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.

Manganese(I)-catalyzed nucleophilic addition of C(sp3)-H bonds to aldehydes.

The C-H bond activation catalyzed by a manganese(I) complex has achieved significant development but is limited to C(sp2)-H bonds. In this work, an efficient manganese(I)-catalyzed direct nucleophilic addition reaction of C(sp3)-H bonds to aromatic aldehydes has been developed. This is the first example of manganese(I)-catalyzed C(sp3)-H bond transformation. A manganacycle complex was isolated and proved to be the key active intermediate in the catalytic cycle.

Copper-Catalyzed C4-selective Carboxylation of Pyridines with CO2 via Pyridylphosphonium Salts.

Pyridine motifs are widespread pharmacophores in many drugs. Installing various substituents through pyridine C-H bond functionalization is significant for new drug design and discovery. Developments of late-stage functionalization reactions enrich the strategies for selective functionalization of pyridines. However, late-stage C-H carboxylation of pyridines is a long-standing challenge, especially selectively carboxylation with CO2 on pyridine motifs. Herein, we describe a practical method for C4-H carboxylation of pyridines via one-pot C-H phosphination and copper-catalyzed carboxylation of the resulted phosphonium salts with CO2 . The reaction is conducted under mild conditions and compatible with multiple active groups and several pyridine drugs, providing diverse valuable isonicotinic acid compounds, demonstrating the application potential of this strategy.

Diethylzinc-promoted carboxylation of aryl/alkenyl boronic acids with CO2.

The carboxylation of aryl and alkenyl boronic acids with CO2 is rarely studied and only achieved using copper salts as the catalyst in the presence of a strong base. Herein, we report a diethylzinc-promoted carboxylation of aryl or alkenyl boronic acids with carbon dioxide. The reaction does not require a transition-metal catalyst, and has simple and mild conditions and a broad substrate scope.

Cascade C-H Activation and Defluorinative Annulation of 2-Arylbenzimidazoles with α-Trifluoromethyl-α-diazoketones: Modular Assembly of 6-Fluorobenzimidazo[2,1-a]isoquinolines.

A novel Ru-catalyzed redox-neutral [4+2] cyclization of 2-arylbenzimidazoles with α-trifluoromethyl-α-diazoketones has been achieved through sequential C-H activation and defluorinative annulation. This synthetic protocol unlocks modular and expeditious access to 6-fluorobenzimidazo[2,1-a]isoquinolines with high efficiency and excellent functional group compatibility. The resultant monofluorinated heterocyclic products can readily diversified by various nucleophiles.

Dimeric Manganese-Catalyzed Direct Nucleophilic Addition of C(sp2)-H Bonds to Inert Aldehydes.

An efficient direct nucleophilic addition reaction of C(sp2)-H bonds to aldehydes catalyzed by a dimeric manganese has been developed. This reaction has a broad range of substrates, and high yields were also obtained with inert aliphatic aldehydes as substrates. A dimeric Mn2(CO)8Br2 was proven to be a more efficient catalyst precursor than the monomeric Mn(CO)5Br.

Ruthenium(II)-Catalyzed Grignard-Type Nucleophilic Addition of C(sp2)-H Bonds to Unactivated Aldehydes.

The Grignard-type nucleophilic addition of C(sp2)-H bonds to aldehydes catalyzed by high-oxidation-state transition metal complexes is limited to activated aldehydes. Herein, we report the first example of Grignard-type nucleophilic addition of C(sp2)-H bonds to unactivated aldehydes catalyzed by high-oxidation-state ruthenium(II). The reaction has mild reaction conditions and good functional group tolerance. The corresponding alcohol products are obtained in good to excellent yields.

Copper-Catalyzed Carboxylation of Aryl Thianthrenium Salts with CO2.

Carboxyl group is one of the most widely used groups in organic synthesis. Herein, an efficient copper-catalyzed carboxylation of aryl thianthrenium salts with carbon dioxide (CO2 ) at room temperature has been developed. The reaction employs low loading of cuprous chloride catalyst under 1 atm CO2 and exhibits good functional group tolerance. In combination with C-H thianthrenation of aromatic hydrocarbons, this work provides an efficient method for the site-selective C-H carboxylation of aromatic hydrocarbons. It may serve as a significant late-stage carboxylation tool for the modification of drug molecules in the future.

Access to 5-fluoroalkylated trisubstituted oxazoles via copper-catalyzed cyclization of α-fluoroalkyl-α-diazoketones with amides.

A novel copper-catalyzed cyclization of α-fluoroalkyl-α-diazoketones with (thio)amides has been developed. This mechanistically distinct protocol provides a robust and straightforward approach to construct 5-fluoroalkylated trisubstituted oxazoles and thiazoles with high efficiency and excellent functional group compatibility. Experimental studies suggest a mechanism involving imidate ligand migratory insertion of a copper carbenoid as the key step.

Rhodium-catalyzed denitrogenative gem-difunctionalization of pyridotriazoles with thioesters: formal carbene insertion into C(O)-S bonds.

A formal carbene insertion into C(O)-S bonds to access α-quaternary pyridines was achieved via a rhodium(II)-catalyzed in situ formation of sulfonium ylides from pyridotriazoles with thioesters followed by acyl group migration. This protocol has enabled an efficient denitrogenative gem-acylthiolation of pyridotriazoles to incorporate an acyl, pyridyl, and sulfur-substituted quaternary carbon center with high selectivity, broad substrate scope, and good functional group tolerance.

Cobalt-catalyzed carboxylation of aryl and vinyl chlorides with CO2.

The transition-metal-catalyzed carboxylation of aryl and vinyl chlorides with CO2 is rarely studied, and has been achieved only with a Ni catalyst or combination of palladium and photoredox. In this work, the cobalt-catalyzed carboxylation of aryl and vinyl chlorides and bromides with CO2 has been developed. These transformations proceed under mild conditions and exhibit a broad substrate scope, affording the corresponding carboxylic acids in good to high yields.

Silver-Catalyzed Activation of Pyridotriazoles for Formal Intramolecular Carbene Insertion into Vinylic C(sp2)-H Bonds.

A silver-catalyzed intramolecular denitrogenative annulation of pyridotriazole with alkene was reported to achieve the challenging carbene insertion into the vinylic C(sp2)-H bond. This protocol has enabled the construction of functionalized 1H-indenes with high efficiency and excellent functional group tolerance. Experimental and computational studies suggest a stepwise mechanism involving a water-promoted hydrogen atom transfer with the aid of a silver catalyst.

Ni-Catalyzed Direct Carboxylation of an Unactivated C-H Bond with CO2.

The transition-metal-catalyzed direct carboxylation of an unactivated C-H bond is rarely reported, and no example of catalysis using abundant and cheap nickel has been reported. In this work, the first Ni-catalyzed direct carboxylation of an unactivated C-H bond under an atmospheric pressure of CO2 is reported. This method affords moderate to high carboxylation yields of various methyl carboxylates under mild conditions. Preliminary mechanistic studies reveal that a Ni(0)-Ni(II)-Ni(I) catalytic cycle may be involved in this reaction.

The regioselective annulation of alkylidenecyclopropanes by Rh(iii)-catalyzed C-H/C-C activation to access spirocyclic benzosultams.

Functionalized benzosultams are an essential class of structural motif found in various biologically active molecules. The synthesis of spirocyclic benzosultams from N-sulfonyl ketimine and alkylidenecyclopropanes (ACPs) under the catalysis of Rh(iii) has been developed. This transformation enables the formation of two C-C bonds and a double bond with high E-selectivity through C-H and C-C bond activation. This reaction proceeded smoothly with excellent regioselectivity, high efficiency, and tolerance for various functional groups.

RhIII-Catalyzed Synthesis of Cyclopenta[b]carbazoles via Cascade C-H/C-C Bond Cleavage and Cyclization Reactions: Using Amide as a Traceless Directing Group.

Rhodium-catalyzed cascade C-H/C-C cleavage and cyclization reactions of 3-amide substituted indoles with diynes to construct cyclopenta[b]carbazoles have been developed. A strategy amide worked as a novel traceless directing group along with C-C bond cleavage via Friedel-Crafts-retro reaction has been disclosed in this protocol. This method exhibits a broad substrate scope and tolerates various functional groups, furnishing the carbazole derivatives in good to high yields.

Sulfhydryl-Directed Iridium-Catalyzed C-H/Diazo Coupling and Tandem Annulation of Naphthalene-1-thiols.

The first sulfhydryl-directed iridium-catalyzed C-H/diazo coupling and tandem annulation of naphthalene-1-thiols has been developed. The framework of naphtho[1,8-bc]thiopyrans was constructed in a one-step reaction with good yields. This transformation provides a practical synthetic route for the widely used naphtho[1,8-bc]thiopyran derivatives.

Cp*Co(III)-Catalyzed Regioselective Synthesis of Cyclopenta[ b]carbazoles via Dual C(sp2)-H Functionalization of 1-(Pyridin-2-yl)-indoles with Diynes.

Cp*Co(III)-catalyzed synthesis of cyclopenta[ b]carbazoles from 1-(pyridin-2-yl)-indoles and diynes is developed. This reaction involves dual C-H activation of indoles and domino cyclizations with diynes and has excellent regioselectivity, high efficiency, a broad substrate scope, and tolerance for various functional groups. A series of cyclopenta[ b]carbazole molecular scaffolds are obtained in good to excellent yields.

Annulation of ß-Enaminonitriles with Alkynes via RhIII-Catalyzed C-H Activation: Direct Access to Highly Substituted 1-Naphthylamines and Naphtho[1,8- bc]pyridines.

A Cp*RhIII-catalyzed oxidative annulation of ß-enaminonitriles with alkynes was reported to achieve selective synthesis of polysubstituted 1-naphthylamines and naphtho[1,8- bc]pyridines via multiple C-H activations. Assisted by a naphthylamine NH2 group, 1-naphthylamines were also readily cyclized to produce naphtho[1,8- bc]pyridines. In addition, the obtained naphtho[1,8- bc]pyridine derivatives exhibit intense fluorescence in the solid state.

Cp*Co(III)-Catalyzed C-H Acylmethylation of Arenes by Employing Sulfoxonium Ylides as Carbene Precursors.

A Cp*Co(III)-catalyzed C-H bond functionalization of a range of arenes by employing sulfoxonium ylides as carbene precursors instead of diazo compounds and other carbene precursors has been established. This reaction is highly efficient without any additive, possesses high step and atom economies, and tolerates a range of functional groups.

Synthesis of Cinnolines and Cinnolinium Salt Derivatives by Rh(III)-Catalyzed Cascade Oxidative Coupling/Cyclization Reactions.

A novel method for the synthesis of cinnolines and cinnolinium salt derivatives via Rh(III)-catalyzed cascade oxidative coupling/cyclization reaction from Boc-arylhydrazines and alkynes has been developed. The reactions have a broad substrate scope and high stereoselectivity with readily available starting materials and provides an efficient synthetic route for this kind of compounds. A catalytically competent five-membered rhodacycle has been isolated, thus revealing a key intermediate in the catalytic cycle.