Highly Regioselective α‐Arylation of Coumarins via Palladium‐Catalyzed C?H Activation/Desulfitative Coupling

A novel regioselective α‐arylation of coumarins with readily available arenesulfonyl chlorides and sodium arenesulfinates via palladium‐catalyzed direct C H functionalizations under mild reaction conditions is described. This protocol presents an unexpected and highly regio‐controlled arylation of coumarins at C‐3 to construct interesting 3‐arylcoumarins with fascinating biological and fluorescent properties. The regioselectivity observed is in sharp contrast with that expected for the Heck reactions.

     

Easy Access to 1‐Amino and 1‐Carbon Substituted Isoquinolines via Cobalt‐Catalyzed C?H/N?O Bond Activation

A green atom‐economical method for the synthesis of highly functionalized 1‐amino and 1‐carbon substituted isoquinolines from the reaction of N′‐hydroxybenzimidamides and aryl ketoximes, respectively, with alkynes via pentamethylcyclopentadienylcobalt(III)‐catalyzed C H/N O bond activation is described. The external oxidant‐free annulation reaction uses the =NOH moiety in N′‐hydroxybenzimidamides or N‐aromatic ketone oximes as the directing group and internal oxidant. This first row transition metal‐catalyzed annulation serves as an efficient alternative for the synthesis of isoquinolines, as water is the only by‐product and expensive noble metals such as rhodium(III), iridium(III), palladium(II), and ruthenium(II) are not required. The reaction proceeds via C H activation, alkyne insertion, reductive elimination, and N O activation.

     

Transition Metal‐Catalyzed C?H Activation of Indoles

The last decades have seen a tremendous expanse in the application of C H activation of many different substrate classes, including the invaluable indole scaffold. Following the exciting emergence of C H activation as a multi‐faceted platform for functionalization, a versatile tool box has been developed for the preparation of structurally diverse indoles. This review article discusses recent advances and strategies for transition metal‐catalyzed C H activation of indoles.

     

Copper‐Catalyzed Synthesis of α‐Thioaryl Carbonyl Compounds Through S?S and C?C Bond Cleavage

A method to access α‐thioaryl ketones and α‐thioaryl esters employing copper acetate (hydrate) as catalyst and readily accessible diaryl disulfides and β‐diketones (or β‐keto esters) has been developed. Both alkyl‐ and aryl‐substituted carbonyl compounds can be prepared.

     

Mechanistic Switch via Subtle Ligand Modulation: Palladium‐Catalyzed Synthesis of α,β‐Substituted Styrenes via C?H Bond Functionalization

A new catalyst system able to efficiently perform the synthesis of styrenes via C H bond functionalization and a subtle ligand modification are described. The high level of activity achieved allows for the synthesis of highly functionalized α,β‐substituted styrenes, even the elusive E‐configured trisubstituted olefins, in a regio‐ and stereoselective manner. Mechanistic experiments allowed for the identification of the corresponding synthetic intermediates.     

Iron‐Catalyzed Esterification of Benzyl C?H Bonds to Form α‐Keto Benzyl Esters

An atom‐economic and efficient non‐precious metal‐catalyzed esterification of benzyl C H bonds has been developed. A variety of α‐keto benzyl esters have been accessed in good yields through the reactions between benzyl derivatives and benzoylformic acids using iron trifluoride as a catalyst in the presence of di‐tert‐butyl peroxide under an inert atmosphere. This strategy provides a straightforward access to linearly expanded α‐keto benzyl esters. A plausible reaction mechanism is proposed.

     

Ruthenium‐Catalyzed Remote Electronic Activation of Aromatic C?F Bonds

The tandem isomerization and nucleophilic aromatic substitution of allylic fluoro‐substituted benzylic alcohols is described for the first time. In the presence of the ruthenium complex Ru(PPh₃)₃(CO)(H)₂, 1‐(4‐fluorophenyl)prop‐2‐en‐1‐ol is converted into the corresponding para‐amino ketone or para‐phenolic substituted ketone.     

Lewis Acid‐Catalyzed Generation of C?C and C?N Bonds on π‐Deficient Heterocyclic Substrates

Focused microwave irradiation of a series of halogenated nitrogen heterocycles and different kinds of nucleophiles in the presence of a catalytic amount of indium trichloride leads to the efficient and completely regioselective generation of aromatic C C and C N bonds. The method is simple, rapid, general and inexpensive, and can be performed without the use of dried solvents. Most of the synthetized compounds are new and in many cases the work‐up required only filtration. Furthermore, this is the first example of the use of a Lewis acid as a catalyst for heteroarylation, vinylation and amination reactions on π‐deficient heterocyclic substrates.

     

Rhodium‐Catalyzed Tandem Annulation Reactions of 7‐Azaindoles with Electron‐Deficient Olefins via Double C?H Activation

Rhodium‐catalyzed tandem annulation reactions via olefination and subsequent intramolecular C‐Michael‐type cyclization represent an efficient approach for the direct construction of C C bonds. The simple and atom‐economic strategy produces various alkylation derivatives of 7‐azaindole with a quaternary carbon center from 7‐azaindoles and olefins.

     

Grignard‐Type Arylation of Aldehydes via a Rhodium‐Catalyzed C?H Activation under Mild Conditions

An efficient Grignard‐type arylation of aldehydes via aryl C H activation was achieved under mild conditions catalyzed by rhodium. The reaction provides an easy access to a wide variety of benzyl alcohols and can tolerate various functional groups as well as air and water.     

Zinc‐Catalyzed Organic Synthesis: C?C,C?N,C?O Bond Formation Reactions

Zinc is the 24^th most abundant element in the Earth’s crust. Since the discovery of pure zinc metal in the 18^th century, the main application of zinc metal is as materials. Because zinc salts are abundant, cheap, non‐toxic, and exhibit environmentally benign properties, organic chemists have been interested in using zinc salts as catalysts in organic synthesis during the last three decades. Within this review, we have summarized the progress on applications of zinc salts in organic reactions. Our the target is to emphasize the special properties of zinc catalysts, and further promote the interest of organic chemists.     

Synthesis of [60]Fullerene‐Fused Tetralones via Palladium‐ Catalyzed Ketone‐Directed sp2 C?H Activation and sp3 C?H Functionalization

The palladium‐catalyzed ketone‐directed dual sp² C H activation and sp³ C H functionalization has been applied for fullerene functionalization for the first time. The sec‐alkyl aryl ketones have been exploited to react with [60]fullerene (C₆₀) to provide the novel and scarce C₆₀‐fused tetralones. The combined use of a highly active cationic palladium(II) catalyst and trifluoromethanesulfonic acid is crucial for the improvement of the reaction yield. A plausible reaction mechanism leading to the observed products has been proposed, and the electrochemistry of the fullerene products has also been investigated.

     

Iron‐Catalyzed C?H Fuctionalization of Indoles

An easily available iron catalyst was developed to accomplish the C H functionalization of indoles with α‐aryl‐α‐diazoesters in high yields under mild conditions. The asymmetric C H functionalization of indoles was also realized by using iron complexes of chiral spiro bisoxazolines with up to 78% ee.     

Nickel‐Catalyzed Cross‐Coupling of Arene‐ or Heteroarenecarbonitriles with Aryl‐ or Heteroarylmanganese Reagents through C?CN Bond Activation

The nickel‐catalyzed cross‐coupling reaction of arene‐ or heteroarenecarbonitriles with aryl‐ or heteroarylmanganese reagents via C CN bond activation has been developed. Both electron‐rich and electron‐deficient nitriles can be employed as the electrophilic substrates. The reaction tolerates a range of functional groups and aromatic heterocycles.     

Palladium‐Catalyzed Oxidative Intramolecular C?C Bond Formation via Double sp2 C?H Activation between the 2‐Position of Imidazoles and a Benzene Ring

Oxidative intramolecular C C bond formation via double sp² C H activation between the 2‐position of imidazoles and a benzene ring catalyzed by palladium(II) has been developed, which provides an atom‐economical, concise and efficient methodology to synthesize imidazole‐ or benzimidazole‐fused isoquinoline polyheteroaromatic compounds.     

Diruthenium(I,I) Catalysts for the Formation of β‐ and γ‐Lactams via Carbenoid C?H Insertion of α‐Diazoacetamides

Intramolecular carbenoid C H insertion of five α‐diazoacetamides [N₂CH CONR₂, NR₂=NEt₂ ( 3a ), NBu₂ ( 3b ), N(i‐Pr)₂ ( 3c ), N(CH₂Ph)₂ ( 3d ), N(i‐Pr)(CH₂Ph) ( 3e )], was investigated using as catalysts dinuclear Ru(I,I) complexes of the type [Ru₂(μ‐L¹)₂(CO)₄L²₂], where L¹ is a bidentate bridging acetate, calix[4]arenedicarboxylate, saccharinate, pyridin‐2‐olate, or triazenide ligand, as well as [RuCl₂(p‐cymene)]₂. The Ru(I,I) complexes were found to be suitable catalysts for the carbenoid cyclization reactions, except in the case of 3a . With diazoamides 3b–e , [Ru₂(μ‐sac)₂(CO)₅]₂ (sac=saccharinate) and [Ru₂(μ‐6‐chloropyridin‐2‐olate)₂(CH₃CN)₂(CO)₄] are as effective as Rh₂(OAc)₄ under the same conditions, although some differences in the regioselectivity and chemoselectivity of the cyclization are observed. The carbenoid cyclization reactions yield γ‐lactams from diazoamides 3a and 3b , both a β‐ and a γ‐lactam from 3c , and a β‐lactam as well as a 3‐azabicyclo[5.3.0]deca‐5,7,9‐trien‐2‐one from 3d . With 3e , formation of γ‐lactam 21 and of bicyclic lactam 23 prevails.     

C?C Bond Formation via C?H Activation and C?N Bond Formation via Oxidative Amination Catalyzed by Palladium‐ Polyoxometalate Nanomaterials Using Dioxygen as the Terminal Oxidant

An efficient heterogeneous palladium‐polyoxometalate catalyst with the formula Pd‐H₆PV₃Mo₉O₄₀/C has been successfully developed for carbon‐carbon (C C) bond formation via carbon‐hydrogen (C H) activation and carbon‐nitrogen (C N) bond formation via oxidative amination using oxygen as the terminal oxidant. The coupling processes are simple, and use relatively mild conditions to form the desired products. In addition, less waste is generated as no additional reagents such as organic/inorganic oxidants are required, and water is the only by‐product generated.     

Ruthenium(II)‐Catalyzed Oxidative Annulation Reactions of Arylimidazolium Salts via N‐Heterocyclic Carbene‐Directed C?H Activation

An efficient ruthenium(II)‐catalyzed oxidative annulation reaction of various arylimidazolium salts with alkynes via N‐heterocyclic carbene‐directed C H activation to obtain substituted benzo[ij]imidazo[2,1,5‐de]quinolizinium salts is reported. This catalytic reaction proceeds in an excellent regioselective manner when using unsymmetrical alkynes as reactants. The intermediate mono‐annulated products can be obtained by reducing the amount of catalyst. Two catalytically competent N‐heterocyclic carbene‐based cyclometallated ruthenium(II) complexes have been isolated and characterized, which represent the key intermediates in the catalytic cycle. Moreover, most of the products show a strong fluorescent property, indicating their potential for making new light‐emitting materials.

     

C?H Functionalization of Enamides: Synthesis of β‐Amidovinyl Sulfones via Visible‐Light Photoredox Catalysis

A mild, practical and environmentally friendly strategy to prepare β‐amidovinyl sulfones has been developed based on the sulfonation of enamides or enecarbamates via visible‐light photoredox catalysis. Direct C H functionalizations of enamides or enecarbamates under the optimized conditions proceeded with a wide scope of substrates and remarkable selectivity to give functionalized vinyl sulfones with good to excellent yields.     

Transition Metal‐Free Intermolecular α‐C?H Amination of Ethers at Room Temperature

We describe a new method for the intermolecular amination of the α‐C H bonds of ethers. A hypervalent iodine reagent was used as oxidant to enable the amination of cyclic and acyclic alkyl ethers with a wide range of amides, imides, and amines. The amination occurred at room temperature and without a transition metal catalyst. The method could be used to synthesize the anti‐cancer prodrug Tegafur and its analogues.