Nickel-Catalyzed Regioselective Cross-Dehydrogenative Coupling of Inactive C(sp3)–H Bonds with Indole Derivatives

Ag-Catalyzed cross-dehydrogenative-coupling for the synthesis of 1,4-dioxan-2-yl substituted quinazoline hybrids in an aqueous medium

We herein developed an effective approach for the construction of 2- or 4-(1,4-dioxan-2-yl) substituted quinazolines under mild conditions. A silver-K2S2O8 catalyzed direct CDC reaction between quinazolines and 1,4-dioxane for the synthesis of a series of 2- or 4-(1,4-dioxan-2-yl) substituted quinazoline hybrids is reported. The reaction proceeded well in water under mild conditions and showed a broad substrate scope and good functional group compatibility.

Electroreductive Remote Benzylic C(sp3)-H Arylation of Aliphatic Ethers Using Cyanoarenes for the Synthesis of α-(Hetero)aryl Ethers

An iodoarene-driven electroreductive remote C(sp3)-H arylation of unsymmetrical 1-(o-iodoaryl)alkyl ethers with cyanoarenes for the site selective synthesis of α-(hetero)aryl ethers is developed. With the introduction of cyanoarenes as both aryl sources and electron transfer mediators, this method includes an iodoarene-driven strategy to enable the regiocontrollable formation of two new bonds, one C(sp2)-H bond, and one C(sp2)-C(sp3) bond, in a single reaction step through the sequence of halogen atom transfer (XAT), hydrogen atom transfer (HAT), radical-radical coupling, and decyanation.

Minisci-Type Dehydrogenative Coupling of N-Heteroaromatic Rings with Inert C(sp3)-H Enabled by a Visible-Light-Catalyzed Intermolecular Hydrogen Atom Transfer Process

The Minisci-type dehydrogenative coupling of N-heteroaromatic rings with inert C-H or Si-H partners via visible-light-catalyzed hydrogen atom transfer has been reported. This methodology allows the coupling reactions to be carried out in water as a solvent under air atmospheric conditions with visible-light illumination. A wide range of inert C-H and Si-H partners could be directly coupled with various N-aromatic heterocycles to deliver products in good to excellent yields.

A visible-light-induced bromine radical initiates direct C-H alkylation of heteroaromatics

Herein, a photoinduced direct C(sp2)-H alkylation of N-heteroaromatics by using commercially available tetrabutylammonium tribromide (TBATB) as a HAT reagent is described. The method uses O2 as the oxidant, and features metal-free, mild reaction conditions and good functional group compatibility.

Copper-Catalyzed Synthesis of N-Fused Quinolines via C(sp3)-H Activation-Radical Addition-Cyclization Cascade

A novel copper-catalyzed cyclization reaction for the synthesis of pyrazolo[1,5-a]quinoline, triazolo[1,5-a]quinoline, and pyrrolo[1,2-a]quinoline derivatives is described. The process is initiated by di-tert-butyl peroxide-mediated C(sp3)-H activation to generate the α-functionalized radical, which supervenes a cascade radical addition/cyclization sequence to access the N-fused quinolines in good yields with broad functional group tolerance.

Non-noble metal-catalyzed cross-dehydrogenation coupling (CDC) involving ether α-C(sp3)-H to construct C-C bonds

Ether derivatives are widespread as essential building blocks in various drugs, natural products, agrochemicals, and materials. Modern economy requires developing green strategies with improved efficiency and reduction of waste. Due to its atom and step-economy, the cross-dehydrogenative coupling (CDC) reaction has become a major strategy for ether functionalization. This review covers C-H/C-H cross-coupling reactions of ether derivatives with various C-H bond substrates via non-noble metal catalysts (Fe, Cu, Co, Mn, Ni, Zn, Y, Sc, In, Ag). We discuss advances achieved in these CDC reactions and hope to attract interest in developing novel methodologies in this field of organic chemistry.

Visible light-induced direct alkylation of the purine C8-H bond with ethers

The one-step visible light-induced direct alkylation of the C₈-H bond for purine derivatives by ethers was developed using Eosin Y as the photocatalyst and t-BuOOH as the oxidant at room temperature. This method describes the coupling of the α-C of the ether to the C₈ of purine. Of particular interest is that substrates include purines with various functional groups and even unprotected 9H-purines. The protocol provides an effective method for the synthesis of 8-alkylpurine derivatives with high atom economy and high regioselectivity.

DTBP-mediated cross-dehydrogenative coupling of 3-aryl benzofuran-2(3H)-ones with toluenes/phenols for all-carbon quaternary centers

We have developed a transition-metal free protocol for efficient cross-dehydrogenative coupling of 3-aryl benzofuran-2(3H)-ones and toluenes/phenols using DTBP as an oxidant. A diverse range of 3-aryl benzofuran-2(3H)-ones, toluenes, and phenols undergo C-H bond cleavage to generate all-carbon quaternary centers in good yields, making this protocol useful for the synthesis of complex molecules. A gram scale experiment was performed in good yield.

Microwave-accelerated and benzoyl peroxide (BPO)-initiated cyclization of 1,5-enynes having cyano groups with cyclic alkanes under metal-free conditions

A novel and efficient method for preparing exocyclic indan derivatives, with this method involving benzoyl peroxide (BPO)-initiated cyclization of 1,5-enynes having cyano groups with simple cyclic alkanes under microwave irradiation, has been developed. The presented approach showed advantages of simple conditions, an environmentally friendly protocol, good functional-group tolerance, and high yields of products.

Three-component synthesis of α-indole-β-sulfonyl tetrahydrofurans under metal-free conditions

An efficient multi-component reaction has been developed for the synthesis of 2,3-disubstituted tetrahydrofurans in a “one pot” manner, starting from readily available 2-arylindoles, arylsulfonyl azides, and tetrahydrofuran under simple and easily operated reaction conditions.

Electrochemical Regioselective Cross-Dehydrogenative Coupling of Indoles with Xanthenes

An electrochemical cross-dehydrogenative coupling of indoles with xanthenes has been established at room temperature. This coupling reaction could proceed in the absence of any catalyst or external oxidant, and generate the indole derivatives in moderate yields. Mechanistic experiments support that a radical pathway maybe involved in this reaction system.

Copper-Catalyzed Direct Allenylation of Inactive Cyclic Ethers

We report here a direct allenylation reaction of inactive cyclic ethers. The reaction proceeds through a copper-catalyzed 1,4-difunctionalization of 1,3-enynes, with cyano group installed at the allenes simultaneously. This methodology shows a broad functional group compatibility to 1,3-enynes. Diversified allene-modified cyclic ether derivatives were synthesized with high regioselectivity under mild conditions.

Metal-free visible-light-promoted C(sp3)-H functionalization of aliphatic cyclic ethers using trace O2

Presented is a light-promoted C-C bond forming reaction yielding sulfone and phosphate derivatives at room temperature in the absence of metals or photoredox catalyst. This transformation proceeds in neat conditions through an auto-oxidation mechanism which is maintained through the leaching of trace amounts of O2 as sole green oxidant.

Heteroarylation of Ethers, Amides, and Alcohols with Light and O2

An efficient protocol for the C_α-H heteroarylation of ethers, amides, and alcohols using air and light under mild conditions is described. The reaction is applicable to a wide spectrum of functional groups. The generation of C-radicals via photoinduced aerobic oxidation of ethers, amides, and alcohols is the key feature of the process. Control experiments suggest a radical pathway for the reaction.

External oxidant-free alkylation of quinoline and pyridine derivatives

A novel and efficient method for the generation of alkyl radicals and the alkylation of quinoline and pyridine derivatives under mild conditions has been developed. This strategy allows the direct alkylation of heteroaromatics in the absence of an external oxidant. A preliminary mechanistic study suggests that the present reaction probably proceeds via an intermolecular HAT process.

Base-promoted domino radical cyclization of 1,6-enynes

A good regioselective, high atom-economical and transition-metal-free method for the synthesis of α-functionalized ether derivatives via the domino radical cyclization of 1,6-enynes is described. A series of α-functionalized ether derivatives could be easily obtained in good yields with wide functional group tolerance by using less toxic and inexpensive Cs₂CO₃ as the base. The control experiment results show that the reaction involves a radical process. This strategy provides a regioselective way toward the formation of dual C-C bonds in one step.

Graphene oxide as a green carbon material for cross-coupling of indoles with ethers via oxidation and the Friedel–Crafts reaction

The first example of using GO as a carbon material facilitated C(sp²)–C(sp³) bond formation.

The controllable C2 arylation and C3 diazenylation of indoles with aryltriazenes under ambient conditions

The controllable C2 arylation and C3 diazenylation of indoles with aryltriazenes under ambient conditions was investigated.

Nickel-Catalyzed Cross-Dehydrogenative Coupling of α-C(sp3)-H Bonds in N-Methylamides with C(sp3)-H Bonds in Cyclic Alkanes

A nickel-catalyzed cross-dehydrogenative coupling reaction of α-C(sp³)-H bonds in N-methylamides with C(sp³)-H bonds from cyclic alkanes has been developed, which offers a cheap transition-metal-catalyzed C-H activation method for amides without the requirement for any extraneous directing group. This new strategy is highly selective and tolerates a variety of functional groups. Mechanistic investigations into the reaction process are also described in detail.

Metal- and Acid-Free C-H Formylation of Nitrogen Heterocycles: Using Trioxane as an Aldehyde Equivalent Enabled by an Organic-Soluble Oxidant

A metal-free, innate, and practical C-H formylation of nitrogen heterocycles using trioxane as a formyl equivalent is reported. This reaction provides a mild and robust method for modifying medicinally relevant heterocycles with an aldehyde handle. The use of an organic soluble oxidant, tetrabutylammonium persulfate, is critical in promoting the desired coupling.

Electrochemical Synthesis of Bisindolylmethanes from Indoles and Ethers

An electrochemical bisindolylation of ethers was developed. Carried out under ambient conditions and in the absence of any chemical oxidants, this reaction exhibits a broad substrate scope and good functional group compatibility.

Versatile cross-dehydrogenative coupling of heteroaromatics and hydrogen donors via decatungstate photocatalysis

A facile sunlight-induced derivatization of heteroaromatics via photocatalyzed C-H functionalization in amides, ethers, alkanes and aldehydes is described. Tetrabutylammonium decatungstate (TBADT) was used as the photocatalyst and allowed to carry out the process under mild conditions.

Transition-metal-free direct C-3 alkylation of quinoxalin-2(1H)-ones with ethers

An efficient protocol for the synthesis of 3-alkyl quinoxalin-2(1H)-ones has been developed via the transition-metal-free cross-coupling reaction of quinoxalin-2(1H)-ones with ethers with moderate to good yields under relatively mild conditions.

Peroxy mediated Csp2–Csp3 dehydrogenative coupling: regioselective functionalization of coumarins and coumarin-3-carboxylic acids

Regioselective functionalization of coumarins/coumarin carboxylic acids at C-3 via activation of Csp³–H bonds of ethers under metal-free conditions is developed.

Copper-catalyzed α-C–H amidation of simple ethers through C(sp3)–H/N–H cross dehydrogenative coupling

An efficient copper-catalyzed α-C–H amidation of simple ethers with N-(8-quinolyl)amides through C(sp³)–H/N–H cross dehydrogenative coupling was developed.

Copper-catalyzed oxidative intermolecular 1,2-alkylarylation of styrenes with ethers and indoles

A new copper-catalyzed oxidative three-component intermolecular 1,2-alkylarylation of styrenes with ethers and indoles is disclosed.