promising tool for the synthesis of chiral compounds.In this Account, we summarize and contextualize our recent efforts in the field of AOES. Our primary strategy involves leveraging the controllability of electrochemical potential and current to regulate the oxidation state of organometallics, thereby facilitating the desired reactions. An efficient asymmetric synthesis platform was established under mild conditions, significantly reducing the reliance on chemical redox reagents. Our research has been systematically categorized into three sections based on distinct electrolysis modes: asymmetric transition metal catalysis combined with anodic oxidation, cathodic reduction, and paired electrolysis. In each section, we highlight our innovative discoveries tailored to the unique characteristics of the respective electrolysis modes.In many transformations, transition metal-catalyzed reactions involving traditional chemical redox reagents and those utilizing electrochemistry exhibit similar reactivities. However, we also observed notable differences in certain cases. These findings include the following: (1) Enhanced efficiency in asymmetric electrochemical synthesis: for instance, the Rh-catalyzed enantioselective electrochemical functionalization of C-H bonds demonstrates superior efficiency. (2) Expanded scope of transformations: certain transformations, previously challenging in traditional transition metal catalysis, can be achieved through electrochemistry due to the tunability of redox potentials. A notable example is the enantioselective reductive coupling of aryl chlorides, which significantly expands the range of accessible transformations. Additionally, our mechanistic studies explore unique techniques intrinsic to electrochemistry, such as controlled potential electrolysis experiments, the impact of electrode materials on catalyst performance, and cyclic voltammetry studies. These investigations provide a more intuitive understanding of the behavior of metal catalysts through the study of electrochemical mechanisms, which can also guide the design of new catalytic systems.The advancements in this field offer a robust platform for environmentally friendly and sustainable selective asymmetric transformations. By integrating electrochemistry with transition metal catalysis, we have developed a versatile approach for organic synthesis that not only enhances the efficiency and selectivity of reactions but also reduces the environmental impact. We anticipate that this Account will stimulate further research and innovation in the realm of AOES, leading to the discovery of new catalytic systems and the development of more sustainable synthetic methodologies.

Enantiopure Turbo Chirality Targets in Tri-Propeller Blades: Design, Asymmetric Synthesis, and Computational Analysis

Enantiopure turbo chirality in small organic molecules, without other chiral elements, is a fascinating topic that has garnered significant interest within the chemical and materials science community. However, further research into and application of this concept have been severely limited by the lack of effective asymmetric tools. To date, only a few enantiomers of turbo chiral targets have been isolated, and these were obtained through physical separation using chiral HPLC, typically on milligram scales. In this work, we report the first asymmetric approach to enantiopure turbo chirality in the absence of other chiral elements such as central and axial chirality. This is demonstrated by assembling aromatic phosphine oxides, where three propeller-like groups are anchored to a P(O) center via three axes. Asymmetric induction was successfully carried out using a chiral sulfonimine auxiliary, with absolute configurations and conformations unambiguously determined by X-ray diffraction analysis. The resulting turbo frameworks exhibit three propellers arranged in either a clockwise (P,P,P) or counterclockwise (M,M,M) configuration. In these arrangements, the bulkier sides of the aromatic rings are oriented toward the oxygen atom of the P=O bond rather than in the opposite direction. Additionally, the orientational configuration is controlled by the sulfonimine auxiliary as well, showing that one of the Naph rings is pushed away from the auxiliary group (-CH2-NHSO2-tBu) of the phenyl ring. Computational studies were conducted on relative energies for the rotational barriers of a turbo target along the P=O axis and the transition pathway between two enantiomers, meeting our expectations. This work is expected to have a significant impact on the fields of chemistry, biomedicine, and materials science in the future.

Enantioselective Electrocatalysis for Cross-Dehydrogenative Heteroarylation with Indoles, Pyrroles, and Furans

Oxidative cross-dehydrogenative C-H/C-H functionalizations represent an exemplary approach for synthesizing carbonyl compounds via α-heteroarylation. Here we present the development of a direct anodic oxidative coupling process between 2-acylimidazoles and divergent heterocyclic systems including indole, pyrrole, and furan, facilitated by ferrocene-assisted asymmetric nickel electrocatalysis with high levels of enantioselectivity. Mechanistic investigations indicate that the reaction initially involves the formation of a chiral Ni-bound α-carbonyl radical, which is then captured by the heteroarene radical cation via intermolecular stereoselective radical/radical cation coupling. The mild, scalable, and robust reaction conditions allow for a broad substrate scope and excellent functional group tolerance, enabling access to a wide range of chiral hetero-compounds. The consequential α-heteroaromatic carbonyl products can potentially be transformed into a plethora of synthetically valuable frameworks, as exemplified by their application in the asymmetric total synthesis of (-)-COX-2 inhibitor, (+)-acremoauxin A, and (+)-pemedolac.

Enantioselective nickel-catalyzed electrochemical reductive conjugate alkenylation of α,β-unsaturated ketones

Catalytic electrochemical asymmetric catalysis is emerging as a promising strategy for the synthesis of chiral compounds. Herein, we report an asymmetric electrochemical nickel-catalysed reductive conjugate addition of alkenyl bromides/aryl iodides to α,β-unsaturated ketones in an undivided cell, leading to addition products with high yields and excellent enantioselectivities (up to 96% yield and 96% ee).

Enantioselective Nickel-Electrocatalyzed Cross-Dehydrogenative α- and γ-Nitroalkylation

Asymmetric catalytic versions of electricity-driven processes hold immense potential for the sustainable preparation of chiral compounds. However, the involvement of anodic oxidative cross-dehydrogenative coupling events between two distinct nucleophiles makes it challenging for a chiral catalyst to regulate the stereochemistry of the products. Our current electrocatalytic strategy for enantioconvergent cross-dehydrogenative α- and γ-nitroalkylation via radical-based pathways produces an array of enantioenriched nitroesters without supplementary stoichiometric oxidants. Mechanistic investigations reveal that the nickel catalyst plays a key role in both the electrochemical activation of the substrates and the stereoselectivity-defining events, affording the electrochemically generated Lewis acid-bound α-carbonyl radicals to interact with in situ-generated nitronate anions in a stereoselective manner. This electrocatalytic approach enables transformations that are highly challenging under thermal conditions, such as umpolung reactivity with readily available substrates, all-carbon quaternary stereocenter creation, and the control of remote stereochemistry.

Rhodaelectro-Catalyzed Synthesis of Pyrano[3,4-b]indol-1(9H)-ones via the Double Dehydrogenative Heck Reaction between Indole-2-carboxylic Acids and Alkenes

A rhodaelectro-catalyzed double dehydrogenative Heck reaction of indole-2-carboxylic acids with alkenes has been developed for the synthesis of pyrano[3,4-b]indol-1(9H)-ones. The weakly coordinating carboxyl group is utilized twice as a directing group to activate the C-H bonds throughout the reaction. This reaction precedes an acceptorless dehydrogenation under exogenous oxidant-free conditions in an undivided cell with a constant current.

Construction of axially chiral 2-arylpyrroles using catalytic asymmetric Suzuki-Miyaura cross-coupling: an efficient approach to esaxerenone

A general and efficient method has been developed to access axially chiral 2-arylpyrroles using catalytic asymmetric Suzuki-Miyaura cross-coupling. A wide range of axially chiral arylpyrroles were obtained in high yields with good to excellent enantioselectivities. The key to success is the use of a combined catalytic system involving a palladium catalyst and chiral ferrocene diphosphine ligand for achieving effective enantiocontrol. More importantly, this axially chiral CF3-substituted 2-arylpyrrole serves as a key intermediate in the preparation of the anti-hypertensive and diabetic nephropathy drug esaxerenone. It was directly asymmetrically synthesized with high enantioselectivity (92% ee). Thus, a new strategy is provided for the catalytic asymmetric synthesis of esaxerenone.

Metallaelectro-catalyzed alkyne annulations via C-H activations for sustainable heterocycle syntheses

Alkyne annulation represents a versatile and powerful strategy for the assembly of structurally complex compounds. Recent advances successfully enabled electrocatalytic alkyne annulations, significantly expanding the potential applications of this promising technique towards sustainable synthesis. The metallaelectro-catalyzed C-H activation/annulation stands out as a highly efficient approach that leverages electricity, combining the benefits of electrosynthesis with the power of transition-metal catalyzed C-H activation. Particularly attractive is the pairing of the electro-oxidative C-H activation with the valuable hydrogen evolution reaction (HER), thereby addressing the growing demand for green energy solutions. Herein, we provide an overview of the evolution of electrochemical C-H annulations with alkynes for the construction of heterocycles, with a topical focus on the underlying mechanism manifolds.

Synthesis of chiral systems featuring the pyrrole unit: a review

Synthetic strategies towards pyrroles within chiral frameworks are summarised, focussing on reports published 2010-2023. The synthesis of pyrroles featuring substituents bearing chiral centres are summarised, as are those whereby pyrroles are located within axially chiral systems courtesy of restricted bond rotation.

Catalytic Asymmetric Reductive Amination for Axially Chiral Aryl Aldehydes via Desymmetrization/Kinetic Resolution Cascade

Herein we present an efficient chiral phosphoric-acid-catalyzed atropoenantioselective asymmetric reductive amination of biaryl dialdehydes. The process involves desymmetrization and the following kinetic resolution, with a wide range of axially chiral aryl aldehydes obtained with high optical purities.

Cobaltaelectro-Catalyzed C-H Activation for Central and Axial Double Enantio-Induction

In recent years, enantioselective electrocatalysis has surfaced as an increasingly-effective platform for sustainable molecular synthesis. Despite indisputable progress, strategies that allow the control of two distinct stereogenic elements with high selectivity remain elusive. In contrast, we, herein, describe electrochemical cobalt-catalyzed C-H activations that enable the installation of chiral stereogenic centers along with a chiral axis with high levels of enantio- and diastereoselectivities. The developed electrocatalysis strategy allowed for C-H/N-H activations/annulations with cyclic and non-cyclic alkenes providing expedient access to various central as well as atropo-chiral dihydroisoquinolinones paired to the valuable hydrogen evolution reaction. Studies on the atropo-stability of the obtained compounds demonstrated that the exceedingly mild conditions ensured by the electrocatalytic process were key for the achieved high stereoselectivities.

Crafting 1,4-diaryl spirobifluorene hosts in OLEDs via interannular C-H arylation: synergistic effects of molecular linearity and orthogonality

In this work, we present a design concept of introducing linear structures into the orthogonal configuration of 9,9'-spirobifluorene (SBF), aiming to enhance carrier mobilities while maintaining high triplet energies (E T), which are two critical parameters for optimizing host materials in organic light-emitting diodes (OLEDs). To validate our proposed design, four pivotal model molecules of 1,4-diaryl SBFs were synthesized via interannular C-H arylation of bi(hetero)aryl-2-formaldehydes, a task challenging to accomplish using previous synthetic methodologies. The orthogonal configuration and the steric hindrance of SBF lead to high E T through the conjugation breaking at C1 and C4 positions, rendering 1,4-diaryl SBFs suitable as universal pure hydrocarbon (PHC) hosts for red, green, and blue (RGB) phosphorescent OLEDs (PhOLEDs). Meanwhile, the linearity and relatively good planarity of the para-quaterphenyl structure promote high carrier mobilities through orderly intermolecular packing. The synergistic effects of linearity and orthogonality in 1-(para-biphenyl)-4-phenyl-SBF result in exceptional device performance with external quantum efficiencies (EQEs) of 26.0%, 26.1%, and 22.5% for RGB PhOLEDs, respectively. Notably, the green PhOLED exhibits minimal efficiency roll-off, positioning its device performances among the state-of-the-art in PHC hosts.

Atroposelective catalysis

Atropisomeric compounds-stereoisomers that arise from the restricted rotation about a single bond-have attracted widespread attention in recent years due to their immense potential for applications in a variety of fields, including medicinal chemistry, catalysis and molecular nanoscience. This increased interest led to the invention of new molecular motors, the incorporation of atropisomers into drug discovery programmes and a wide range of novel atroposelective reactions, including those that simultaneously control multiple stereogenic axes. A diverse set of synthetic methodologies, which can be grouped into desymmetrizations, (dynamic) kinetic resolutions, cross-coupling reactions and de novo ring formations, is available for the catalyst-controlled stereoselective synthesis of various atropisomer classes. In this Review, we generalize the concepts for the catalyst-controlled stereoselective synthesis of atropisomers within these categories with an emphasis on recent advancements and underdeveloped atropisomeric scaffolds beyond stereogenic C(sp2)-C(sp2) axes. We also discuss more complex systems with multiple stereogenic axes or higher-order stereogenicity.

Chiral amino acids: evolution in atroposelective C-H activation

This review covers the journey of chiral amino acids as ligands in atroposelective C-H bond activation/functionalization via transition metal catalysis. Herein, we intend to demonstrate how these chiral amino acids have evolved and flourished in this stimulating field. Unprotected amino acids, mono-N-protected amino acids, and di-N-protected amino acids have been devised for atroposelective C-H activation. In each section, we have briefly discuss the key successes of amino acids in the atroposelective synthesis of biaryls, heterobiaryls, and non-biaryl atropisomers and their advantages in atroposelective C-H activation.

Atroposelective N-N Axes Synthesis via Electrochemical Cobalt Catalysis

Here, we disclosed an unprecedented cobalt electrocatalyzed atroposelective C-H activation and annulation for the efficient construction of diversely functionalized N-N axes in an undivided cell. A broad range of allene substrates and benzamides bearing different functionalities are compatible with generating axially chiral products with good yields and excellent enantioselectivities (up to 92% yield and 99% ee). A series of synthetic applications and control experiments were also performed, which further expanded the practicality of this strategy.

Electrochemical Enantioselective C-H Annulation by Achiral Rhodium(III)/Chiral Brønsted Base Domino Catalysis

Rhodium(III)-catalyzed enantioselective C-H activation has emerged as a powerful tool for assembling enabling chiral molecules. However, this approach is significantly hampered by the cumbersome synthetic routes for preparing chiral rhodium catalysts. In sharp contrast, we herein report on an electrochemical domino catalysis system that exploits an achiral Cp*-rhodium catalyst along with an easily accessible chiral Brønsted base for an enantioselective C-H activation/annulation reaction of alkenes by benzoic acids. Our strategy offers an environmentally benign and most user-friendly approach for assembling synthetically useful chiral phthalides in good enantioselectivity, employing electricity as the sustainable oxidant.

Enantioselective Nickel-Electrocatalyzed Reductive Propargylic Carboxylation with CO2

The exploitation of carbon dioxide (CO2) as a sustainable, plentiful, and harmless C1 source for the catalytic synthesis of enantioenriched carboxylic acids has long been acknowledged as a pivotal task in synthetic chemistry. Herein, we present a current-driven nickel-catalyzed reductive carboxylation reaction with CO2 fixation, facilitating the formation of C(sp3)-C(sp2) bonds by circumventing the handling of moisture-sensitive organometallic reagents. This electroreductive protocol serves as a practical platform, paving the way for the synthesis of enantioenriched propargylic carboxylic acids (up to 98% enantiomeric excess) from racemic propargylic carbonates and CO2. The efficacy of this transformation is exemplified by its successful utilization in the asymmetric total synthesis of (S)-arundic acid, (R)-PIA, (S)-chizhine D, (S)-cochlearin G, and (S,S)-alexidine, thereby underscoring the potential of asymmetric electrosynthesis to achieve complex molecular architectures sustainably.

Enantioselective nickel-catalyzed anodic oxidative dienylation and allylation reactions

Precision control of stereochemistry in radical reactions remains a formidable challenge due to the prevalence of incidental racemic background reactions resulting from undirected substrate oxidation in the absence of chiral induction. In this study, we devised an thoughtful approach-electricity-driven asymmetric Lewis acid catalysis-to circumvent this impediment. This methodology facilitates both asymmetric dienylation and allylation reactions, resulting in the formation of all-carbon quaternary stereocenters and demonstrating significant potential in the modular synthesis of functional and chiral benzoxazole-oxazoline (Boox) ligands. Notably, the involvement of chiral Lewis acids in both the electrochemical activation and stereoselectivity-defining radical stages offers innovative departures for designing single electron transfer-based reactions, significantly underscoring the relevance of this approach as a multifaceted and universally applicable strategy for various fields of study, including electrosynthesis, organic chemistry, and drug discovery.

Padlocking dihydrofurannulation for the control of small degree of helicity built on a fused-tetracyclic core

Enantioselective construction of small molecules displaying a configurationally stable helical shape built on a fused-tetracyclic core is a daunting synthetic challenge even more pronounced when five-membered rings are incorporated in the structure. The resulting higher configurational lability strongly hampers their access, and therefore the development of new efficient methodologies is timely and highly desirable. In this context, we describe a padlocking approach via the enantioselective organocatalytic domino furannulation of appropriately designed achiral fused-tricyclic precursors resulting in the synthesis of configurationally locked helically chiral tetracyclic scaffolds featuring one or two five-membered rings with the simultaneous control of central and helical chiralities.

When is an Imine Directing Group a Transient Imine Directing Group in C-H Functionalization?

'Transient' C-H functionalization has emerged in recent years to describe the use of a dynamic linkage, often an imine, to direct cyclometallation and subsequent functionalization. As the field continues to grow in popularity, we consider the features that make an imine directing group transient. A transient imine should be i) formed dynamically in situ, ii) avoid discrete introduction or cleavage steps, and iii) offer the potential for catalysis in both the directing group and metal. This concept article contrasts transient imines with pioneering early studies of imines as directing groups for the formation of metallacycles and the use of preformed imines in C-H functionalization. Leading developments in the use of catalytic additives to form transient directing groups (as aldehyde or amine) are covered including selected highlights of the most recent examples of catalytic imine directed C-H functionalization with transition metals.

Catalytic asymmetric construction of helicenes via transformation of biaryls

This review showcases a systematic overview of the available tools for the catalytic asymmetric transformation of biaryl substrates toward the construction of challenging enantioenriched helicenes and the conceptual aspects associated with each type of transformation. Depending on the properties of the biaryl and the nature of the process, several methodologies have been developed, including olefin metathesis, hydroarylation of alkynes, C-X (X = C, O, N) coupling, and C-H functionalization. Pioneering studies and an array of representative reactions are discussed to underscore the potential of these synthetic protocols.

Electrooxidative Rhodium(III)/Chiral Carboxylic Acid-Catalyzed Enantioselective C-H Annulation of Sulfoximines with Alkynes

The combination of achiral Cp*Rh(III) with chiral carboxylic acids (CCAs) represents an efficient catalytic system in transition metal-catalyzed enantioselective C-H activation. However, this hybrid catalysis is limited to redox-neutral C-H activation reactions and the adopt to oxidative enantioselective C-H activation remains elusive and pose a significant challenge. Herein, we describe the development of an electrochemical Cp*Rh(III)-catalyzed enantioselective C-H annulation of sulfoximines with alkynes enabled by chiral carboxylic acid (CCA) in an operationally friendly undivided cell at room temperature. A broad range of enantioenriched 1,2-benzothiazines are obtained in high yields with excellent enantioselectivities (up to 99 % yield and 98 : 2 er). The practicality of this method is demonstrated by scale-up reaction in a batch reactor with external circulation. A crucial chiral Cp*Rh(III) intermediate is isolated, characterized, and transformed, providing rational support for a Rh(III)/Rh(I) electrocatalytic cycle.

Mechanism and Origin of Stereoselectivity for the NHC-Catalyzed Desymmetrization Reaction for the Synthesis of Axially Chiral Biaryl Aldehydes

Organocatalytic desymmetrization reaction is a powerful tool for constructing axial chirality, but the theoretical study on the origin of stereoselectivity still lags behind even now. In this work, the N-heterocyclic carbene (NHC)-catalyzed desymmetrization reaction of biaryl frameworks for the synthesis of axially chiral aldehydes has been selected and theoretically investigated by using density functional theory (DFT). The fundamental pathway involves several steps, i.e., desymmetrization, formation of Breslow oxidation, esterification, and NHC regeneration. The desymmetrization and formation of Breslow processes have been identified as stereoselectivity-determining and rate-determining steps. Further weak interaction analyses proved that the C-H···O hydrogen bond and C-H···π interactions are responsible for the stability of the key stereoselective desymmetrization transition states. This research contributes to understanding the nature of NHC-catalyzed desymmetrization reactions for the synthesis of axially chiral compounds.

Asymmetric Paired Electrocatalysis: Enantioselective Olefin-Sulfonylimine Coupling

Asymmetric electrocatalysis offers exciting new strategies for the synthesis of chiral molecules through novel reaction pathways. However, simultaneous activation of reactants on both electrodes via asymmetric paired electrolysis, which is more energy efficient and economic than single half-electrode synthesis, remains a formidable challenge. Herein, an asymmetric olefin-sulfonylimine coupling via paired electrocatalysis is presented for the first time. In this protocol, Co-catalyzed hydrogen atom transfer on the anode and Ni-catalyzed sulfonylimine reduction on the cathode were seamlessly cross-coupled. The new catalytic system enables the formation of chiral amine products bearing a tetrasubstituted carbon stereocenter with a high enantioselectivity (up to 96% ee).

Dual-Catalyzed Stereodivergent Electrooxidative Homocoupling of Benzoxazolyl Acetate

The development of a reliable strategy for stereodivergent radical reactions that allows convenient access to all stereoisomers of homocoupling adducts with multiple stereogenic centers remains an unmet goal in organic synthesis. Herein, we describe a dual-catalyzed electrooxidative C(sp3)-H/C(sp3)-H homocoupling with complete absolute and relative stereocontrol for the synthesis of molecules with contiguous quaternary stereocenters in a general and predictable manner. The stereodivergent electrooxidative homocoupling reaction is achieved by synergistically utilizing two distinct chiral catalysts that convert identical racemic substrates into inherently distinctive reactive chiral intermediates, dictate enantioselective radical addition, and allow access to the full complement of stereoisomeric products via simple catalyst permutation. The successful execution of the dual-electrocatalytic strategy programmed via electrooxidative activation provides a significant conceptual advantage and will serve as a useful foundation for further research into cooperative stereocontrolled radical transformations and diversity-oriented synthesis.

Access to Axially Chiral Aryl Aldehydes via Carbene-Catalyzed Nitrile Formation and Desymmetrization Reaction

An approach utilizing N-heterocyclic carbene for nitrile formation and desymmetrization reaction is developed. The process involves kinetic resolution, with the axially chiral aryl monoaldehydes obtained in moderate yields with excellent optical purities. These axially chiral aryl monoaldehydes can be conveniently transformed into functionalized molecules, showing great potential as catalysts in organic chemistry.

Mixed-Linker Chiral 2D Covalent Organic Frameworks with Controlled Layer Stacking for Electrochemical Asymmetric Catalysis

Covalent organic frameworks (COFs) have undergone extensive research as heterogeneous catalysts for a wide range of significant reactions, but they have not yet been investigated in the realm of electrochemical asymmetric catalysis, despite their recognition as an economical and sustainable strategy for producing enantiopure compounds. Here, we report a mixed-linker strategy to design multicomponent two-dimensional (2D) chiral COFs with tunable layer stacking for highly enantioselective electrocatalysis. By crystallizing mixtures of triamines with and without the MacMillan imidazolidinone catalyst or aryl substituent (ethyl and isopropyl) and a dialdehyde derivative of thieno-[3,2-b]thiophene, we synthesized and structurally characterized a series of three-component homochiral 2D COFs featuring either AA or ABC stacking. The stacking modes that can be synthetically controlled through steric tuning using different aryl substituents affect their chemical stability and electrochemical performance. With the MacMillan catalyst periodically appended on their channels, all three COFs with conductive thiophene moieties can be highly enantioselective and recyclable electrocatalysts for the asymmetric α-arylation of aldehydes, affording alkylated anilines with up to 97% enantiomeric excess by an anodic oxidation/organocatalytic protocol. Presumably due to their higher charge transfer ability, the ABC stacking COFs exhibit improved reactivity compared to the AA stacking analogue. This work therefore advances COFs as electrocatalysts for asymmetric catalysis and may facilitate the design of more redox-active crystalline organic polymers for electrochemical enantioselective processes.

Palladium-Catalyzed Electrooxidative Double C-H Arylation

The electrochemical transition metal-catalyzed cross-dehydrogenative reaction has emerged as a promising platform to achieve a sustainable and atom-economic organic synthesis that avoids hazardous oxidants and minimizes undesired byproducts and circuitous functional group operations. However, a poor mechanistic understanding still prevents the widespread adoption of this strategy. In this regard, we herein present an electrochemical palladium-catalyzed oxidative coupling strategy to access biaryls in the absence of a stoichiometric chemical oxidant. The robust palladaelectrocatalysis considerably suppresses the occurrence of homocoupling and oxygenation, being compatible even with electron-deficient arenes. Late-stage functionalization and Boscalid precursor synthesis further highlighted the practical importance of our electrolysis. Remarkably, mechanistic studies including the evaluation of the reaction order of each component by variable time normalization analysis (VTNA) and initial rate analysis, H/D exchange experiment, kinetic isotope effect, and stoichiometric organometallic experiments provided strong support for the involvement of transmetalation between two organopalladium complexes in the turnover limiting step. Therefore, matching the concentrations or lifetimes of two distinct organopalladium intermediates is revealed to be a pivot to the success of electrooxidative catalysis. Moreover, the presence of cationic copper(II) seems to contribute to the stabilization of the palladium(0) catalyst instead of playing a role in the oxidation of the catalyst.

Catalytic Asymmetric Synthesis of N-N Biaryl Atropisomers

Atropisomers have emerged as important structural scaffolds in natural products, drug design, and asymmetric synthesis. Recently, N-N biaryl atropisomers have drawn increasing interest due to their unique structure and relatively stable axes. However, its asymmetric synthesis remains scarce compared to its well-developed C-C biaryl analogs. In this concept, we summarize the asymmetric synthesis of N-N biaryl atropisomers including N-N pyrrole-pyrrole, N-N pyrrole-indole, N-N indole-indole, and N-N indole-carbazole, during which a series synthetic strategies are highlighted. Also, a synthetic evolution is briefly reviewed and an outlook of N-N biaryl atropisomers synthesis is offered.

Rhodium-Catalyzed Two-Fold, Regioselective and Enantioselective C-H Activation: an Efficient Strategy to Chiral Single-Benzene-Based Fluorophores

A Rh-catalyzed two-fold, regioselective and enantioselective C-H activation via chiral transient directing group strategy has been demonstrated in moderate to good yields with commendable enantioselectivities. The newly synthesized chiral fluorophores exhibit favorable photophysical properties, including large Stokes shifts, good fluorescence quantum yields, aggregation-induced emission in aqueous solution, and intense emission and circularly polarized luminescence in the solid state, indicating great potential applications as chiral fluorescent probes or optoelectronic materials.

Chiral Transient Ligand Enabled Enantioselective Synthesis of Atropisomers Decorated with Unactivated Olefins via a Palladium-Catalyzed C-H Olefination

Herein, atroposelective synthesis of axially chiral biaryls with unactivated olefins by a palladium-catalyzed C-H olefination using a chiral transient directing group strategy has been disclosed. This protocol is well compatible with a variety of biaryl-2-aldehydes as well as various olefins such as allyl sulfonamides and allyl sulfones to provide the atroposelective olefinated products in synthetically useful yields with excellent enantioselectivities up to >99% ee. In addition, a wide number of axially chiral biaryl alcohols were synthesized by the simple diversification of the products in excellent enantioselectivity.

Cu-catalyzed asymmetric regiodivergent electrosynthesis and its application in the enantioselective total synthesis of (-)-fumimycin

Quaternary amino acids are one of the essential building blocks and precursors of medicinally important compounds. Various synthetic strategies towards their synthesis have been reported. On the other hand, developing core-structure-oriented cross-dehydrogenative coupling (CDC) reactions, is a largely unsolved problem. Herein, we describe a copper-catalyzed regiodivergent electrochemical CDC reaction of Schiff bases and commercially available hydroquinones to obtain three classes of chiral quaternary amino acid derivatives for the efficient assembly of complex scaffolds with excellent stereocontrol. The electrochemical anodic oxidation process with slow releasing of quinones serves as an internal syringe pump and provides high levels of reaction efficiency and enantiomeric control. The utility of this strategy is highlighted through the synthetic utility in the asymmetric total synthesis of (-)-fumimycin.

Parallel paired electrolysis-enabled asymmetric catalysis: simultaneous synthesis of aldehydes/aryl bromides and chiral alcohols

Metal-catalyzed asymmetric electro-reductive couplings have emerged as a powerful tool for organic synthesis, wherein a sacrificial anode is typically required. Herein, a parallel paired electrolysis (PPE)-enabled asymmetric catalysis has been developed, and the alcohols and ketones could be simultaneously converted to the corresponding aldehydes and chiral tertiary alcohols with high yields and enantioselectivity in an undivided cell. Additionally, this Ni-catalyzed asymmetric reductive coupling can well match the anodic oxidative C-H bond bromination of (hetero)arenes. This protocol opens an alternative avenue for organic synthesis.

C-N Axially Chiral Heterobiaryl Isoquinolinone Skeletons Construction via Cobalt-Catalyzed Atroposelective C-H Activation/Annulation

Herein, the atroposelective construction of isoquinolinones bearing a C-N chiral axis has been successfully developed via a Co-catalyzed C-H bond activation and annulation process. This conversion can be effectively carried out in an environmentally friendly oxygen atmosphere to generate the target C-N axially chiral frameworks with excellent reactivities and enantioselectivities (up to >99% ee) in the absence of any additives. Additionally, the current protocol has proved to be an alternative approach for the C-N axial architectures fabrication under electrochemical conditions for cobalt/Salox catalysis, and this strategy allowed the efficient and atom-economical synthesis of various axially chiral isoquinolinones under mild reaction conditions.

Enantioselective organocatalytic synthesis of axially chiral aldehyde-containing styrenes via SNAr reaction-guided dynamic kinetic resolution

The precise and efficient construction of axially chiral scaffolds, particularly toward the aryl-alkene atropoisomers with impeccably full enantiocontrol and highly structural diversity, remains greatly challenging. Herein, we disclose an organocatalytic asymmetric nucleophilic aromatic substitution (SNAr) reaction of aldehyde-substituted styrenes involving a dynamic kinetic resolution process via a hemiacetal intermediate, offering a novel and facile way to significant axial styrene scaffolds. Upon treatment of the aldehyde-containing styrenes bearing (o-hydroxyl)aryl unit with commonly available fluoroarenes in the presence of chiral peptide-phosphonium salts, the SNAr reaction via an exquisite bridged biaryl lactol intermediate undergoes smoothly to furnish a series of axially chiral aldehyde-containing styrenes decorated with various functionalities and bioactive fragments in high stereoselectivities (up to >99% ee) and complete E/Z selectivities. These resulting structural motifs are important building blocks for the preparation of diverse functionalized axial styrenes, which have great potential as efficient and privileged chiral ligands/catalysts in asymmetric synthesis.

Iridium(I)-Catalyzed Atroposelective Alkenylation of Heterobiaryls with Terminal Alkynes

Herein we report an iridium(I)-catalyzed atroposelective alkenylation of isoquinoline-derived heterobiaryls with terminal alkynes. In the presence of a cationic iridium(I) catalyst with (R)-SEGPHOS as the chiral ligand, this atom-economical alkenylation protocol allows the rapid construction of a series of axially chiral alkenylated heterobiaryls in moderate to good yields with good to high enantioselectivities.

Cobaltaelectro-Catalyzed C-H Annulation with Allenes for Atropochiral and P-Stereogenic Compounds: Late-Stage Diversification and Continuous Flow Scale-Up

The 3d metallaelectro-catalyzed C-H activation has been identified as an increasingly viable strategy to access valuable organic molecules in a resource-economic fashion under exceedingly mild reaction conditions. However, the development of enantioselective 3d metallaelectro-catalyzed C-H activation is very challenging and in its infancy. Here, we disclose the merger of cobaltaelectro-catalyzed C-H activation with asymmetric catalysis for the highly enantioselective annulation of allenes. A broad range of C-N axially chiral and P-stereogenic compounds were thereby obtained in good yields of up to 98% with high enantioselectivities of up to >99% ee. The practicality of this approach was demonstrated by the diversification of complex bioactive compounds and drug molecules as well as decagram scale enantioselective electrocatalysis in continuous flow.

Electrocatalyzed direct arene alkenylations without directing groups for selective late-stage drug diversification

Electrooxidation has emerged as an increasingly viable platform in molecular syntheses that can avoid stoichiometric chemical redox agents. Despite major progress in electrochemical C-H activations, these arene functionalizations generally require directing groups to enable the C-H activation. The installation and removal of these directing groups call for additional synthesis steps, which jeopardizes the inherent efficacy of the electrochemical C-H activation approach, leading to undesired waste with reduced step and atom economy. In sharp contrast, herein we present palladium-electrochemical C-H olefinations of simple arenes devoid of exogenous directing groups. The robust electrocatalysis protocol proved amenable to a wide range of both electron-rich and electron-deficient arenes under exceedingly mild reaction conditions, avoiding chemical oxidants. This study points to an interesting approach of two electrochemical transformations for the success of outstanding levels of position-selectivities in direct olefinations of electron-rich anisoles. A physical organic parameter-based machine learning model was developed to predict position-selectivity in electrochemical C-H olefinations. Furthermore, late-stage functionalizations set the stage for the direct C-H olefinations of structurally complex pharmaceutically relevant compounds, thereby avoiding protection and directing group manipulations.

Aggregation-Induced Catalysis: Asymmetric Catalysis with Chiral Aggregates

So far, there have been 4 methods to control chirality including the use of chiral auxiliaries, reagents, solvents, and catalysts documented in literature and textbooks. Among them, asymmetric catalysts are normally divided into homogeneous and heterogeneous catalysis. In this report, we present a new type of asymmetric control-asymmetric catalysis via chiral aggregates that would not belong to the above categories. This new strategy is represented by catalytic asymmetric dihydroxylation reaction of olefins in which chiral ligands are aggregated by taking advantage of typical aggregation-induced emission systems containing tetrahydrofuran and H₂O cosolvents. It was proven that the chiral induction can be enhanced from er of 78:22 to 97:3 simply by changing the ratios of these 2 cosolvents. The formation of chiral aggregates of asymmetric dihydroxylation ligands, (DHQD)₂PHAL and (DHQ)₂PHAL, has been proven by aggregation-induced emission and a new analytical tool-aggregation-induced polarization established by our laboratory. In the meanwhile, chiral aggregates were found to be formed either by adding NaCl into tetrahydrofuran/H₂O systems or by increasing concentrations of chiral ligands. The present strategy also showed promising reverse control of enantioselectivity in the Diels-Alder reaction. This work is anticipated to be extended broadly to general catalysis, especially to asymmetric catalysis in the future.

A C-H activation-based enantioselective synthesis of lower carbo[n]helicenes

The three-dimensional structure of carbohelicenes has fascinated generations of molecular chemists and has been exploited in a wide range of applications. Their strong circularly polarized luminescence has attracted considerable attention in recent years due to promising applications in new optical materials. Although the enantioselective synthesis of fused carbo- and heterohelicenes has been achieved, a direct catalytic enantioselective method allowing the synthesis of lower, non-fused carbo[n]helicenes (n = 4-6) is still lacking. We report here that Pd-catalysed enantioselective C-H arylation in the presence of a unique bifunctional phosphine-carboxylate ligand provides a simple and general access to these lower carbo[n]helicenes. Computational mechanistic studies indicate that both the C-H activation and reductive elimination steps contribute to the overall enantioselectivity. The observed enantio-induction seems to arise from a combination of non-covalent interactions and steric repulsion between the substrate and ligand during the two key reductive elimination steps. The photophysical and chiroptical properties of the synthesized scalemic [n]helicenes have been systematically studied.

Desymmetrization of Prochiral N-Pyrazolyl Maleimides via Organocatalyzed Asymmetric Michael Addition with Pyrazolones: Construction of Tri-N-Heterocyclic Scaffolds Bearing Both Central and Axial Chirality

The desymmetrization of N-pyrazolyl maleimides was realized through an asymmetric Michael addition by using pyrazolones under mild conditions, leading to the formation of a tri-N-heterocyclic pyrazole-succinimide-pyrazolone assembly in high yields with excellent enantioselectivities (up to 99% yield, up to 99% ee). The use of a quinine-derived thiourea catalyst was essential for achieving stereocontrol of the vicinal quaternary-tertiary stereocenters together with the C-N chiral axis. Salient features of this protocol included a broad substrate scope, atom economy, mild conditions and simple operation. Moreover, a gram-scale experiment and derivatization of the product further illustrated the practicability and potential application value of this methodology.

Helicity-modulated remote C-H functionalization

Remote C-H functionalization is highly important for the conversion and utilization of arenes, but the conventional routes are comprehensively developed with the assistance of transition metal catalysts or templates. We report a facile metal/template-free electrochemical strategy for remote C-H functionalization in a helical system, where aromatic or aliphatic hydrogen act as a directing group to promote the alkoxylation at the opposite site of the helical skeleton by generating a unique helical "back-biting" environment. Such helicity-modulated C-H functionalization is prevalent for carbo[n]helicenes (n = 6 to 9, primitive or substituted) and hetero[6]helicenes and also occurs when the aryl hydrogen on the first position is replaced by a methyl group or a phenyl group. Thus, the relatively inert helicene skeleton can be precisely furnished with a rich array of alkoxy pendants with tunable functional moieties. Notably, the selective decoration of a methoxy group on N-methylated aza[6]helicene close or distant to the nitrogen atom leads to distinct luminescence variation upon changing the solvents.