Pd-Catalyzed Enantioselective Desymmetrizing 1,7-Enyne Cycloisomerization of Alkyne-Tethered Cyclopentenes

An enantioselective Pd-catalyzed intramolecular desymmetrizing cycloisomerization of N-(cyclopent-3-en-1-yl)propiolamides has been developed by employing a new chiral phosphoramidite ligand. A series of structurally unique bridged azabicycles are achieved in moderate to excellent yields with good E/Z selectivity and high enantioselectivity. Synthetic transformations are conducted to demonstrate the practical utility of this reaction.

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.

Copper-catalyzed intramolecular dearomative aza-Wacker reaction of indole

Herein, we describe a copper-catalyzed intramolecular dearomative amination of indoles via a formal aza-Wacker reaction. This protocol provides an efficient method to access aza-polycyclic indoline molecules bearing exocyclic CC bonds in moderate to excellent yields in the presence of molecular oxygen as an oxidant. It is worth noting that indolin-3-ones are achieved when employing C3-non-substituted indoles as substrates.

Pd-Catalyzed Intramolecular Dearomative [4 + 2] Cycloaddition of Naphthalenes with Arylalkynes

A Pd-catalyzed intramolecular dearomative [4 + 2] cycloaddition reaction of naphthalenes with arylalkynes is developed. The protocol provides a straightforward method to access a range of polycyclic dihydronaphthalenes containing two vicinal all-carbon stereocenters in moderate yields under mild conditions in an air atmosphere. The deuterium labeling experiment suggests a pathway involving electrophilic dearomatization followed by Friedel-Crafts cyclization. Several synthetic transformations of the product were conducted to demonstrate the utility of this reaction.

Nickel-Catalyzed Enantioselective Dearomative Heck-Reductive Allylic Defluorination Reaction of Indoles

Herein, we describe a nickel-catalyzed asymmetric dearomative aryl-difluoroallylation reaction of indoles with α-trifluoromethyl alkenes as an electrophilic coupling partner. The reaction proceeds via a cascade sequence involving dearomative Heck cyclization and reductive allylic defluorination. A series of gem-difluoroallyl substituted indolines are obtained in moderate to good yields (36-77% yield) with excellent enantioselectivity (up to 99% ee). The reaction features broad functional group tolerance, scaled-up synthesis, and late-stage diversification.

Cobalt-catalyzed enantioselective desymmetrizing reductive cyclization of alkynyl cyclodiketones

A highly enantioselective cobalt-catalyzed desymmetrizing reductive cyclization of alkynyl cyclodiketones has been developed. Under mild reaction conditions by employing HBpin as a reducing agent and ferrocene-based PHOX as a chiral ligand, a series of polycyclic tertiary allylic alcohols bearing contiguous quaternary stereocenters are achieved in moderate to excellent yields with excellent enantioselectivities (up to 99%). Broad substrate scope and high functional group compatibility are observed in this reaction. A CoH-catalyzed pathway involving alkyne hydrocobaltation followed by nucleophilic addition to the C[double bond, length as m-dash]O bond is proposed. Synthetic transformations of the product are conducted to demonstrate the practical utilities of this reaction.

A Photoenzymatic Strategy for Radical-Mediated Stereoselective Hydroalkylation with Diazo Compounds

Carbene insertion reactions initiated with diazo compounds have been widely used to develop unnatural enzymatic reactions. However, alternative functionalization of diazo compounds in enzymatic processes has been unexploited. Herein, we describe a photoenzymatic strategy for radical-mediated stereoselective hydroalkylation with diazo compounds. This method generates carbon-centered radicals through an ene reductase catalyzed photoinduced electron transfer process from diazo compounds, enabling the synthesis of γ-stereogenic carbonyl compounds in good yields and stereoselectivities. This study further expands the possible reaction patterns in photo-biocatalysis and offers a new approach to solving the selectivity challenges of radical-mediated reactions.

Dearomatizing [2+2+1] Spiroannulation of Indoles with Alkynes

A palladium-catalyzed dearomatizing [2+2+1] spiroannulation of indoles with two molecular internal alkynes is developed in the presence of Cu(OAc)₂/O₂ as the oxidant, in which a domino sequence including C-H activation of indole followed by consecutive Heck reactions is involved. A range of 3,3'-spiroindolines bearing tetrasubstituted cyclopentadiene moieties and exocyclic C═C bonds at C2 are obtained in moderate to excellent yields.

Enantioselective Pd-catalyzed dearomative reductive Heck and domino Heck-Suzuki reactions of 2-CF3-indoles

Highly enantioselective palladium-catalyzed dearomative reductive Heck reaction and domino Heck-Suzuki reaction of 2-CF₃-indoles have been developed. Using Pd(OAc)₂/(R)-Synphos as the catalyst and Et₃SiH as a hydride source, a variety of indolines bearing a 2-trifluoromethyl quaternary stereocenter were obtained via a dearomative reductive Heck reaction. Alternatively, using Pd(dba)₂/phosphoramidite as the catalyst and Ar₄BNa as a coupling partner, structurally diverse indolines containing two vicinal carbon stereocenters were afforded through the domino dearomative Heck-Suzuki reaction.

Aromatic π-Components for Enantioselective Heck Reactions and Heck/Anion-Capture Domino Sequences

Olefin functionalization represents one of the most important synthetic transformations in organic synthesis. Over the past decades, palladium-catalyzed enantioselective Heck reactions, and Heck/anion-capture domino sequences through olefin carbopalladation followed by termination of the resulting alkyl-Pd species have been extensively developed. Extension of the coupling partners from classical olefins to other π-components would enable further advances and open new space in this field. Aromatics are important and easily available bulk chemicals. Dearomative transformation of endocyclic aromatic π-bonds via the Heck reaction pathway provides an efficient and straightforward route to structurally diverse alicyclic compounds. Nevertheless, major challenges for this transformation include aromaticity breaking and reactivity and selectivity issues.Recently, we have engaged in developing catalytic enantioselective dearomative Heck reactions and related domino reactions. A range of heteroarenes and naphthalenes have been employed as novel π-coupling partners in these reactions. Through dearomative migratory insertion of endocyclic aromatic C-C π-bonds followed by interception of the transient alkyl-Pd species, enantioselective Heck reactions, reductive Heck reactions, Heck/anion-capture difunctionalization reactions, and heteroarenyne cycloisomerization reactions have been established. Relying on β-H elimination of the alkyl-Pd intermediate, we realized enantioselective dearomative Heck reactions with a range of aromatic partners, including heterocyclic indoles, pyrroles, furans, benzofurans, and more challenging carbocyclic naphthalenes. In order to avoid the utilization of organohalide electrophiles, heteroarenyne cycloisomerization reaction was developed by merging intermolecular alkyne hydropalladation with intramolecular dearomative Heck reaction. Cycloisomerization of alkyne-tethered indoles delivered chiral indolines in excellent enantioselectivities with 100% atom economy. On the other hand, Heck/anion-capture domino sequences were established through nucleophilic trapping of the alkyl-Pd intermediate. When HCO₂Na was employed as a capturing reagent, the enantioselective dearomative reductive Heck reaction of indoles was realized. By employing other nucleophiles, including alkynes, N-sulfonylhydrazones, and organoboron reagents, we developed a series of dearomative difunctionalization reactions. Two vicinal stereocenters with excellent enantio- and diastereoselectivities were constructed in the corresponding Heck/Sonogashira, Heck/vinylation, and Heck/borylation reactions. Moreover, dearomative 1,4-diarylation of naphthalenes was developed through Heck/Suzuki domino reactions, in which competitive C-H arylation and the direct Suzuki reaction were almost fully inhibited in the presence of a spiro-phosphoramidite ligand.In this Account, we provide a panoramic view of our results since 2015 on enantioselective Heck reactions and related domino sequences by extending the coupling partners from classical olefins to aromatic systems. Investigations outlined in this Account established straightforward and efficient access to a variety of structurally diverse chiral heteropolycyclic molecules starting from simple and planar aromatic compounds.

Enantioselective Dearomative [3 + 2] Umpolung Annulation of N-Heteroarenes with Alkynes

Enantioselective [3 + 2] annulation of N-heteroarenes with alkynes has been developed via a cobalt-catalyzed dearomative umpolung strategy in the presence of chiral ligand and reducing reagent. A variety of electron-deficient N-heteroarenes, including quinolines, isoquinolines, quinoxaline, and pyridines, and internal or terminal alkynes are employed in this reaction, showing a broad substrate scope and good functionality tolerance. Annulation of electron-rich indoles with alkynes is also developed. This protocol provides a straightforward access to a variety of N-spiroheterocyclic molecules in excellent enantioselectivities (76 examples, up to 99% ee).

NiH-catalyzed dearomative hydroalkylation of indoles

A NiH-catalyzed intermolecular dearomative hydroalkylation of indoles has been developed, which assembles an array of structurally diverse C2-alkylated indolines with moderate to excellent yields. This protocol exhibits good functional group...

[Expression of hepatocyte nuclear factor 4γ in gastric carcinoma and its role in cell proliferation and stemness]

Objective: To explore the role and molecular mechanism of hepatocyte nuclear factor 4γ (HNF4γ) in proliferation and stemness of gastric cancer. Methods: A total of 102 cases of paraffin-embedded gastric cancer tissues and matched adjacent gastric tissues and 42 cases of fresh-frozen tissues derived from gastric patients who received radical gastrectomy were collected from the First Affiliated Hospital of Zhengzhou University between 2012 to 2015. The expression of HNF4γ was tested by immunohistochemical staining, quantitative real-time polymerase chain reaction (qRT-PCR). HNF4γ overexpressed (AGS-HNF4γ) and shRNA silenced (HGC27-shHNF4γ) gastric cell lines were established. The effects of HNF4γ on cell proliferation and stemness were verified by XTT, clone formation and sphere formation assay. The expression of CD44 was detected by western blot. Results: The mRNA expression level of HNF4γ in fresh-frozen gastric cancer tissue was (12.43±2.702), which was significantly higher than (3.639±1.109) in normal tissue (P<0.001). The high protein expression rate of HNF4γ in paraffin-embedded gastric cancer tissues was 41.2% (42/102), which was significantly higher than 8.8% (9/102) in normal gastric mucosa tissue (P< 0.001). The protein expression of HNF4γ was closely related to the tumor differentiation, infiltration depth, lymph node metastasis and tumor stage (P<0.05). The median survival interval of patients with HNF4γ high expression was 25 months, the 3-year survival rate was 4.8% (2/42), significantly lower than 38 months and 51.7% (31/60) of patients with normal HNF4γ expression (P<0.001). The proliferation and CD44 protein expression of AGS-HNF4γ cells were significantly higher than those of the AGS-Vector cells. The number of clone formation, sphere formation rate of AGS-HNF4γ cells were 243.5±24.5 and (83.5±3.9)%, significantly higher than 81.0±16.0 and (21.8±5.6)% of AGS-Vector cells (P=0.030 and P=0.010, respectively). The proliferation and CD44 protein expression of HGC27-shHNF4 cells were significantly lower than those of the HGC27-vector cells. The number of clone formation, sphere formation rate of HGC27-shHNF4 cells were 26.0±1.0 and (20.8±8.4)%, significantly higher than 83.5±4.5 and (72.5±4.8)% of HGC27-vector cells (P=0.006 and P=0.030, respectively). Conclusions: HNF4γ is upregulated in the gastric cancer tissues and related with the poor prognosis of patients with gastric cancer. Overexpression of HNF4γ promotes the proliferation and remains the stemness of gastric cancer cells by upregulating the expression of CD44.

A Pd-catalyzed domino Larock annulation/dearomative Heck reaction

A highly efficient synthesis of indolines from N-bromobenzoyl o-iodoanilines and alkynes is developed via a domino Larock annulation/dearomative Heck reaction.

Synthesis of tetracyclic indolin-3-ones through Pd-catalyzed intramolecular deacetylative dearomatization of 3-acetoxy-indoles

An efficient palladium-catalyzed intramolecular deacetylative dearomatization reaction of 3-acetoxyindoles has been developed. A range of tetracyclic indolin-3-ones bearing C2-quaternary stereocenters are achieved in good yields, showing a wide substrate scope for this reaction. A preliminary enantioselective reaction is established to furnish the product in 63% ee by using (R,R,R)-phosphoramide-PE as a chiral ligand.

An efficient palladium-catalyzed intramolecular deacetylative dearomatization reaction of 3-acetoxyindoles is disclosed, affording tetracyclic indolin-3-ones bearing C2-quaternary stereocenters in good yields.

Pd-catalyzed dearomative arylborylation of indoles

A palladium-catalyzed dearomative arylborylation of indoles is reported, which provides straightforward access to structurally diverse indolines bearing vicinal tetrasubstituted and borylated trisubstituted stereocenters in moderate to good yields with excellent diastereoselectivities.

Palladium-catalyzed dearomative arylphosphorylation of indoles

A palladium-catalyzed dearomative arylphosphorylation reaction of indoles involving C–C/C–P bond formation is developed.

Enantioselective Friedel–Crafts C2-alkylation of 3-substituted indoles with trifluoropyruvates and cyclic N-sulfonyl α-ketiminoesters

Enantioselective Friedel–Crafts C2-alkylations of 3-substituted indoles with trifluoropyruvates and cyclic α-ketiminoesters were developed, delivering indole-containing α-hydroxyesters and α-aminoesters in excellent enantioselectivities.

Palladium-catalyzed asymmetric dearomative alkenylation of indoles through a reductive-Heck reaction

A highly enantioselective intramolecular dearomatizing olefination of indoles has been developed through a Pd-catalyzed reductive Heck reaction.

Construction of Benzylic Stereogenic Carbon Centers through Enantioselective Arylation Reactions

Compounds bearing chiral benzylic stereocenters are important and frequently occur in natural products and drug molecules. In this account, we discuss our recent results on the construction of ­benzylic stereogenic centers based on enantioselective arylation and related domino sequences, mainly including asymmetric Friedel–Crafts alkylation reactions and asymmetric Heck reactions.

1 Introduction

2 The Catalytic Asymmetric Friedel–Crafts Alkylation Reaction

2.1 Reactions of Electron-Deficient Alkenes

2.2 Reactions of Active Ketimines

2.3 Reactions of Nitrones

2.4 Reactions of Aziridines

3 The Asymmetric Heck Reaction

3.1 Dearomative Heck Reactions and Related Domino Sequences

3.2 Heck Reactions of in situ Formed Enamines

4 Conclusion and Outlook

Enantioselective [2 + 2] cycloaddition of N-allenamides with cyclic N-sulfonylketimines: access to polysubstituted azetidines bearing quaternary stereocenters

A Ni(ClO₄)₂-catalyzed enantioselective [2 + 2] cycloaddition of N-allenamides with cyclic N-sulfonylketimines was developed, which regioselectively occurred at the proximal C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds of the N-allenamides.

A Ni(ClO₄)₂-catalyzed enantioselective [2 + 2] cycloaddition of N-allenamides with cyclic N-sulfonylketimines was developed, which regioselectively occurred at the proximal CC bonds of the N-allenamides. Broad substrate scope of N-allenamides and cyclic N-sulfonylketimines was observed. A range of fused polysubstituted azetidines bearing quaternary stereocenters were afforded in good yields and with excellent enantioselectivities (up to 99%).

Enantioselective alkynylation of N-sulfonyl α-ketiminoesters via a Friedel–Crafts alkylation strategy

Enantioselective Ni(ClO₄)₂-catalyzed alkynylation of N-sulfonyl-α-ketiminoesters is developed via a Friedel–Crafts-type pathway, yielding propargylic amides bearing quaternary stereocenters in excellent enantioselectivities.

Spirooxindole synthesis via palladium-catalyzed dearomative reductive-Heck reaction

Synthesis of 3,2′-spiropyrrolidine oxindole scaffolds via palladium-catalyzed intramolecular dearomative reductive-Heck reaction and [2,3-b]quinolinones through direct C3-arylation.

Recent progress in transition-metal-catalyzed enantioselective indole functionalizations

Recent progress on the transition-metal-catalyzed enantioselective functionalization reaction of indoles is reviewed, which is mainly focused on asymmetric indole alkylations, arylations, cycloaddition reactions, and other reactions.

Cu(I)-Catalyzed Enantioselective Friedel-Crafts Alkylation of Indoles with 2-Aryl-N-sulfonylaziridines as Alkylating Agents

A highly enantioselective Friedel-Crafts alkylation of indoles with N-sulfonylaziridines as alkylating agents has been developed by utilizing the complex of Cu(CH3CN)4BF4/(S)-Segphos as a catalyst. A range of optically active tryptamine derivatives are obtained in good to excellent yields and enantioselectivities (up to >99% ee) via a kinetic resolution process.

Lewis Acid Catalyzed Friedel-Crafts Alkylation of Alkenes with Trifluoropyruvates

A Friedel-Crafts alkylation reaction of styrenes with trifluoropyruvates has been developed, which delivered allylic alcohols in excellent yields (up to 98%) using the Ni(ClO4)2·6H2O/bipyridine complex as a catalyst. The asymmetric reaction was catalyzed by the chiral Cu(OTf)2/bisoxazoline complex to afford the corresponding chiral allylic alcohols bearing trifluoromethylated quaternary stereogenic centers in moderate enantioselectivities (up to 75% ee).

Enantioselective Friedel-Crafts Alkylation Reactions of 3-Substituted Indoles with Electron-Deficient Alkenes

Highly enantioselective Friedel-Crafts C2-alkylation reactions of 3-substituted indoles with α,β-unsaturated esters and nitroalkenes were developed using chiral Lewis acids as catalysts, which afforded chiral indole derivatives bearing C2-benzylic stereogenic centers in good to excellent yields (up to 99%) and enantioselectivities (up to 96% ee).

Palladium-catalyzed dearomative arylalkynylation of indoles

A palladium-catalyzed indole dearomative bisfunctionalization via a domino arylation/alkynylation sequence to achieve tetracyclic indolines bearing vicinal tertiary and quaternary stereocenters.

Au-catalyzed ring-opening reactions of 2-(1-alkynyl-cyclopropyl)pyridines with nucleophiles

A novel method for the C-C bond cleavage of cyclopropanes was developed by gold-catalyzed cycloisomerization of 2-(1-alkynyl-cyclopropyl)pyridine with nucleophiles, which provides efficient access to structurally diverse indolizines under mild conditions. A series of N-, C- and O-based nucleophiles were involved in this reaction to afford the corresponding indolizines in modest to excellent yields.

Enantioselective Friedel–Crafts reaction of 4,7-dihydroindoles with β-CF3-β-disubstituted nitroalkenes

Indoles bearing C2-trifluoromethylated quaternary stereocenters were obtained with high enantioselectivities by Ni-catalyzed asymmetric Friedel–Crafts alkylation of 4,7-dihydroindoles and subsequent oxidation.