Feng Ligand: Privileged Chiral Ligand in Asymmetric Catalysis

Sc-Catalyzed Asymmetric [2 + 2] Annulation of 2-Alkynylnaphthols with Dienes to Access Cyclobutene Frameworks

Herein, we introduce a scandium-catalyzed synthetic strategy that provides access to a diverse and functionalized array of cyclobutene frameworks adorned with a quaternary carbon center. This approach broadens the synthetic repertoire of 2-alkynylnaphthols with alkenes, offering a versatile platform for the construction of complex molecular architectures. The asymmetric catalytic [2 + 2] cycloaddition reaction demonstrates a wide substrate scope and an impressive functional group tolerance, yielding products with high efficiency, up to 97% yield, and excellent enantiomeric excess of up to 97%. The simplicity of scaling up this process, coupled with the ease of converting these cyclobutene frameworks into a variety of substituted products, significantly enhances the synthetic utility of this method.

Asymmetric Synthesis of Optically Active Pyrazolidines or Pyrazoline Derivatives via Ni(II)-Bipyridine-N,N'-dioxide Complexes

Easily obtainable and efficient chiral C2-symmetric bipyridine-N,N'-dioxide ligands with Ni(OTf)2 were developed for application in catalyzing [3 + 2] cycloaddition reactions to synthesize optically active fused pyrazolidines or pyrazoline derivatives featuring three contiguous stereogenic centers by employing azomethine imines and α,β-unsaturated 2-acyl imidazoles, affording the corresponding adducts with the opposite configuration compared to previous synthetic products in 80-98% yields with 28-99% ee and >20:1 dr. In addition, subsequent amplification experiments and derivative transformations of the product further demonstrated the efficient catalytic performance of the catalyst Ni(II)-bipyridine-N,N'-dioxide complexes and the practicality of this synthesis methodology.

Synthesis of γ-Butyrolactones with Chiral Quaternary-Tertiary Stereocenters via Catalytic Asymmetric Mukaiyama-Michael Addition

A catalytic asymmetric Mukaiyama-Michael reaction of silyl ketene acetals (SKAs) with α- or β-substituted α,β-unsaturated pyrazolamides was realized with N,N'-dioxide/nickel(II) complex catalysts. Bidentate coordination of the substrate to the catalyst and elongation of the ligand were beneficial for stereocontrol. In addition, adjustment of the substituents on substrates tuned the reactivity significantly. A wide range of chiral γ-butyrolactones with quaternary-tertiary stereocenters were obtained in moderate to excellent yields, good diastereomeric ratio, and excellent enantiomeric excess values.

Asymmetric catalytic concise synthesis of 3-(3-indolomethyl)-oxindoles for the construction of trigolute analogs

Asymmetric synthesis of 3-(3-indolomethyl)oxindoles through the addition of indole-substituted enolized ketoesters to 3-bromo-3-substituted oxindoles has been achieved using a N,N'-dioxide/Ho(III) complex. A number of 3-(3-indolomethyl)oxindoles, which may possess biological activity, were obtained in good yields with high diastereo- and enantioselectivities (up to 97% yield, >19 : 1 dr, 98% ee). Furthermore, time-dependent reversal of diastereoselectivity enabled access to optically active diastereomers. The product followed by facile transformations gave a new route into trigolute analogs.

Tandem catalytic allylic C-H amination and asymmetric [2,3]-rearrangement via bimetallic relay catalysis

A bimetallic relay catalysis protocol for tandem allylic C-H amination and asymmetric [2,3]-sigmatropic rearrangement has been developed with the use of an achiral Pd0 catalyst and a chiral N,N'-dioxide-MgII complex in a one-pot operation. A series of anti-α-amino derivatives containing two stereogenic centers were prepared from readily available allylbenzenes and glycine pyrazolamide with good yields and high stereoselectivities. Moreover, the synthetic potential of this protocol was further demonstrated by the product transformations, and a catalytic cycle was proposed to illustrate the reaction process.

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.

Concise synthesis of chiral γ-butenolides via an allylation/lactonization cascade reaction

A highly enantioselective allylation/lactonization cascade was developed, which provides a concise and efficient route to chiral γ-butenolides under mild conditions. Most of the reaction examples can be completed in 10 minutes with high selectivity.

Visible-Light-Promoted Enantioselective Acylation and Alkylation of Aldimines Enabled by 9-Fluorenone Electron-Shuttle Catalysis

Chiral acyclic α-tertiary amino ketones are widely present in various natural products and pharmaceuticals; however, the direct synthesis of this pharmacophore through a robust strategy still presents significant challenges. The emerging photocatalysis provides a powerful approach to construct chemical bonds that are difficult to form via a traditional two-electron pathway. Herein, we developed visible-light-induced chiral Lewis acid-catalyzed highly enantioselective acylation/alkylation of aldimines enabled by cooperative FLN (9-fluorenone) electron-shuttle catalysis via radical addition. An array of α-tertiary amino ketones, β-amino alcohols, and chiral amines were achieved with high yields and good to excellent stereocontrol (87 examples, up to 84% yield, 96% ee). These products can be easily transformed into valuable and bioactive skeletons. Extensive control experiments, detailed mechanism studies, and density functional theory calculations elucidated the reaction process and highlighted the crucial role played by FLN.

Asymmetric catalytic [1,3]- or [3,3]-sigmatropic rearrangement of 3-allyloxy-4H-chromenones and their analogues

A highly efficient asymmetric [1,3]- and [3,3]-O-to-C sigmatropic rearrangement of 3-allyloxy-4H-chromenones and their analogues was developed. Chiral N,N'-dioxide complexes of 3d late transition metal complexes enabled two mechanistically different processes, giving a series of optically active 2,2-disubstituted chromane-3,4-diones and 2-allyl-3-hydroxy-4H-chromen-4-ones as well as their related compounds in excellent yield and enantioselectivity. Systemic mechanistic studies and DFT calculation revealed the nature of the vinyl ether unit of the substrate, which biased regioselectivity via a stepwise tight ion pair pathway and a concerted pericyclic pathway, respectively. The enantioselectivity of the two processes is also disclosed.

Asymmetric dearomatization of benzyl 1-naphthyl ethers via [1,3] O-to-C rearrangement

A catalytic asymmetric dearomatization reaction of benzyl 1-naphthyl ethers accelerated by a chiral N,N'-dioxide/Co(II) complex is disclosed. The reaction proceeds via an enantioselective [1,3] O-to-C rearrangement through a tight ion-pair pathway, providing a wide array of α-naphthalenone derivatives bearing an all-carbon quaternary center in high yields with excellent ee values.

Iron-Catalyzed Asymmetric Imidation of Sulfides via Sterically Biased Nitrene Transfer

Transition-metal-catalyzed enantioselective nitrene transfer to sulfides has emerged as one of the most powerful strategies for rapid construction of enantioenriched sulfimides. However, achieving stereocontrol over highly active earth-abundant transition-metal nitrenoid intermediates remains a formidable challenge compared with precious metals. Herein, we disclose a chiral iron(II)/N,N'-dioxide-catalyzed enantioselective imidation of dialkyl and alkyl aryl sulfides using iminoiodinanes as nitrene precursors. A series of chiral sulfimides were obtained in moderate-to-good yields with high enantioselectivities (56 examples, up to 99% yield, 98:2 e.r.). The utility of this methodology was demonstrated by late-stage modification of complex molecules and synthesis of the chiral insecticide sulfoxaflor and the intermediates of related bioactive compounds. Based on experimental studies and theoretical calculations, a water-bonded high-spin iron nitrenoid species was identified as the key intermediate. The observed stereoselectivity was original from the steric repulsion between the amide unit of the ligand in the chiral cave and the bulky substituent of sulfides. Additionally, dioxazolones proved to be suitable acylnitrene precursors in the presence of an iron(III)/N,N'-dioxide complex, resulting in the formation of enantioselectivity-reversed sulfimides (14 examples, up to 81% yield, 97:3 e.r.).

Photoredox-catalyzed C(sp3)─H radical functionalization to enable asymmetric synthesis of α-chiral alkyl phosphine

α-Chiral alkyl phosphines are privileged structural motifs with a wide application in organic and medical synthesis. It is highly desirable to develop stereoselective methods to prepare these enantioenriched molecules. The incorporation of C(sp3)─H functionalization and chiral phosphine chemistry is much less explored, probably because of the weak reactivity of C(sp3)─H bonds and/or the challenging site- and stereoselectivity issues. Herein, we disclose a synergistic catalysis system to enable an enantioselective radical addition process of α-substituted vinylphosphine oxides. An array of diverse α-chiral alkyl phosphors compounds is smoothly accessed by using the readily available chemicals as the inert C(sp3)─H bond reagent, such as sulfides, amines, alkenes, and toluene derivatives, exerting remarkable chemo-, site-, and enantioselectivity. On the basis of the mechanistic studies, both the C(sp3)─H bond activation and the stereochemistry-determining step are proposed to involve a single-electron transfer/proton transfer process.

Bipyridine-N,N'-dioxides Catalysts: Design, Synthesis, and Application in Asymmetric Synthesis of 1H-Pyrazolo[3,4-b]pyridine Analogues

A novel type of highly efficient chiral C2-symmetric bipyridine-N,N'-dioxides ligand application in catalyzing Michael addition/Cyclization of 5-aminopyrazoles with α,β-unsaturated 2-acyl imidazoles has been developed, affording the corresponding adducts in 85-97% yield with up to 99% enantioselectivity under mild conditions with a lower catalyst loading and broad scope. Remarkably, this protocol exhibits advantages in terms of reactivity and enantioselectivity, giving the fact that as low as 2.2 mol % of L1 and 2.0 mol % of Ni(OTf)2 can promote the title reaction on gram scale to afford the desired product with excellent enantioselectivity.

Enantioselective sulfonylation to construct 3-sulfonylated oxindoles

Asymmetric synthesis of 3-sulfonylated 3-substituted oxindoles through the addition of sodium sulfinate salts to 3-bromo-3-substituted oxindoles has been achieved using chiral nickel complexes of N,N'-dioxides. This method facilitates the creation of diverse chiral sulfonyl oxindoles, several of which display promising anticancer properties. Notably, the catalyst demonstrates remarkable tolerance to water, crucial for maintaining enantioselectivity. Furthermore, the utilization of topographic steric maps of the catalysts offers valuable insights into the mechanism underlying enantioselection reversal.

Water-enabling strategies for asymmetric catalysis

Water possesses unique advantages, including abundance, environmental friendliness and mild effects. Undoubtedly, it is an ideal solvent or reagent in chemical syntheses. Water also shows unique abilities in catalytic asymmetric synthesis. It can accelerate reaction rates, improve diastereo- or enantioselectivities, initiate reactions, diversify chemo, diastereo- or enantioselectivities through various effects (hydrophobic, hydrogen bonding, protonation). Several reviews have demonstrated the positive effects of water in asymmetric synthesis. In this review, we summarize water-enabling strategies in the last decade, and focus on advances which reveal how water affects a reaction.

Iron-Catalyzed Asymmetric α-Alkylation of 2-Acylimidazoles via Dehydrogenative Radical Cross-Coupling with Alkanes

The direct α-alkylation of acyclic carbonyls with nonactivated hydrocarbons through C(sp3 )-H functionalization is both extremely promising and notably challenging, especially when attempting to achieve enantioselectivity using iron-based catalysts. We have identified a robust chiral iron complex for the oxidative cross-coupling of 2-acylimidazoles with benzylic and allylic hydrocarbons, as well as nonactivated alkanes. The readily available and tunable N,N'-dioxide catalysts of iron in connection with oxidants exhibit precise asymmetric induction (up to 99 % ee) with good compatibility in moderate to good yields (up to 88 % yield). This protocol provides an elegant and straightforward access to optically active acyclic carbonyl derivatives starting from simple alkanes without prefunctionalization. Density functional theory (DFT) calculations and control experiments were made to gain insight into the nature of C-C bond formation and the origin of enantioselectivity. We propose a radical-radical cross-coupling process enabled by the immediate interconversion between chiral ferric species and ferrous species.

Catalytic Asymmetric Synthesis of Axially and Centrally Chiral 1,2-Dihydrobenzofuro[3,2-b]pyridines through a [2 + 2] Cycloaddition/Retroelectrocyclization/Re-Cycloaddition Cascade

A catalytic asymmetric tandem cyclization of azadienes and ortho-alkynylnaphthols accelerated by the chiral N,N'-dioxide-gadolinium(III) complex is disclosed. This method allows the synthesis of a range of 1,2-dihydrobenzofuro[3,2-b]pyridines containing both axially and centrally chiral elements in high yields and excellent stereoselectivities (up to >99% yield, 91:9 dr, 98% ee). A control experiment revealed that this process proceeded through a multistep [2 + 2] cycloaddition/retroelectrocyclization/tautomerism/1,6-conjugate addition cascade.

Chiral N,N'-Dioxide Ligands Tune Diastereoselectivity in Mg(II)-Catalyzed Asymmetric Ring-Opening Desymmetrization of Azetidiniums

A diastereodivergent asymmetric desymmetrization of azetidinium salts with benzothiazoleamides as carbon nucleophiles through a chiral N,N'-dioxide/Mg(II) complex-promoted ring-opening reaction is realized by tuning ligands. Both syn- and anti-chiral δ-amino acid derivatives bearing benzothiazole structure were obtained in moderate to good yields and dr and ee values. DFT calculations indicated that the diastereodivergency stems from the different size of the chiral pocket formed by variable substructures of the ligands, leading to the opposite attack direction of the nucleophiles.

Chiral Lewis Acid-Catalyzed Asymmetric Multicomponent Michael Reaction through [1,2]-Phospha-Brook Rearrangement

The multicomponent catalytic asymmetric Pudovik addition/[1,2]-phospha-Brook rearrangement/Michael reaction sequence of isatins, phosphites, and 4-oxobutenoates was realized. A series of oxindole derivatives containing two contiguous stereocenters was obtained in high yields and excellent stereoselectivities (up to >99% yield, >95:5 dr, >99% ee) using a chiral Lewis acid catalyst. A possible catalytic model is presented to illustrate the stereocontrol.

Bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction for construction of 5-oxazoylmethyl α-silyl alcohol

A bimetallic tandem catalysis-enabled enantioselective cycloisomerization/carbonyl-ene reaction was developed. The reaction proceeded well with a broad range of N-propargylamides and acylsilanes, affording the target chiral 5-oxazoylmethyl α-silyl alcohols in up to 95% yield and 99% ee under mild conditions. Importantly, this facile protocol was available for the late-stage modification of several bioactive molecules. Based on the mechanistic study and control experiments, a possible catalytic cycle and transition state are proposed to elucidate the reaction process and enantioinduction.

Sterically Hindered and Deconjugative α-Regioselective Asymmetric Mannich Reaction of Meinwald Rearrangement-Intermediate

Compared to γ-addition, the α-addition of α-branched β,γ-unsaturated aldehydes faces larger steric hindrance and disrupts the π-π conjugation, which might be why very few examples are reported. In this article, a highly diastereo- and enantioselective α-regioselective Mannich reaction of isatin-derived ketimines with α-, β- or γ-branched β,γ-unsaturated aldehydes, generated in situ from Meinwald rearrangement of vinyl epoxides, is realized by using chiral N,N'-dioxide/Sc^III catalysts. A series of chiral α-quaternary allyl aldehydes and homoallylic alcohols with vicinal multisubstituted stereocenters are constructed in excellent yields, good d.r. and excellent ee values. Experimental studies and DFT (density functional theory) calculations reveal that the large steric hindrance of the ligand and the Boc (tButyloxy carbonyl) protecting group of imines are critical factors for the α-regioselectivity.

Enantioselective anti-Dihalogenation of Electron-Deficient Olefin: A Triplet Halo-Radical Pylon Intermediate

The textbook alkene halogenation reaction establishes straightforward access to vicinal dihaloalkanes. However, a robust catalytic method for dihalogenizing electron-deficient olefins in an enantioselective manner is still under development, and its mechanism remains controversial. Herein, we disclose efficient regio-, anti-diastereo-, and enantioselective dibromination, bromochlorination, and dichlorination reactions of enones catalyzed by a chiral N,N'-dioxide/Yb(OTf)₃ complex. With the combination of electrophilic halogen and halide salts as halogenating agents, an array of homo- and heterodihalogenated derivatives is achieved in moderate to good enantioselectivities. Moreover, DFT calculations reveal that a novel triplet halo-radical pylon intermediate is probable in accounting for the exclusive regio- and anti-diastereoselectivity.

Asymmetric synthesis of complex tricyclo[3.2.2.0]nonenes from racemic norcaradienes: kinetic resolution via Diels-Alder reaction

Herein, the enantioselective synthesis of complex tricyclo[3.2.2.0]nonenes through the Diels-Alder reaction is reported. Utilizing racemic norcaradienes prepared from the visible-light-mediated dearomative cyclopropanation of m-xylene as dienes and enone derivatives as dienophiles, the overall process represents a kinetic asymmetric transformation in the presence of a chiral cobalt(ii) complex of chiral N,N'-dioxide. High diastereo- and enantioselectivity could be obtained in most cycloaddition processes and part racemization of norcaradiene is observed. The topographic steric maps of the catalysts were collected to rationalize the relationship between reactivity and enantioselectivity with the catalysts.

Enantioselective [3+2] Cycloaddition of Donor-Acceptor Aziridines and Imines to Construct 2,5-trans-Imidazolidines

An enantioselective [3+2] cycloaddition of donor-acceptor aziridines with N-aryl protected imines was developed with a Ni(ClO₄ )₂  ⋅ 6H₂ O/N,N'-dioxide catalyst system, providing a broad range of chiral trans-substituted imidazolidine compounds with good yields and excellent enantioselectivities (up to 99 % yield, up to 98 % ee). Control experiments indicated that the products could offer excellent diastereoselectivities with the control of chiral Ni(II)-N,N'-dioxide complex and the interaction of the substrates. The possible catalytic process was proposed to rationalize the stereocontrol.

Catalytic Enantioselective 6π Photocyclization of Acrylanilides

Controlling absolute stereochemistry in catalytic photochemical reactions is generally challenging owing to high rates of background reactivity. Successful strategies broadly rely on selective excitation of the reaction substrate when associated with a chiral catalyst. Recent studies have demonstrated that chiral Lewis acid complexes can enable selective energy transfer from a photosensitizer to facilitate enantioselective triplet state reactions. Here, we apply this approach to the enantioselective catalysis of a 6π photocyclization through the design of an iridium photosensitizer optimized to undergo energy transfer to a reaction substrate only in the presence of a chiral Lewis acid complex. Among a group of iridium(III) sensitizers, enantioselectivity and yield closely correlate with photocatalyst triplet energy within a narrow window enabled by a modest reduction in substrate triplet energy upon binding a scandium/ligand complex. These results demonstrate that photocatalyst tuning offers a means to suppress background reactivity and improve enantioselectivity in photochemical reactions.

[3,3]-Sigmatropic Rearrangements of Naphthyl 1-Propargyl Ethers: para-Propargylation and Catalytic Asymmetric Dearomatization

The para-Claisen rearrangement of aryl 1-propargyl ethers involves two-step [3,3]-sigmatropic rearrangements and dearomatization process, which has high activation barriers and is of challenge. Here we discovered thermal para-Claisen rearrangement of naphthyl 1-propargyl ethers, and it enabled the formation of formal para-C-H propargylation products upon rearomatization. Chirality transfer occurred if optically active propargyl ethers were employed, leading to the construction of aryl/propargyl-containing stereogenic centers. Moreover, catalytic asymmetric dearomatization of naphthyl 1-propargyl ethers with different substitution at para-position gave access to benzocyclohexenones bearing all-carbon quaternary stereocenters. The reaction was accelerated by a chiral N,N'-dioxide/Co(OTf)₂ complex catalyst to achieve high yields (up to 98 %) and high enantioselectivities (up to 93 % ee). The DFT calculations and experimental results provided important clues to clarify the para-Claisen rearrangement process as well as the chiral induction and remote delivery.

Enantioselective Radical Addition to Ketones through Lewis Acid-Enabled Photoredox Catalysis

Photocatalysis opens up a new window for carbonyl chemistry. Despite a multitude of photochemical reactions of carbonyl compounds, visible light-induced catalytic asymmetric transformations remain elusive and pose a formidable challenge. Accordingly, the development of simple, efficient, and economic catalytic systems is the ideal pursuit for chemists. Herein, we report an enantioselective radical photoaddition to ketones through a Lewis acid-enabled photoredox catalysis wherein the in situ formed chiral N,N'-dioxide/Sc(III)-ketone complex serves as a temporary photocatalyst to trigger single-electron transfer oxidation of silanes for the generation of nucleophilic radical species, including primary, secondary, and tertiary alkyl radicals, giving various enantioenriched aza-heterocycle-based tertiary alcohols in good to excellent yields and enantioselectivities. The results of electron paramagnetic resonance (EPR) and high-resolution mass spectrum (HRMS) measurements provided favorable evidence for the stereocontrolled radical addition process involved in this reaction.

NickelII-catalyzed asymmetric photoenolization/Mannich reaction of (2-alkylphenyl) ketones

A diastereo- and enantioselective photoenolization/Mannich (PEM) reaction of ortho-alkyl aromatic ketones with benzosulfonimides was established by utilizing a chiral N,N'-dioxide/Ni(OTf)2 complex as the Lewis acid catalyst. It afforded a series of benzosulfonamides and the corresponding ring-closure products, and a reversal of diastereoselectivity was observed through epimerization of the benzosulfonamide products under continuous irradiation. On the basis of the control experiments, the role of the additive LiNTf2 in achieving high stereoselectivity was elucidated. This PEM reaction was proposed to undergo a direct nucleophilic addition mechanism rather than a hetero-Diels-Alder/ring-opening sequence. A possible transition state model with a photoenolization process was proposed to explain the origin of the high level of stereoinduction.

Enantioselective construction of cis-hydroindole scaffolds via an asymmetric inverse-electron-demand Diels-Alder reaction: application to the formal total synthesis of (+)-minovincine

cis-Hydroindole scaffolds widely exist in a large number of natural products, pharmaceuticals, and organocatalysts. Therefore, the development of efficient and enantioselective methods for the construction of cis-hydroindoles is of great interest and importance. Herein, a novel approach for the enantioselective synthesis of cis-hydroindole scaffolds has been realized through a chiral N,N'-dioxide/Mg(OTf)2 complex catalyzed asymmetric inverse-electron-demand Diels-Alder (IEDDA) reaction of 2-pyrones and cyclic enamines. A series of substituted cis-hydroindole derivatives bearing multiple contiguous stereocenters and functional groups were obtained in good to excellent yields and enantioselectivities (up to 99% yield, and 95% ee) under mild reaction conditions. Moreover, the enantioselective formal total synthesis of (+)-minovincine was concisely furnished with high efficiency and stereoselectivity to demonstrate the synthetic potential of this method.

Catalytic asymmetric amination of azlactones with azobenzenes

We reported an efficient asymmetric amination of azlactones with N-aryl-N-aroyldiazenes through a chiral N,N'-dioxide-based Lewis acid catalyst. The multicoordination ability of Nd(III) enabled it to simultaneously activate and to locate the two reactants for N-selective addition. Hydrazine-bearing azlactone derivatives were obtained in moderate to good yields with high enantioselectivity.

Photoinduced Chemo-, Site- and Stereoselective α-C(sp3 )-H Functionalization of Sulfides

The ubiquity of sulfur-containing molecules in biologically active natural products and pharmaceuticals has long attracted synthetic chemists to develop efficient strategies towards their synthesis. The strategy of direct α-C(sp³ )-H modification of sulfides provides a streamlining access to complex sulfur-containing molecules. Herein, we report a photoinduced chemo-, site- and stereoselective α-C(sp³ )-H functionalization of sulfides using isatins as the photoredox reagent and coupling partner catalyzed by a chiral gallium(III)-N,N'-dioxide complex. The reaction proceeds through a verified single-electron transfer (SET) mechanism with high efficiency, excellent functional group tolerance, as well as a broad substrate scope. Importantly, this cross-coupling protocol is highly selective for the direct late-stage functionalization of methionine-related peptides, regardless of the inherent structural similarity and complexity of diverse residues.

Bimetallic Palladium/Cobalt Catalysis for Enantioselective Allylic C-H Alkylation via a Transient Chiral Nucleophile Strategy

An asymmetric allylic C-H functionalization has been developed by making use of transient chiral nucleophiles, as well as bimetallic synergistic catalysis with an achiral Pd⁰ catalyst and a chiral N,N'-dioxide-Co^II complex. A variety of β-ketoesters and N-Boc oxindoles coupled with allylbenzenes and aliphatic terminal alkenes were well tolerated, furnishing the desired allylic alkylation products in high yields (up to 99 %) with excellent regioselectivities and enantioselectivities (up to 99 % ee).

Enantioselective Synthesis of Azetidines through [3 + 1]-Cycloaddition of Donor-Acceptor Aziridines with Isocyanides

The enantioselective [3 + 1]-cycloaddition of racemic donor-acceptor (D-A) aziridines with isocyanides was first realized under mild reaction conditions using a chiral N,N'-dioxide/Mg^II complex as catalyst, providing a facile route to enantioenriched exo-imido azetidines with good to excellent yield (up to 99%) and enantioselectivity (up to 94% ee). An obvious chiral amplification effect was observed in this system, and an explanation was elucidated based on the experimental investigation and X-ray crystal structure of the enantiomerically pure catalyst.

Synthesis of chiral pyridine-oxazolines via catalytic asymmetric Heine reaction of meso-N-(2-picolinoyl)-aziridines

An asymmetric Heine reaction of (meso)-N-(2-picolinoyl)-aziridines catalyzed by a chiral ytterbium(III)–N,N’-dioxide complex was established. A novel library of pyridine-oxazolines was obtained in decent yields and enantioselectivities, which show potential as...

Asymmetric catalytic nitrooxylation and azidation of β-keto amides/esters with hypervalent iodine reagents

Chiral Lewis acid-catalyzed enantioselective nitrooxylation and azidation of cyclic and acyclic β-keto amides/esters with hypervalent iodine(iii) reagents.

Enantioselective formal [2 + 2 + 2] cycloaddition of 1,3,5-triazinanes to construct tetrahydropyrimidin-4-one derivatives

A chiral Lewis acid-catalyzed enantioselective formal [2 + 2 + 2] cycloaddition of 1,3,5-triazinanes with azlactones or β,γ-unsaturated pyrazole amides was developed to synthesize chiral tertiary/quaternary tetrahydropyrimidin-4-one derivatives with good yields and enantioselectivities. Two competitive reaction pathways were proposed based on experiments.

Catalytic Asymmetric Halogenation/Semipinacol Rearrangement of 3-Hydroxyl-3-vinyl Oxindoles: A Stereodivergent Kinetic Resolution Process

A highly enantioselective halogenation/semipinacol rearrangement of isatin-derived allylic alcohols has been developed with a chiral N,N'-dioxide/Sc^III complex as catalyst. This strategy involved a pivotal stereodivergent kinetic resolution process and provided a facile and efficient entry to optically active halo-substituted quinolone derivatives and quinoline alkaloids with a quaternary stereocenter simultaneously under mild reaction conditions. Based on the control experiments together with kinetic studies and DFT calculations, a possible catalytic cycle was proposed to illustrate the reaction process and enantiocontrol.