Dearomative Ring-Opening of N-Fused Heteroarenes: Access to Tetrasubstituted Alkenes and Ketimines

We report a novel and efficient strategy for constructing tetrasubstituted alkenes and α-iminonitriles from 3-aminoindolizines and 3-aminoimidazo[1,2-a]pyridines. This approach involves a dearomative ring-opening of N-fused heteroaromatic amines coupled to a DDQ-mediated oxidative process under mild, metal-free conditions. The methodology demonstrates broad substrate scope, excellent functional group tolerance, and scalability, offering a versatile platform for synthesizing complex alkenes and nitrile-containing frameworks.

Palladium-Catalyzed Domino Heck/Decarboxylative Cyanomethylation of Indoles and Alkenes with Cyanoacetate Salts

A palladium-catalyzed reaction of indoles with cyanoacetate salts enables the synthesis of 2,6-disubstituted indolines via tandem dearomatization/decarboxylative cyanomethylation. Remarkably, this is the first example of indole difunctionalization at the C2 and C6 positions. Moreover, this methodology extends to the palladium-catalyzed cyclization/decarboxylative cyanomethylation of aryl halide-tethered alkenes.

Visible light-mediated dearomative spirocyclization/imination of nonactivated arenes through energy transfer catalysis

Aromatic compounds serve as key feedstocks in the chemical industry, typically undergoing functionalization or full reduction. However, partial reduction via dearomative sequences remains underexplored despite its potential to rapidly generate complex three-dimensional scaffolds and the existing dearomative strategies often require metal-mediated multistep processes or suffer from limited applicability. Herein, a photocatalytic radical cascade approach enabling dearomative difunctionalization through selective spirocyclization/imination of nonactivated arenes is reported. The method employs bifunctional oxime esters and carbonates to introduce multiple functional groups in a single step, forming spirocyclic motifs and iminyl functionalities via N-O bond cleavage, hydrogen-atom transfer, radical addition, spirocyclization, and radical-radical cross-coupling. The reaction constructs up to four bonds (C-O, C-C, C-N) from simple starting materials. Its broad applicability is demonstrated on various substrates, including pharmaceuticals, and it is compatible with scale-up under flow conditions, offering a streamlined approach to synthesizing highly decorated three-dimensional frameworks.

A stepwise dearomatization/nitration/enantioselective homoenolate reaction of quinolines to construct C3-nitro-substituted tetrahydroquinolines

Herein, we describe a stepwise 1,2-reductive dearomatization/selective C3-nitration of quinoline and a subsequent catalytic enantioselective homoenolate addition reaction using a NHC catalyst strategy to construct N-acetyl 3,4-disubstituted tetrahydroquinoline in good yields with remarkably high diastereo- and enantioselectivities (dr >99 : 1, ee up to >99%). An efficient metal- and base-free method for 3-nitroquinoline synthesis from readily accessible quinoline has also been realized.

Highly Diastereoselective Synthesis of Oxindole-Bearing Pyrroloindoline via Gold Catalyzed Carbophilic Carbene Transfer Reaction

A new type of gold catalyzed intermolecular dearomative cyclization reaction between diazo oxindole and tryptamine has been developed by utilizing the combination of L3AuCl/Ag3PO4 (L3=hexamethyl phosphane triamine) as the catalyst. This method allows for the facile preparation of a series of C-3-oxindole fused pyrroloindoline products in moderate to good yields with high diastereoselectivities. A plausible reaction mechanism, involving a cascade process of regioselective nucleophilic addition of the carbophilic gold carbenoid intermediate onto tryptamine, followed by an intramolecular cyclization, has been proposed, in which, the high diastereoselectivity is attributed to a preferred transition state. Moreover, three oxindole-bearing indolo[2,3-b] quinoline derivatives were synthesized through dearomative cyclization of homotryptamine derivative 4a with the respective 3-diazoindolin-2-one substrates using a similar strategy. A gram-scale experiment successfully yielded 1.95 g of 3 aa in 85 % yield with a diastereomeric ratio (dr) of 10.4/1, ultimately enabling a five-step synthesis of the natural product (±)-folicanthine.

Enantioselective Dearomative [2π + 2σ] Photocycloaddition of Naphthalene Derivatives with Bicyclo[1.1.0]butanes Enabled by Gd(III) Catalysis

The cycloaddition reactions of bicyclo[1.1.0]butanes with alkenes, imines, nitrones, or aziridines have served as an efficient platform to create conformationally restricted saturated bicyclic scaffolds. However, the use of readily available aromatics in such reactions, especially in an asymmetric manner, remains underexplored. Herein, we report a highly regio- and enantioselective dearomative [2π + 2σ] photocycloaddition reaction between naphthalene derivatives and bicyclo[1.1.0]butanes, enabled by Gd(III) catalysis. Bicyclo[1.1.0]butanes and naphthalenes adorned with a diverse array of functional groups are well-tolerated under mild conditions, affording enantioenriched pharmaceutically important bicyclo[2.1.1]hexanes in 30-96% yields with 81-93% ee and 12:1 → >20:1 rr. The synthetic versatility of this reaction is further demonstrated by the facile removal of directing group and derivatizations of the dearomatized product. UV-vis absorption spectroscopy studies suggest the involvement of an excited naphthalene species in the reaction process.

Dearomative Skeletal Editing of Benzenoids via Diradical

Dearomative skeletal editing of benzenoids represents a promising yet challenging strategy for the rapid construction of high-value carbon frameworks from readily accessible starting materials. Büchner reaction is a unique type of expansive skeletal editing that transforms benzenoids into functionalized cycloheptatrienes. However, due to challenges in compatibility and selectivity, achieving seamless integration of this reaction with dearomative cycloaddition within a unified system remains undeveloped. Here, we demonstrated an energy-transfer-induced intermolecular dearomative skeletal editing reaction of benzenoids with a range of electronically diverse alkynes. This protocol employed N-acylimines as diradical precursors to efficiently construct various structurally diverse polycyclic frameworks in high chemo-, regio-, and diastereoselectivities that have been previously inaccessible. The challenges related to general reactivity and selectivity issues were circumvented through the smooth merging of photoinduced skeletal editing with dearomative cycloaddition. Experimental and computational studies were performed to support the diradical mechanism and interpret the origins of the observed chemo-, regio-, and diastereoselectivities.

Dearomative C2-borylation of indoles

The dearomative borylation of indoles is challenging and typically requires transition metal catalysts, strong bases, or harsh conditions. We report the metal- and base-free C2-borylation of indoles using bis(1-methyl-ortho-carboranyl)borane as an electrophilic borylating reagent to generate borylated indolenium species under mild conditions.

Progress in Double Dearomatization Reactions

Dearomatization reactions are among the most straightforward and efficient methods for creating sp3-rich cyclic systems from simple, readily available arenes. These reactions have been widely applied in the total synthesis of natural products, medicinal chemistry, and material sciences. The fruitful development of dearomatization strategies and methodologies targeting single aromatic substrate over the past decades has paved the way for more sophisticated multiple dearomatization processes, which offer greater advantages in constructing molecular complexity. Double dearomatization reactions have made significant pioneering strides in recent years. This review will provide an overview of the strategies and detailed examples of multiple dearomatization reactions involving various aromatic compounds, along with a discussion of the related mechanisms and the major challenges that remain in this intriguing yet formidable field.

CuI-Catalyzed Dearomatization/Peroxidation/Cyclization Cascade of Pyrrole-Tethered Indoles

A mild CuI-catalyzed dearomatization/peroxidation/cyclization cascade of pyrrole-tethered indoles has been reached, providing peroxide-incorporated indolizino[8,7-b]indole derivatives in acceptable to good yields (46-76%). Dehydrogenated peroxide can be obtained by the use of a FeCl3/TBHP (tBuOOH)/2,2,2-trifluoroethanol (TFE) system at 50 °C.

FeCl3-catalyzed oxidative diselenylation of pyrrole-tethered indoles

A mild and efficient FeCl3-catalyzed oxidative diselenylation of pyrrole-tethered indoles has been achieved by using RSeSeR as the source of selenium and m-chloroperoxybenzoic acid (mCPBA) as the oxidant (17-70% yields). In addition, this selenylation reaction system can be expanded to the functionalization of tryptophan derivatives and melatonin at the C-2 position of the indole moiety (55-58% yields).

Synthesis, structure, ionochromic and cytotoxic properties of new 2-(indolin-2-yl)-1,3-tropolones

The acid-catalyzed reaction of benzo[e(g)] derivatives of 2,3,3-trimethylindolenines with o-chloranil leads to new 2-(benzo[e(g)]indolin-2-yl)-5,6,7-trichloro-1,3-tropolones and 2-(benzo[e(g)]indolin-2-yl)-4,5,6,7-tetrachloro-1,3-tropolones. Based on the results of PBE0/6-311+G(d,p) calculations, the structural and energetic characteristics of the tautomeric forms of the obtained 1,3-tropolones were determined. The structure of 2-(3,3-dimethyl-3H-benzo[g]indolin-2-yl)-5,6,7-trichloro-1,3-tropolone was determined by X-ray diffraction analysis. The compounds obtained are capable of switching emission at 420-440 nm and 476-530 nm upon successive exposure to CN- and Hg2+ ions in an acetonitrile solution. 2-(1,1-Dimethyl-1H-benzo[e]indolin-2-yl)-5,6,7-trichloro-1,3-tropolone exhibited high in vitro cytotoxic activity against A431 skin cancer and H1299 lung cancer cell lines.

Rhodium-Catalyzed Homogeneous Asymmetric Hydrogenation of Naphthol Derivatives

Due to their strong aromaticity and difficulties in chemo-, regio-, and enantioselectivity control, asymmetric hydrogenation of naphthol derivatives to 1,2,3,4-tetrahydronaphthols has remained a long-standing challenge. Herein, we report the first example of homogeneous asymmetric hydrogenation of naphthol derivatives catalyzed by tethered rhodium-diamine catalysts, affording a wide array of optically pure 1,2,3,4-tetrahydronaphthols in high yields with excellent regio-, chemo-, and enantioselectivities (up to 98% yield and >99% ee). Mechanistic studies with experimental and computational approaches reveal that fluorinated solvent 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) plays vital roles in the control of reactivity and selectivity, and 1-naphthol is reduced via a cascade reaction pathway, including dearomative tautomerization, 1,4-hydride addition, and 1,2-hydride addition in sequence. A novel synergistic activation mode was proposed in which HFIP assists a synergistic activation of both the hydrogen molecule and naphthol in the presence of a base, and the in situ-generated fleeting keto tautomer is immediately trapped and reduced by the Rh(III)-H species before it escapes from the solvent cage. This protocol provides a straightforward and practical pathway for the synthesis of key intermediates for several chiral drugs. Particularly, optically pure Nadolol, a drug for the treatment of hypertension, angina pectoris, congestive heart failure, and certain arrhythmias, is enantioselectively synthesized for the first time.

Reaction strategies for the meta-selective functionalization of pyridine through dearomatization

The pyridine moiety is a crucial structural component in various pharmaceuticals. While the direct ortho- and para-functionalization of pyridines is relatively straightforward, the meta-selective C-H functionalization remains a significant challenge. This review highlights dearomatization strategies as a key area of interest in expanding the application of meta-C-H functionalization of pyridines. Dearomatization enables the meta-functionalization through various catalytic methods that directly generate dearomatization products, and some products can be rearomatized back to pyridine derivatives. Furthermore, this article also covers the dearomatization of multiple positions of pyridine in the synthesis of polycyclic compounds. It offers a comprehensive overview of the latest advancements in dearomatization at different positions of pyridine, aiming to provide a valuable resource for researchers in this field. It also highlights the advantages and limitations of existing technologies, aiming to inform a broader audience about this important field and foster its future development.

Asymmetric dearomative single-atom skeletal editing of indoles and pyrroles

Heterocycle skeletal editing has recently emerged as a powerful tactic for achieving heterocycle-to-heterocycle transmutation without the need for multistep de novo heterocycle synthesis. However, the enantioselective skeletal editing of heteroarenes through single-atom logic remains challenging. Here we report the enantiodivergent dearomative skeletal editing of indoles and pyrroles via an asymmetric carbon-atom insertion, using trifluoromethyl N-triftosylhydrazones as carbene precursors. This strategy provides a straightforward methodology to access enantiomerically enriched six-membered N-heterocycles containing a trifluoromethylated quaternary stereocentre from planar N-heteroarenes. The synthetic utility of this enantiodivergent methodology was demonstrated by a broad evaluation of reaction scope, product derivatization and concise syntheses of drug analogues. Mechanistic studies reveal that the excellent asymmetric induction arises from the initial cyclopropanation step. The asymmetric single-atom insertion strategy is expected to have a broad impact on the field of single-atom skeletal editing and catalytic asymmetric dearomatization of aromatic compounds.

Electrochemical oxidative dearomatization of electron-deficient phenols using Br+/Br- catalysis

An electrochemical method for the oxidative dearomatization of electron-deficient phenols by employing tetrabutylammonium bromide as a mediator under aqueous biphasic conditions is reported. This approach represents a safer alternative to the use of stoichiometric chemical oxidants and enables oxidative dearomative spirolactonization and spiroetherification reactions. Compared to previous approaches based on direct electrolysis, this strategy expands the substrate scope to electron-deficient phenols. Cyclic-voltammetry analysis suggests that the bromide ions might be oxidized to Br2 or Br3- ions that are in equilibrium with the catalytically active hypobromite under aqueous conditions.

Organocatalyzed Enantioselective Double Dearomatization of Tricyclic Phenols and Alkoxybenzenes

To advance more efficient dearomatization approaches, we present herein an organocatalyzed asymmetric double dearomatization reaction of tricyclic phenols and alkoxybenzenes by leveraging a novel steric hindrance-regulated dearomatization strategy for nonfunctionalized phenols. This protocol allows the efficient synthesis of structurally complex polycyclic diketones with four tertiary carbon centers under mild conditions while also showcasing the potential of multiple dearomatizations for building intricate molecular frameworks from simple starting materials.

Organocatalytic Stereodivergent Dearomatization and N-Acylation of 2-Amino-3-subsituted Indoles

Organocatalytic chemo- and enantioselective reactions of 2-amino-3-subsituted indoles have been achieved for the first time. Via asymmetric allylic alkylation of Morita-Baylis-Hillman carbonates, organocatalytic enantioselective dearomatization of 2-amino-3-subsituted indoles afforded an array of enantioenriched 3,3-disubstituted indolin-2-imines bearing a quaternary carbon stereocenter in 34-79% yields with 61-91% ee. With Boc2O as reaction partner, the organocatalytic enantioselective N-acylation of 2-amino-3-subsituted indoles was established to furnish C-N axially chiral products in 22-98% yields with 73-92% ee.

Intermolecular Asymmetric Arylative Dearomatization of 1-Naphthols

Arylative dearomatization forms quaternary stereocenters in cyclic systems with the concomitant introduction of an aromatic ring. Pd-catalyzed arylative dearomatization, which uses conditions analogous to cross-coupling, has emerged as a powerful method in an intramolecular context. But translating this from intramolecular cyclizations to an intermolecular process has proven extremely challenging: examples are scarce, and those that exist have not been rendered enantioselective, despite the potential for broad application in medicinal chemistry and natural product synthesis. We describe a strategy that utilizes attractive interactions between the ligand and substrate to overcome this challenge and promote intermolecular, highly enantioselective arylative dearomatization of naphthols using a broad range of aryl bromide electrophiles. Crucial to success is the use of the readily accessed sulfonated chiral phosphine sSPhos, which we believe engages in attractive electrostatic interactions with the substrate. Not only does sSPhos control enantioselectivity but it also drastically accelerates the reaction, most likely by facilitating the challenging palladation step that initiates dearomatization.

Three-Component Synthesis of Multiply Functionalized 5,6-Dehydroisoquinuclidines through Dearomatization of Pyridine

A three-component synthesis of multiply functionalized 5,6-dehydroisoquinuclidines is described. After the formation of an N-alkylpyridinium salt, Grignard addition led to the formation of the corresponding 1,2-dihydropyridine bearing an alkyl, alkene, aryl, or alkynyl group. Subsequent Diels-Alder reaction with a dienophile provided functionalized dehydroisoquinuclidines in high yields (up to 93%) with endo selectivities (73:27 to >99:1). This reaction was applicable to the synthesis of an N-(4-methoxybenzyl)pyridinium salt, where the 4-methoxybenzyl group was switched to a benzyloxycarbonyl group after the formation of the dehydroisoquinuclidine.

A metalloenzyme platform for catalytic asymmetric radical dearomatization

Catalytic asymmetric dearomatization represents a powerful means to convert flat aromatic compounds into stereochemically well-defined three-dimensional molecular scaffolds. Using new-to-nature metalloredox biocatalysis, we describe an enzymatic strategy for catalytic asymmetric dearomatization via a challenging radical mechanism that has eluded small-molecule catalysts. Enabled by directed evolution, new-to-nature radical dearomatases P450rad1-P450rad5 facilitated asymmetric dearomatization of a broad spectrum of aromatic substrates, including indoles, pyrroles and phenols, allowing both enantioconvergent and enantiodivergent radical dearomatization reactions to be accomplished with excellent enzymatic control. Computational studies revealed the importance of additional hydrogen bonding interactions between the engineered metalloenzyme and the reactive intermediate in enhancing enzymatic activity and enantiocontrol. Furthermore, designer non-ionic surfactants were found to significantly accelerate this biotransformation, providing an alternative means to promote otherwise sluggish new-to-nature biotransformations. Together, this evolvable metalloenzyme platform opens up new avenues to advance challenging catalytic asymmetric dearomatization processes involving free radical intermediates.

Azocarboxamide-enabled enantioselective regiodivergent unsymmetrical 1,2-diaminations

Enantioenriched unsymmetrical vicinal diamines are important basic structural motifs. While catalytic asymmetric intermolecular 1,2-diamination of carbon-carbon double bonds represents the most straightforward approach for preparing enantioenriched vicinal-diamine-containing heterocycles, these reactions are often limited to the installation of undifferentiated amino functionalities through metal catalysis and/or the use of stoichiometric amounts of oxidants. Here, we report organocatalytic enantioselective unsymmetrical 1,2-diaminations based on the rational design of a bifunctional 1,2-diamination reagent, namely, azocarboxamides (ACAs). Under the catalysis of chiral phosphoric acid, unsymmetrical 1,2-diaminations of ACAs with various electron-rich double bonds readily occur in a regiodivergent manner. Indoles prefer dual hydrogen-bonding mode to give dearomative (4 + 2) products, and 3-vinylindoles and azlactones are inclined to undergo unsymmetrical 1,2-diamination via the (3 + 2) process. DFT calculations are performed to reveal the reaction mechanism and the origin of the regio- and enantioselectivity. Guided by computational design, we are able to reverse the regioselectivity of the dearomative unsymmetrical 1,2-diamination of indoles using Lewis acid catalysis.

Catalytic kinetic resolution of helical polycyclic phenols via an organocatalyzed enantioselective dearomative amination reaction

Despite the considerable potential applications for helically chiral molecules across various sectors, their catalytic asymmetric synthesis remains nascent and has seen very limited advancement compared to that of central and axial chiral compounds, primarily owing to the scarcity of available starting materials and the immense challenges associated with achieving stereochemical control. Herein, we report an innovative approach to the facile synthesis and catalytic kinetic resolution of uniquely structured and stereochemically complex helical polycyclic phenols by using a steric hindrance-regulated enantioselective dearomative amination reaction. The distinguished aspects of this method include the exceptional stability of the dearomatized products and impressive versatility of the recovered substrates in the construction of enantioenriched helical frameworks. This work showcases that the strategic incorporation of appropriate steric groups near the reaction site of an electron-rich aromatic compound can indeed enable an interrupted Friedel-Crafts reaction, thus opening an alternate avenue for the study of dearomatization in nonfunctionalized arenes.

Palladium-Catalyzed Dearomative Heck/C(sp2)-H Activation/Decarboxylative Cyclization of C2-Tethered Indoles

Until now, palladium-catalyzed dearomative Heck reactions of indoles were largely limited to β-H elimination and nucleophilic capture of the transient alkyl-Pd(II) species. Herein, we disclose a novel palladium-catalyzed dearomative Heck/C(sp2)-H activation/decarboxylative cyclization of C2-tethered indoles. In this protocol, the alkyl-Pd(II) species formed by dearomatization of C2-tethered indoles is not terminated by common β-H elimination or nucleophilic capture, but rather generates C,C-palladacycle via C-H activation. The latter is intercepted by α-bromoacrylic acids to produce pentacyclic and heptacyclic fused indolines.

Construction of fused heterocycles by visible-light induced dearomatization of nonactivated arenes

A diverse array of fused [6-6-5] tricyclic heterocycles has been synthesized via the dimerization and dearomative cyclization of benzene derivatives under visible light irradiation. The initiation of the cascade process is likely from aryloxy radicals, engendered through proton-coupled electron transfer by the photoexcited vinylidene ortho-quinone methide (VQM) and a Brønsted base.

Enantioselective Organocatalyzed Cascade Dearomatizing Spirocycloaddition Reactions of Indole-Ynones

An intramolecular organocatalytic cascade dearomatizing spirocycloaddition reaction of indole-ynone compounds containing O-silyl-naphthol substituents has been developed with the use of a chiral bifunctional thiourea. This process was able to provide various structurally diverse polycyclic spiroindolines in high yields (up to 98%) with excellent stereoselectivities (>20:1 dr, up to 98% ee) involving the formation of carbonylvinylidene ortho-quinone methide intermediates.

Dearomative Construction of 2D/3D Frameworks from Quinolines via Nucleophilic Addition/Borate-Mediated Photocycloaddition

Dearomative construction of multiply-fused 2D/3D frameworks, composed of aromatic two-dimensional (2D) rings and saturated three-dimensional (3D) rings, from readily available quinolines has greatly contributed to drug discovery. However, dearomative cycloadditions of quinolines in the presence of photocatalysts usually afford 5,6,7,8-tetrahydroquinoline (THQ)-based polycycles, and dearomative access to 1,2,3,4-THQ-based structures remains limited. Herein, we present a chemo-, regio-, diastereo-, and enantioselective dearomative transformation of quinolines into 1,2,3,4-THQ-based 6-6-4-membered rings without any catalyst, through a combination of nucleophilic addition and borate-mediated [2+2] photocycloaddition. Detailed mechanistic studies revealed that the photoexcited borate complex, generated from quinoline, organolithium, and HB(pin), accelerates the cycloaddition and suppresses the rearomatization that usually occurs in conventional photocycloaddition. Based on our mechanistic analysis, we also developed further photoinduced cycloadditions affording other types of 2D/3D frameworks from isoquinoline and phenanthrene.

Rhodium-Catalyzed Asymmetric Cyclopropanation of Indoles with N-Triftosylhydrazones

Herein we report a general rhodium-catalyzed asymmetric intermolecular dearomative cyclopropanation of indoles using trifluoromethyl N-triftosylhydrazones as carbene precursors. The reaction enables the rapid construction of diverse cyclopropane-fused indolines bearing a trifluoromethylated quaternary stereocenter with high enantioselectivity (up to 99 % ee). This mild method exhibits broad substrate scope, tolerating various functional groups, and can even be utilized for the late-stage diversification of complex bioactive molecules. DFT calculations suggest that the formation of a key zwitterionic intermediate is responsible for the chiral induction. Overall, this approach opens up new possibilities for asymmetric cyclopropanation of challenging aromatic heterocyclic compounds.

Asymmetric Dearomatization of Indoles through Cobalt-Catalyzed Enantioselective C-H Functionalization Enabled by Photocatalysis

Photocatalysis holds a pivotal position in modern organic synthesis, capable of inducing novel reactivities under mild and environmentally friendly reaction conditions. However, the merger of photocatalysis and transition-metal-catalyzed asymmetric C-H activation as an efficient and sustainable method for the construction of chiral molecules remains elusive and challenging. Herein, we develop a cobalt-catalyzed enantioselective C-H activation reaction enabled by visible-light photoredox catalysis, providing a synergistic catalytic strategy for the asymmetric dearomatization of indoles with high levels of enantioselectivity (96 % to >99 % ee). Mechanistic studies indicate that the excited photocatalyst was quenched by divalent cobalt species in the presence of Salox ligand, leading to the formation of catalytically active chiral Co(III) complex. Moreover, stoichiometric reactions of cobaltacycle intermediate with indole suggest that the irradiation of visible light also play a critical role in the dearomatization step.

Electrocatalytic reductive deuteration of arenes and heteroarenes

The incorporation of deuterium in organic molecules has widespread applications in medicinal chemistry and materials science1,2. For example, the deuterated drugs austedo3, donafenib4 and sotyktu5 have been recently approved. There are various methods for the synthesis of deuterated compounds with high deuterium incorporation6. However, the reductive deuteration of aromatic hydrocarbons-ubiquitous chemical feedstocks-to saturated cyclic compounds has rarely been achieved. Here we describe a scalable and general electrocatalytic method for the reductive deuteration and deuterodefluorination of (hetero)arenes using a prepared nitrogen-doped electrode and deuterium oxide (D2O), giving perdeuterated and saturated deuterocarbon products. This protocol has been successfully applied to the synthesis of 13 highly deuterated drug molecules. Mechanistic investigations suggest that the ruthenium-deuterium species, generated by electrolysis of D2O in the presence of a nitrogen-doped ruthenium electrode, are key intermediates that directly reduce aromatic compounds. This quick and cost-effective methodology for the preparation of highly deuterium-labelled saturated (hetero)cyclic compounds could be applied in drug development and metabolism studies.

Catalyst-Free Dearomative Allylboration of Ketones with Benzo[b]thiophenylmethyl Boronic Acids

A novel approach to the dearomative allylboration of ketones with benzo[b]thiophenylmethyl boronic acids has been developed. By leveraging the inherent reactivity of the boronic acid unit, this process occurs under mild reaction conditions without the need for a catalyst, leading to the efficient formation of homoallylic tertiary alcohols accompanied by the construction of three-dimensional sulfur-containing alicyclic scaffolds in high yields with excellent stereoselectivities.

Chiral Brønsted Acid-Catalyzed Intramolecular Asymmetric Dearomatization Reaction of Indoles with Cyclobutanones via Cascade Friedel-Crafts/Semipinacol Rearrangement

The highly efficient synthesis of chiral indolines fused with an azabicyclo[2.2.1]heptanone moiety is achieved by an asymmetric dearomatization reaction of indoles with cyclobutanones. A new chiral imidodiphosphorimidate (IDPi) catalyst is synthesized and exhibits extraordinary activity in promoting a cascade Friedel-Crafts/semipinacol rearrangement. Target molecules are prepared in good yields (up to 95%) with excellent enantioselectivity (up to 98% ee) with operational convenience. Combined experimental and computational studies provide detailed mechanistic insights into the energy landscape and origin of the stereochemical induction of the reaction.

Oxidative Dearomative Coupling of Electron-Deficient Arenols Using Hypohalite Catalysis

We developed performant in situ hypohalite, especially hypobromite, catalysis for the oxidative dearomatization of low-reactivity electron-deficient arenols. The reaction scope encompasses inter- and intramolecular oxidative dearomative C-O, C-N, and C-C coupling reactions. Notably, using a chiral ammonium countercation, we achieved enantioselective hypobromite catalysis for oxidative dearomative coupling reactions. Mechanistic studies revealed that the reaction mechanisms might differ depending on the halide identity.

Catalytic Asymmetric Dearomative [2 + 2] Photocycloaddition/Ring-Expansion Sequence of Indoles with Diversified Alkenes

Developing novel strategies for catalytic asymmetric dearomatization (CADA) reactions is highly valuable. Visible light-mediated photocatalysis is demonstrated to be a powerful tool to activate aromatic compounds for further synthetic transformations. Herein, a catalytic asymmetric dearomative [2 + 2] photocycloaddition/ring-expansion sequence of indoles with simple alkenes was reported, providing a facile access to enantioenriched cyclopenta[b]indoles with good to high yields and enantioselectivities by means of chiral lanthanide photocatalysis. This protocol exhibited a broad substrate scope and good functional group tolerance, as well as potential applications in the synthesis of bioactive molecules. Mechanistic studies, including control experiments, UV-vis absorption spectroscopy, emission spectroscopy, and DFT calculations, were carried out, shedding insights into the reaction mechanism and the origin of enantioselectivity.

Electrophile-Arene Affinity: An Energy Scale for Evaluating the Thermodynamics of Electrophilic Dearomatization Reactions

Rational design and development of organic reactions are lofty goals in synthetic chemistry. Quantitative description of the properties of molecules and reactions by physical organic parameters plays an important role in this regard. In this Article, we report an energy scale, namely, electrophile-arene affinity (EAA), for evaluating the thermodynamics of electrophilic dearomatization reactions, a class of important transformations that can rapidly build up molecular complexity and structural diversity by converting planar aromatic compounds into three-dimensional cyclic molecules. The acquisition of EAA data can be readily achieved by theoretically calculating the enthalpy changes (ΔH) of the hypothetical reactions of various (cationic) electrophiles with aromatic systems (taking the 1-methylnaphthalen-2-olate ion as an example in this study). Linear correlations are found between the calculated ΔH values and established physical organic parameters such as the percentage of buried volume %VBur (steric effect), Hammett's σ or Brown's σ+ (electronic effect), and Mayr's E (reaction kinetics). Careful analysis of the ΔH values leads to the rational design of a dearomative alkynylation reaction using alkynyl hypervalent iodonium reagents as the electrophiles.

Synthesis of C(3) SCF3-Substituted Pyrrolidinoindoline by PIII/PV Redox Catalysis Using CF3SO2Cl as Electrophilic CF3S Reagent

This work reports a method for the catalytic synthesis of C(3) SCF3-substituted pyrrolidinindoline using a small-ring organophosphorus-based catalyst and a hydrosilane reductant, with trifluoromethanesulfonyl chloride as the electrophilic SCF3 reagent. This method can drive the conversion of tryptamine to the C(3) SCF3-substituted pyrrolidine indoline. The readily available, inexpensive trifluoromethanesulfonyl chloride could be activated as an electrophilic SCF3 source by PIII/PV redox catalysis and could efficiently participate in the reaction of tryptamines, thus providing various substituted C(3) SCF3-substituted pyrrolidinoindoline in moderate to excellent yields. This presented strategy features a broad substrate scope, and the structure has value for in-depth research.

Umpolung-Enabled Divergent Dearomative Carbonylations

Although dearomative functionalizations enable the direct conversion of flat aromatics into precious three-dimensional architectures, the case for simple arenes remains largely underdeveloped owing to the high aromatic stabilization energy. We herein report a dearomative sequential addition of two nucleophiles to arene π-bonds through umpolung of chromium-arene complexes. This mode enables divergent dearomative carbonylation reactions of benzene derivatives by tolerating various nucleophiles in combination with alcohols or amines under CO-gas-free conditions, thus providing modular access to functionalized esters or amides. The tunable synthesis of 1,3- or 1,4-cyclohexadienes as well as the construction of carbon quaternary centers further highlight the versatility of this dearomatization. Diverse late-stage modifications and derivatizations towards synthetically challenging and bioactive molecules reveal the synthetic utility. A possible mechanism was proposed based on control experiments and intermediate tracking.

Recent Progress in Synthesis of Alkyl Fluorinated Compounds with Multiple Contiguous Stereogenic Centers

Organic fluorides are widely used in pharmaceuticals, agrochemicals, material sciences, and other fields due to the special physical and chemical properties of fluorine atoms. The synthesis of alkyl fluorinated compounds bearing multiple contiguous stereogenic centers is the most challenging research area in synthetic chemistry and has received extensive attention from chemists. This review summarized the important research progress in the field over the past decade, including asymmetric electrophilic fluorination and the asymmetric elaboration of fluorinated substrates (such as allylic alkylation reactions, hydrofunctionalization reactions, Mannich addition reactions, Michael addition reactions, aldol addition reactions, and miscellaneous reactions), with an emphasis on synthetic methodologies, substrate scopes, and reaction mechanisms.

Catalytic asymmetric functionalization and dearomatization of thiophenes

The asymmetric synthesis of thiophene-derived compounds, including catalytic asymmetric dearomatization of thiophene and atroposelective synthesis of benzothiophene derivatives, has rarely been reported. In this work, the asymmetric transformation of the thiophene motif is investigated. Through the rational design of substrates with a thiophene structure, by using the vinylidene ortho-quinone methide (VQM) intermediate as a versatile tool, axially chiral naphthyl-benzothiophene derivatives and thiophene-dearomatized chiral spiranes were obtained in high yields with excellent enantioselectivities.

Phosphine vs DBU-Catalyzed Annulation Reactions of β'-Acetoxy Allenoates with Acyl-Tethered Benzothiazole Bisnucleophiles: (4 + 3) or (4 + 1) vs (3 + 3) Annulation

Dearomative annulation reaction of acyl-tethered benzothiazole bisnucleophiles with β'-acetoxy allenoates by switching the Lewis base is developed. The DBU-catalyzed reaction gives benzothiazole-fused 1,4-dihydropyridine carboxylates by (3 + 3) annulation chemoselectively. By contrast, the PR3-catalyzed reaction gives benzothiazole-fused azepines by (4 + 3) annulation and cyclopentene carboxylates by (4 + 1) annulation; the ratio of the latter two products depends on the solvent. A possible rationale for the difference in the reactivity, based on the 1,4/1,5-addition of the 2-acyl-tethered benzothiazole to the key phosphonium intermediate, is provided.

Copper-Catalyzed Dearomative trans-1,2-Carboamination

We have achieved the arenophile-mediated, copper-catalyzed dearomative trans-1,2-carboamination of nonactivated arenes with alkyl organometallic nucleophiles. This simple and practical procedure was used to prepare diverse, stereochemically rich alkylated cyclohexadienes from readily available arenes. Synthetic utility was demonstrated through the rapid preparation of complex small molecules difficult to access by conventional routes. Finally, we conducted DFT studies to explore the catalytic process, including a study of the reaction pathway and an examination of the divergent regioselectivity observed with substituted arenes.

Gd(III)-Catalyzed Regio-, Diastereo-, and Enantioselective [4 + 2] Photocycloaddition of Naphthalene Derivatives

Catalytic asymmetric dearomatization (CADA) reactions have evolved into an efficient strategy for accessing chiral polycyclic and spirocyclic scaffolds from readily available planar aromatics. Despite the significant developments, the CADA reaction of naphthalenes remains underdeveloped. Herein, we report a Gd(III)-catalyzed asymmetric dearomatization reaction of naphthalene with a chiral PyBox ligand via visible-light-enabled [4 + 2] cycloaddition. This reaction features application of a chiral Gd/PyBox complex, which regulates the reactivity and selectivity simultaneously, in excited-state catalysis. A wide range of functional groups is compatible with this protocol, giving the highly enantioenriched bridged polycycles in excellent yields (up to 96%) and selectivity (up to >20:1 chemoselectivity, >20:1 dr, >99% ee). The synthetic utility is demonstrated by a 2 mmol scale reaction, removal of directing group, and diversifications of products. Preliminary mechanistic experiments are performed to elucidate the reaction mechanism.

Asymmetric magnesium catalysis for important chiral scaffold synthesis

Magnesium catalysts are widely used in catalytic asymmetric reactions, and a series of catalytic strategies have been developed in recent years. Herein, in this review, we have tried to summarize asymmetric magnesium catalysis for the synthesis of important chiral scaffolds. Several important optically active motifs that are present in classic chiral ligands or natural products synthesized by Mg(II) catalytic methods are briefly discussed. Moreover, the representative mechanisms for different magnesium catalytic strategies, including in situ generated magnesium catalysts, are also shown in relation to synthetic routes for obtaining these important chiral scaffolds.

Photochemical dearomative skeletal modifications of heteroaromatics

Dearomatization has emerged as a powerful tool for rapid construction of 3D molecular architectures from simple, abundant, and planar (hetero)arenes. The field has evolved beyond simple dearomatization driven by new synthetic technology development. With the renaissance of photocatalysis and expansion of the activation mode, the last few years have witnessed impressive developments in innovative photochemical dearomatization methodologies, enabling skeletal modifications of dearomatized structures. They offer truly efficient and useful tools for facile construction of highly complex structures, which are viable for natural product synthesis and drug discovery. In this review, we aim to provide a mechanistically insightful overview on these innovations based on the degree of skeletal alteration, categorized into dearomative functionalization and skeletal editing, and to highlight their synthetic utilities.

Enantioselective Aminative Dearomatization of Indoles via Electrophilic 1,6-Addition of p-Quinone Diimides (p-QDIs)

Herein we report the first use of p-quinone diimide for the aminative dearomatization of 2,3-disubstituted indoles to furnish C3 aza-quaternary chiral indolenines. This approach, which proceeds via an electrophilic 1,6-addition of p-quinone diimide, allows the synthesis of an array of optically active aza-quaternary indolenines with high yields and excellent enantioselectivities. A one-pot approach of the same has also been established to further improve the synthetic accessibility of this protocol.

Dearomative [2 + 1] Spiroannulation of Bromophenols with Electron-Deficient Alkenes

A base-assisted dearomative [2 + 1] spiroannulation of p/o-bromophenols with activated olefins (methylenemalonates) to construct various cyclopropyl spirocyclohexadienone skeletons is reported. Furthermore, several other halophenols (X = Cl, I) were also tolerated in this process. Control experiments reveal a dearomative Michael addition of phenols at their halogenated positions to methylenemalonates, followed by intramolecular radical-based SRN1 dehalogenative cyclopropanation. However, according to the density functional theory (DFT) calculations, an SN2 dehalogenative cyclopropanation with the same low activation energy barrier should not be excluded. The utility of this method is showcased by gram-scale syntheses and transformations of the dearomatized products.

Pd-Catalyzed Asymmetric Intramolecular Dearomatizing Reductive Heck Reaction of Indoles

An enantioselective Pd-catalyzed intramolecular dearomative reductive Heck reaction of N-(o-bromoaryl) indole-3-carboxamide is developed. By employing Pd(dba)2/SPINOL-based phosphoramidite as the chiral catalyst and HCO2Na as the hydride source, a series of enantioenriched spiro indolines bearing vicinal stereocenters were afforded in moderate to good yields with excellent enantioselectivities. The reductive Heck reaction of formal tetrasubstituted alkene bearing β-hydrogens is therefore realized by inhibiting β-H elimination.

Rh(iii)-catalyzed sp3/sp2-C-H heteroarylations via cascade C-H activation and cyclization

The development of an efficient strategy for facile access to quinoline-based bis-heterocycles holds paramount importance in medicinal chemistry. Herein, we describe a unified approach for accessing 8-(indol-3-yl)methyl-quinolines by integrating Cp*Rh(iii)-catalyzed C(sp3)-H bond activation of 8-methylquinolines followed by nucleophilic cyclization with o-ethynylaniline derivatives. Remarkably, methoxybiaryl ynones under similar catalytic conditions delivered quinoline tethered spiro[5.5]enone scaffolds via a dearomative 6-endo-dig C-cyclization. Moreover, leveraging this method for C8(sp2)-H bond activation of quinoline-N-oxide furnished biologically relevant oxindolyl-quinolines. This reaction proceeds via C(sp2)-H bond activation, regioselective alkyne insertion, oxygen-atom-transfer (OAT) and intramolecular nucleophilic cyclization in a cascade manner. One C-C, one C-N and one C[double bond, length as m-dash]O bond were created with concomitant formation of a quaternary center.

Diastereoselective synthesis of functionalized spiroindolines via intramolecular ipso-iodocyclization/nucleophile addition cascade reactions of indole-tethered ynones

Herein, we describe a highly diastereoselective approach for synthesizing polyfunctionalized spiroindolines from indolyl-ynones involving an ipso-iodocyclization/nucleophile addition cascade. The developed strategy allows the formation of a spirocyclic core and the installation of two functional groups in a single operation. Also this strategy is accompanied by the generation of two C-C and one C-I bonds and two contiguous stereocenters.

Asymmetric Total Synthesis of (+)-Chuanxiongnolide L1 via a Stereoselective Oxidative Dearomatization/Diels-Alder Strategy

The first asymmetric total synthesis of chuanxiongnolide L1 was achieved in 16 steps and 1.9% overall yield by employing a bioinspired chiral auxiliary strategy. The key steps involving asymmetric oxidative dearomatization of chiral amino ether and subsequent asymmetric Diels-Alder reaction of the resulting masked chiral ortho-benzoquinone were adopted.