N-Heterocyclic Carbene Catalysis for Polycyclic Benzazepines Assembly: Regioselective Intramolecular Tandem Radical Cyclization.

A variety of polycyclic benzazepines were rapidly constructed by NHC-catalyzed regioselective redox-neutral intramolecular tandem cyclization. Initial mechanistic studies revealed that a SET radical process was possibly involved.

Defunctionalization Enabled by Intramolecular Radical Aromatic Substitution.

A chemoselective and regioselective copper-promoted defunctionalization procedure has been developed, enabling the rapid construction of various -polyheterocycles. Initial mechanistic studies reveal that a single-electron transfer radical process is potentially involved.

Photocatalyst-Free Visible Light-Induced C(sp)-H Arylation of Quinoxalin-2(1H)-ones and Coumarins.

Herein, we describe a visible light-induced C(sp)-H arylation method for quinoxalin-2(1H)-ones and coumarins using iodonium ylides without the need for external photocatalysts. The protocol demonstrates a broad substrate scope, enabling the arylation of diverse heterocycles through a simple and mild procedure. Furthermore, the photochemical reaction showcases its applicability in the efficient synthesis of biologically active molecules.

Visible-Light-Promoted C3-Sulfenylindoles with Arylsulfonyl Chlorides via Electron Donor-Acceptor Complex.

In this study, we present an efficient approach for the synthesis of 3-sulfenyl indoles through an electron donor-acceptor (EDA) complex-promoted photoreaction. This sulfenylation reaction leverages sulfonyl chlorides as the sulfur source and employs PPh as the reductant without the need for any transition-metal catalyst or photocatalyst. At the same time, the relaxation process of the excited EDA complex was theoretically investigated at the method and multiconfiguration second-order perturbation//complete active space self-consistent field/PCM level of theory, which involves the π bond of indoles injecting an electron to the antibonding orbital of the S-Cl bond in arylsulfonyl chlorides.

Heterogeneous Photocatalytic Ring Expansion of Cyclic Ketones for the Construction of Medium-Sized Lactams.

Construction of medium-sized ring compounds remains challenging in synthetic chemistry. Herein, we describe the synthesis of medium-sized lactams via a photoinduced ring expansion of benzo-fused cyclic ketones using graphitic carbon nitride (g-CN) as a photocatalyst. The ring expansion protocol provided an efficient access to 8-10-membered lactams in good yields and displayed good tolerance to a range of functional groups.

Rhodium-Catalyzed C(sp)-O Cross Couplings of Diazo Quinones with Phenols to Construct Diaryl Ethers.

The diaryl ether represents a prevalent structural motif found in numerous biologically active molecules. Herein, we describe a dirhodium-catalyzed C(sp)-O cross coupling reaction between diazo quinones and phenols for the construction of diaryl ethers in moderate to high yields. The reaction proceeds under mild and neutral conditions and is tolerant of various functional groups.

Heterogeneous Photocatalytic C-H Functionalization of Indoles with Diazo Compounds Enabled by Carbon Nitride.

Herein, we reported the heterogeneous photocatalytic C-H alkylation of indoles with diazo compounds using graphitic carbon nitride (g-CN) as the photocatalyst. The reaction was carried out under a simple operation and mild conditions. In addition, the catalyst was found to be stable and reusable after five reaction cycles.

Metal-Free Generation of γ-Cyanoalkyl Radicals by N-Heterocyclic Carbene Catalysis: Assembly of 6-Cyanoalkyl Phenanthridines.

A number of γ-cyanoalkyl radicals were generated by sustainable N-heterocyclic carbene catalysis in tin-, transition-meal-, and light-free conditions, followed by insertion into biaryl isonitriles, thus leading to the rapid assembly of a variety of diversely functionalized 6-cyanoalkyl phenanthridines. A preliminary mechanism study revealed that a single-electron transfer radical process was possibly involved.

Asymmetric dearomative cyclopropanation of naphthalenes to construct polycyclic compounds.

Catalytic asymmetric dearomatization (CADA) reactions is an important synthetic method for constructing enantioenriched complex cyclic systems from simple aromatic feedstocks. However, the CADA reactions of nonactivated arenes, such as naphthalenes and benzenes, have been far less explored than those of electronically activated arenes, such as phenols, naphthols and indoles. Herein, we disclose an asymmetric dearomative cyclopropanation of naphthalenes for the rapid construction of polycyclic compounds.

Divergent Construction of Heterocycles by SOMOphilic Isocyanide Insertion under N-Heterocyclic Carbene Catalysis.

A variety of phenanthridines are rapidly constructed by an N-heterocyclic carbene (NHC)-catalyzed SOMOphilic isocyanide insertion-initiated homolytic aromatic substitution-type radical cyclization in the absence of any light, transition metals, and external oxidants. The aldehyde-free, scalable, and operationally simple protocol tolerates diverse functionalized biaryl isonitriles and activated α-halides. Moreover, it can be further applied to the divergent construction of other N-heterocycles.

Construction of -Polyheterocycles by -Heterocyclic Carbene Catalysis via a Regioselective Intramolecular Radical Addition/Cyclization Cascade.

-Polyheterocycles are rapidly accessed by -heterocyclic carbene (NHC) catalysis through regioselective sequential radical addition/cyclization in the absence of any metals or oxidants. The transformation occurs under mild conditions and enjoys a wide substrate scope with excellent functional group compatibility. Furthermore, a gram-scale synthesis is also conducted.

Halogen-Bonding-Promoted C-H Malonylation of Indoles under Visible-Light Irradiation.

Herein, we report a halogen-bonding-based electron donor-acceptor (EDA) complex-promoted photoreaction for the synthesis of C2-malonylated indoles. The protocol provides access to a broad range of functionalized indoles in good yields through the coupling reaction of indoles with diethyl bromomalonate under visible-light irradiation without the need for any transition-metal catalyst or photocatalyst.

Visible-Light Carbon Nitride-Catalyzed Aerobic Cyclization of Thiobenzanilides under Ambient Air Conditions.

A metal-free heterogeneous photocatalysis has been developed for the synthesis of benzothiazoles via intramolecular C-H functionalization/C-S bond formation of thiobenzanilides by inexpensive graphitic carbon nitride (g-CN) under visible-light irradiation. This reaction provides access to a broad range of 2-substituted benzothiazoles in high yields under an air atmosphere at room temperature without addition of a strong base or organic oxidizing reagents. In addition, the catalyst was found to be stable and reusable after five reaction cycles.

Chemoselective Rearrangement Reactions of Sulfur Ylide Derived from Diazoquinones and Allyl/Propargyl Sulfides.

Here, we describe three types of rearrangement reactions of sulfur ylide derived from diazoquinones and allyl/propargyl sulfides. With Rh(esp) as the catalyst, diazoquinones react with allyl/propargyl sulfides to form a sulfur ylide, which undergoes a chemoselective tautomerization/[2,3]-sigmatropic rearrangement reaction, a Doyle-Kirmse rearrangement/Cope rearrangement cascade reaction, or a Doyle-Kirmse rearrangement/elimination reaction, depending on the substituent of the sulfides. The protocol provides alkenyl and allenyl sulfides and multisubstituted phenols with moderate and high yields.

Iron- and cobalt-catalyzed C(sp)-H bond functionalization reactions and their application in organic synthesis.

Direct C-H bond functionalization catalyzed by non-precious transition metals is an attractive strategy in synthetic chemistry. Compared with the precious metals rhodium, palladium, ruthenium, and iridium commonly used in this field, catalysis based on non-precious metals, especially the earth-abundant ones, is appealing due to the increasing demand for environmentally benign and sustainable chemical processes. Herein, developments in iron- and cobalt-catalyzed C(sp)-H bond functionalization reactions are described, with an emphasis on their applications in organic synthesis, i.

Transition-Metal-Free C(sp )-C(sp ) Cross-Coupling of Diazo Quinones with Catechol Boronic Esters.

A transition-metal-free C(sp )-C(sp ) bond formation reaction by the cross-coupling of diazo quinones with catechol boronic esters was developed. With this protocol, a variety of biaryls and alkenyl phenols were obtained in good to high yields under mild conditions. The reaction tolerates various functionalities and is applicable to the derivatization of pharmaceuticals and natural products.

Iron-Catalyzed Highly Enantioselective cis-Dihydroxylation of Trisubstituted Alkenes with Aqueous H O.

Reliable methods for enantioselective cis-dihydroxylation of trisubstituted alkenes are scarce. The iron(II) complex cis-α-[Fe (2-Me -BQPN)(OTf) ], which bears a tetradentate N ligand (Me -BQPN=(R,R)-N,N'-dimethyl-N,N'-bis(2-methylquinolin-8-yl)-1,2-diphenylethane-1,2-diamine), was prepared and characterized. With this complex as the catalyst, a broad range of trisubstituted electron-deficient alkenes were efficiently oxidized to chiral cis-diols in yields of up to 98 % and up to 99.

Iron porphyrin catalysed light driven C-H bond amination and alkene aziridination with organic azides.

Visible light driven nitrene transfer and insertion reactions of organic azides are an attractive strategy for the design of C-N bond formation reactions under mild reaction conditions, the challenge being lack of selectivity as a free nitrene reactive intermediate is usually involved. Herein is described an iron(iii) porphyrin catalysed sp C-H amination and alkene aziridination with selectivity by using organic azides as the nitrogen source under blue LED light (469 nm) irradiation. The photochemical reactions display chemo- and regio-selectivity and are effective for the late-stage functionalization of natural and bioactive compounds with complexity.

Stable group 8 metal porphyrin mono- and bis(dialkylcarbene) complexes: synthesis, characterization, and catalytic activity.

Alkyl-substituted carbene (CHR or CR, R = alkyl) complexes have been extensively studied for alkylcarbene (CHR) ligands coordinated with high-valent early transition metal ions (a.k.a.

Chiral -iron(ii) complexes with metal- and ligand-centered chirality for highly regio- and enantioselective alkylation of N-heteroaromatics.

Iron-catalyzed highly regio- and enantioselective organic transformations with generality and broad substrate scope have profound applications in modern synthetic chemistry; an example is herein described based on -Fe complexes having metal- and ligand-centered chirality. The -β Fe(N) complex [Fe(L)(OTf)] (L = ,'-bis(2,3-dihydro-1-cyclopenta-[]quinoline-5-yl)-,'-dimethylcyclohexane-1,2-diamine) is an effective chiral catalyst for highly regio- and enantioselective alkylation of N-heteroaromatics with α,β-unsaturated 2-acyl imidazoles, including asymmetric N1, C2, C3 alkylations of a broad range of indoles (34 examples) and alkylation of pyrroles and anilines (14 examples), all with high product yields (up to 98%), high enantioselectivity (up to >99% ee) and high regioselectivity. DFT calculations revealed that the "chiral-at-metal" -β configuration of the iron complex and a secondary π-π interaction are responsible for the high enantioselectivity.

Iridium(III)-Catalyzed Intermolecular C(sp )-H Insertion Reaction of Quinoid Carbene: A Radical Mechanism.

Described herein is an Ir /porphyrin-catalyzed intermolecular C(sp )-H insertion reaction of a quinoid carbene (QC). The reaction was designed by harnessing the hydrogen-atom transfer (HAT) reactivity of a metal-QC species with aliphatic substrates followed by a radical rebound process to afford C-H arylation products. This methodology is efficient for the arylation of activated hydrocarbons such as 1,4-cyclohexadienes (down to 40 min reaction time, up to 99 % yield, up to 1.

Ruthenium(II) Porphyrin Quinoid Carbene Complexes: Synthesis, Crystal Structure, and Reactivity toward Carbene Transfer and Hydrogen Atom Transfer Reactions.

Reactivity study of novel metal carbene complexes can offer new opportunities in catalytic carbene transfer reactions as well as in other synthetic protocols. Metal complexes with quinoid carbene (QC) ligands are assumed to be key intermediates in a variety of metal-catalyzed QC transfer reactions using diazo quinones, which demands development of the chemistry of QC transfer of well characterized metal-QC complexes. Herein we report the isolation and QC transfer of ruthenium porphyrins [Ru(Por)(QC)] which contribute the first examples of (i) structurally characterized metal-QC complex (by X-ray crystallography) and (ii) isolated metal-QC complex that undergoes QC transfer reaction.

An Effective [Fe(TFDMAP)Cl] Catalyst for C-H Bond Amination with Aryl and Alkyl Azides.

[Fe(TFDMAP)Cl] can efficiently catalyze intermolecular sp C-H amination using aryl azides and intramolecular sp C-H amination of alkyl azides in moderate-to-high product yields. At catalyst loading down to 1 mol %, the reactions display high chemo- and regioselectivity with broad substrate scope and are effective for late-stage functionalization of complex natural/bioactive molecules.

Perfluoroalkyl Aziridines with Ruthenium Porphyrin Carbene Intermediates.

A new and efficient synthesis of multifunctionalized perfluoroalkyl aziridines via a ruthenium-perfluoroalkylcarbene intermediate is described. With Ru( p-Cl-TPP)CO as the catalyst, in situ generated C FCHN from C FCHNHCl underwent a cascade of nitrone formation/1,3-diploar cycloaddition/rearrangement reactions with nitrosoarenes and alkynes to give a variety of multifunctionalized perfluoroalkyl aziridines in good to high yields and with moderate to high diastereoselectivity. The ruthenium-perfluoroalkylcarbene intermediates obtained through the stoichiometric reaction of ruthenium porphyrin and C FCHN were spectroscopically characterized.

Rh -Catalyzed Intermolecular C-H Arylation of Aromatics with Diazo Quinones.

We developed an efficient synthesis of biaryls by a dirhodium(II)-catalyzed aromatic C-H arylation with diazo quinones. The new biaryl synthesis can be performed under mild and neutral conditions and without directing group chelation assistance. The reaction tolerates various functionalities and is applicable to a broad range of aromatics.