MeOTf- and TBD-Mediated Carbonylation of ortho-Arylanilines with CO2 Leading to Phenanthridinones

Macrocyclization of carbon dioxide with 3-triflyloxybenzynes and tetrahydrofuran: straightforward access to 14-membered macrolactones

A novel [2+2+5+5] macrocyclization of carbon dioxide with 3-triflyloxybenzynes and tetrahydrofuran has been disclosed for the first time under transition metal-free conditions. The reaction provides a facile method for the synthesis of a rare type of 14-membered macrocyclic lactone, which is potentially useful but difficult to access by existing methods.

Nickel-Catalyzed Lactamization Reaction of 2-Arylanilines with CO2

Transition-metal-catalyzed lactamization and lactonization of C-H bonds with CO2 assisted by the chelation of amino or hydroxyl groups have been developed but limited to the use of precious metal catalysts such as palladium and rhodium. In this work, we report the nonprecious metal nickel-catalyzed lactamization reaction of 2-arylanilines with CO2 under redox-neutral conditions via C-H bond activation. The reaction displayed excellent functional group tolerance, providing various phenanthridinones with moderate to high yields.

Diastereoselective Synthesis of Dihydrobenzofuran Spirooxindoles and Their Transformation into Benzofuroquinolinones by Ring Expansion of Oxindole Core

A mild and efficient approach for the diastereoselective synthesis of dihydrobenzofuran spirooxindoles using 3-chlorooxindoles and imines is presented. This process involves a formal [4 + 1] annulation, yielding the product with excellent diastereoselectivity. Furthermore, a novel method for constructing benzofuroquinolinone scaffolds through the ring expansion of oxindoles has been established. This method involves a lactam ring expansion to the quinolinone skeleton. Besides, a one-pot procedure for creating benzofuroquinolinone scaffolds from 3-chlorooxindoles and imines is also provided.

EtOS2K as a C1 Source: Solvent- and Temperature-Controlled Selective Synthesis of Quinoline-2-thione and Quinoline-2-one Derivatives

Herein, we disclosed a highly chemoselective synthesis of quinoline-2-one and quinoline-2-thione derivatives using EtOS2K as the C1 source. Quinoline-2-one derivatives were synthesized selectively with NaCl as a catalyst in the solvent DMSO/H2O, while quinoline-2-thione derivatives were produced without the need for any catalyst in an environmentally friendly solvent EtOH/H2O. The reaction conditions were mild and had good functional group tolerance.

Shvo-Catalyzed Hydrogenation of CO2 in the Presence or Absence of Ionic Liquids for Tandem Reactions

Ionic liquids (ILs) have been widely used in transition metal-catalyzed processes, but the precise behavior of ILs and catalysts in these reactions is unknown. Herein, the role of ILs and the interaction pattern between Shvo's catalyst and ILs have been revealed with characterization by ¹H NMR and crystallography based on the catalytic hydrogenation of CO₂. ILs promote the dissociation of Shvo's catalyst and enhance the rate of production of CO. The CO that is produced is subsequently used in the tandem hydroformylation-reduction of alkenes to produce valuable alcohols. In the absence of ILs, formamides can be obtained by N-formylation of most primary or secondary amines.

Pd(II)/Lewis Acid Catalyzed Intramolecular Annulation of Indolecarboxamides with Dioxygen through Dual C-H Activation

Transition-metal ion catalyzed intramolecular dual C-H activation to construct polycyclic heteroarene skeletons is merited for its step and atom-economic advantages in organic synthesis. However, in most cases, stoichiometric oxidants, elevated temperature, and other harsh conditions were commonly faced for this reaction, which apparently block the synthetic applications. Herein, we report a Pd(II)/LA (LA: Lewis acid) catalyzed intramolecular dual C-H activation to construct indoloquinolinone derivatives under mild conditions with dioxygen as the sole oxidant. It was found that adding LA such as Sc³⁺ to Pd(OAc)₂ sharply improved its catalytic efficiency, whereas Pd(OAc)₂ alone was very sluggish. The activity improvement was attributed to the linkage of the Sc³⁺ cation to the Pd(II) species through a diacetate bridge that significantly enhanced the electrophilic properties of Pd(II) for dual C-H activation.

Access to quinolinones via DMAP-catalysed cascade reaction of 2-substituted benzoic acids with organic azides

Herein, we report a DMAP-catalysed Curtius rearrangement and intramolecular cyclisation cascade reaction of 2-substituted aryl carboxylic acids with organic azides for the first time. This protocol features simple operation, broad scope and metal-free conditions, furnishing a broad spectrum of biologically attractive heterocycles. The synthetic virtue of this reaction was demonstrated by gram-scale synthesis and applicability toward drug-like molecules.

Metal-Free N-H/C-H Carbonylation by Phenyl Isocyanate: Divergent Synthesis of Six-Membered N-Heterocycles

We disclose a method using phenyl isocyanate to synthesize carbonyl-containing N-heterocycles. The metal-free novel approach for both N-H and C-H carbonylation processes was successfully refined, delivering a range of synthetically valuable derivatives of quinazoline-2,4(1H,3H)-dione, 2H-benzo[e] [1,2,4] thiadiazin-3(4H)-one 1,1-dioxide, and pyrrolo[1,2-a] quinoxalin-4(5H)-one. The protocol features broad substrates with diverse reactions suitable for excellent yields, mild conditions, and good functional group compatibility. Moreover, the applicability of the reaction was characterized by gram-scale synthesis and synthetic transformations for drug molecules.

One-Pot Preparation of (NH)-Phenanthridinones and Amide-Functionalized [7]Helicene-like Molecules from Biaryl Dicarboxylic Acids

A one-pot transformation of biaryl dicarboxylic acids to (NH)-phenanthridinone derivatives based on a Curtius rearrangement and subsequent basic hydrolysis was developed. This method is also applicable for the preparation of optically active amide-functionalized [7]helicene-like molecules. Furthermore, aza[5]helicene derivatives with a phosphate moiety were isolated as a product of the Curtius rearrangement step in the case of substrates that bear chalcogen atoms. The stereostructures of these products, revealed by X-ray diffraction analysis, suggested that chalcogen-bonding and pnictogen-bonding interactions might contribute to their stabilization. The configurational stability of the helicene-like molecules and their chiroptical properties were further investigated.

Ni-Catalysed intramolecular reductive aminocarbonylation of 2-haloaryl-tethered nitroarenes for the synthesis of dibenzazepine-based heterocycles

A nickel-catalysed intramolecular reductive aminocarbonylation of 2-haloaryl-tethered nitroarenes is developed for rapid access to a variety of dibenzoazepinones and their derivatives.

Synthetic Strategies in the Preparation of Phenanthridinones

Phenanthridinones are important heterocyclic frameworks present in a variety of complex natural products, pharmaceuticals and displaying wide range of pharmacological actions. Its structural importance has evoked a great deal of interest in the domains of organic synthesis and medicinal chemistry to develop new synthetic methodologies, as well as novel compounds of pharmaceutical interest. This review focuses on the synthesis of phenanthridinone scaffolds by employing aryl-aryl, N-aryl, and biaryl coupling reactions, decarboxylative amidations, and photocatalyzed reactions.

Metal-Free C-H [5 + 1] Carbonylation of 2-Alkenyl/Pyrrolylanilines Using Dioxazolones as Carbonylating Reagents

A novel metal-free C-H [5 + 1] carbonylative annulation of 2-alkenyl/pyrrolylanilines with dioxazolones has been established for the assembly of the privileged quinolinones and pyrrolyl-fused quinoxalinones. Entirely differing from the existing reports, the dioxazolones herein behave with an innovative chemistry and first emerge as carbonylating reagents to participate in annulation reactions. Moreover, this process features exceedingly simple operation (only solvent) and tolerates both vinyl and aryl substrates. Comprehensive mechanistic studies indicate that the formed isocyanate intermediate plays a crucial role in enabling the carbonylation annulation.

Palladium-catalyzed [2 + 2 + 1] annulation: access to chromone fused cyclopentanones with cyclopropenone as the CO source

A variety of chromone fused cyclopentanones are efficiently generated in good to high yields via palladium-catalyzed [2 + 2 + 1] annulation, in which cyclopropenone was utilized for the first time as the sole CO surrogate in the carbonylation process.

Organocatalyst in Direct C(sp2)-H Arylation of Unactivated Arenes: [1-(2-Hydroxyethyl)-piperazine]-Catalyzed Inter-/Intra-molecular C-H Bond Activation

This article describes the identification of 1-(2-hydroxyethyl)-piperazine as a new, cost-effective, highly efficient organocatalyst, which promotes both inter- and intra-molecular direct C(_sp²)-H arylations of unactivated arenes in the presence of potassium tert-butoxide. While the inter-molecular C-H arylation of unactivated benzenes with aryl halides (Ar-X; X = I, Br, Cl) toward biaryl syntheses underwent smoothly in the presence of only 10 mol % organocatalyst, the intra-molecular C-H arylation catalytic system composed of 40 mol % each of the catalyst and the additive (4-dimethylaminopyridine (DMAP)). The novel catalyst was also able to perform both inter- and intra-molecular direct arylations simultaneously in a single pot. The mechanistic studies confirmed the involvement of aryl radical anions and proceeded via a single-electron-transfer (SET) mechanism. The large substrate scope, high functional group tolerance, competition experiments, gram-scale synthesis, and kinetic studies further highlight the importance and versatile nature of the methodology as well as the compatibility of the new catalyst. To the best of our knowledge, this is the first report on any organocatalyst that reported detailed investigations of both inter- and intra-molecular direct C(_sp²)-H arylations of unactivated arenes in a single representation.

Synthesis of Lactams via Ir-Catalyzed C-H Amidation Involving Ir-Nitrene Intermediates

x-membered lactams were synthesized via either an amidation of sp³ C-H bonds or an electrophilic substitution of arenes via Ir-nitrene intermediates. With the employment of a readily available iridium catalyst in dichloromethane or hexafluoro-2-propanol, a wide range of lactams were synthesized in good to excellent yields with high selectivity.

CO2 = CO + [O]: recent advances in carbonylation of C–H bonds with CO2

Carbon dioxide (CO₂) is an ideal one-carbon source owing to its nontoxicity, abundance, availability, and recyclability.

Catalytic formation of N3-substituted quinazoline-2,4(1H,3H)-diones by Pd(ii)EN@GO composite and its mechanistic investigations through DFT calculations

Modified GO based palladium composite was synthesized for catalytic synthesis of N3-substituted ouinazoline-2,4(1H,3H)-diones and the mechanistic route was theoretically investigated.

Palladium/copper-catalyzed multicomponent reactions of propargylic amides, halohydrocarbons and CO2 toward functionalized oxazolidine-2,4-diones

A palladium/copper-catalyzed oxy-carbonation of propargylic amides by halohydrocarbons and CO2 has been developed toward functionalized oxazolidine-2,4-diones. This multi-component reaction (MCR) was triggered by the oxidative addition of RX to Pd(0), followed by the sequential carboxylation of amide and trans-oxopalladation of an electron-deficient triple bond by RPdX species. Finally, the reductive elimination afforded products possessing tetra-substituted vinyl motifs and Pd(0). This protocol features simultaneous formation of three bonds, representing an efficient method for incorporation of CO2 into value-added heterocycles.

Concise and Efficient Synthesis of Indole-Indolone Scaffolds through MeOTf-Induced Annulation of N-(2-Cyanoaryl)indoles

MeOTf-triggered annulation of N-(2-cyanoaryl)indoles to provide indolo[1,2-a]indol-10-imines and the corresponding indolo[1,2-a]indol-10-ones have been described under metal-free conditions. A variety of functional groups are tolerated in their scaffolds with good to excellent yields. The reaction could be carried to gram scale.

Kolbe-Schmitt type reaction under ambient conditions mediated by an organic base

The combined use of an organic base for resorcinols realized a Kolbe-Schmitt type reaction under ambient conditions. When resorcinols (3-hydroxyphenol derivatives) were treated with DBU under a carbon dioxide atmosphere, nucleophilic addition to carbon dioxide proceeded to afford the corresponding salicylic acid derivatives in high yields.

C-H Bond Carboxylation with Carbon Dioxide

Carbon dioxide is a nontoxic, renewable, and abundant C₁ source, whereas C-H bond functionalization represents one of the most important approaches to the construction of carbon-carbon bonds and carbon-heteroatom bonds in an atom- and step-economical manner. Combining the chemical transformation of CO₂ with C-H bond functionalization is of great importance in the synthesis of carboxylic acids and their derivatives. The contents of this Review are organized according to the type of C-H bond involved in carboxylation. The primary types of C-H bonds are as follows: C(sp)-H bonds of terminal alkynes, C(sp² )-H bonds of (hetero)arenes, vinylic C(sp² )-H bonds, the ipso-C(sp² )-H bonds of the diazo group, aldehyde C(sp² )-H bonds, α-C(sp³ )-H bonds of the carbonyl group, γ-C(sp³ )-H bonds of the carbonyl group, C(sp³ )-H bonds adjacent to nitrogen atoms, C(sp³ )-H bonds of o-alkyl phenyl ketones, allylic C(sp³ )-H bonds, C(sp³ )-H bonds of methane, and C(sp³ )-H bonds of halogenated aliphatic hydrocarbons. In addition, multicomponent reactions, tandem reactions, and key theoretical studies related to the carboxylation of C-H bonds are briefly summarized. Transition-metal-free, organocatalytic, electrochemical, and light-driven methods are highlighted.

Recent advances in nucleophile-triggered CO2-incorporated cyclization leading to heterocycles

CO₂, as a sustainable, feasible, abundant one-carbon synthon, has been utilized in carboxylative cyclization, carbonylative cyclization, and reductive cyclization.

Palladium-catalyzed decarbonylative annulation of phthalimides with arynes: direct construction of phenanthridinones

A novel palladium-catalyzed decarbonylative annulation between phthalimides and arynes was well-established, affording phenanthridinone derivatives in moderate to good yields.

Nickel-Catalyzed Oxidative Decarboxylative Annulation for the Synthesis of Heterocycle-Containing Phenanthridinones

A nickel-catalyzed oxidative decarboxylative annulation reaction of simple benzamides and (hetero)aromatic carboxylates has been developed. This reaction provides access to a large array of phenanthridinones and their heterocyclic analogues, highlighting the utility and versatility of oxidative decarboxylative coupling strategies for C-C bond formation.

ROTf-induced annulation of heteroatom reagents and unsaturated substrates leading to cyclic compounds

The development of metal-free organic reactions is one of the hotspots in the synthesis of cyclic compounds. ROTf (alkyl trifluoromethanesulfonates), due to their good electrophilicity, are powerful alkylating reagents at heteroatoms such as nitrogen, oxygen, sulfur and phosphorus to induce an electrophilic centre for carbon-carbon or carbon-heteroatom bond formation. Inspired by this chemistry, a variety of research concentrating on heterocycles synthesis has been carried out. In this review, we mainly summarize the ROTf-induced annulation of heteroatom reagents such as nitriles, carbodiimides, azobenzenes, isothiocyanates, aldehydes, isocyanates and phosphaalkene with themselves or alkynes to afford cyclic compounds.

Transition Metal-Free CO2 Fixation into New Carbon-Carbon Bonds

CO₂ is the ultimate renewable carbon source on Earth and the essential C₁ building block for carbohydrate biosynthesis in photosynthetic organisms. Modern synthetic chemistry is facing the key challenge of developing fundamental transformations, such as C-C bond formation, in a sustainable and efficient manner from renewable sources. In this Minireview, the most significant methods recently reported for CO₂ fixation under transition metal-free conditions are summarized, organized into three different chapters according to the nature of the chemical transformation that forges the new C-C bond. The focus is on the mechanistic aspects of the different CO₂ activation modes, with specific attention to those systems that operate under catalytic conditions.

Catalytic Lactonization of Unactivated Aryl C-H Bonds with CO2: Experimental and Computational Investigation

The first catalytic lactonization of unactivated aryl C-H bonds with CO₂ to afford important phthalides is reported. Notably, this method features high selectivity, excellent functional group tolerance, smooth scalability, and facile product diversification. DFT calculations reveal that a novel insertion of two CO₂ into the O-Pd bond of a palladacycle might be the key step, providing great potential and a different perspective for carbonylation with CO₂.