Biomimetic Aerobic C?H Olefination of Cyclic Enaminones at Room Temperature: Development toward the Synthesis of 1,3,5‐Trisubstituted Benzenes

A green and mild protocol for the dehydrogenative olefination of cyclic enaminones was devised via palladium catalysis at room temperature using oxygen as the terminal oxidant. The synthetic utility of the olefinated cyclic enaminones afforded a series of unique 1,3,5‐trisubstituted benzenes via an unanticipated Diels–Alder tandem reaction. The broad substrate scope and good yields achieved with this new protocol provide an alternative pathway for arene functionalization.

     

Palladium‐Catalyzed Oxidative sp2 C?H Bond Acylation with Aldehydes

An efficient method was developed for the direct acylation of arene sp² C H bonds with aldehydes using palladium acetate as catalyst and peroxide as oxidant. The solvent‐free oxidative acylation reaction assisted by a pyridine directing group provides an easy access to aromatic, aliphatic, and optical active ketones.     

Copper(II) Triflate‐Catalyzed Aerobic Oxidative C?H Functionalization of Glycine Derivatives with Olefins and Organoboranes

An economical, and practical copper(II) triflate‐catalyzed aerobic oxidative C H functionalization of glycine derivatives with olefins and organoboranes has been established. The mild reaction has an excellent functional group tolerance, and exhibits a broad scope with respect to both glycine derivatives and the two types of nucleophilic components, allowing for the facile synthesis of diverse substituted quinolines and glycine derivatives bearing various patterns of functionalities in the α‐position.

     

Tandem Catalysis: Alcohol Oxidation and C?C Bond Formation via C?H Bond Activation

A tandem process involving oxidation of a benzylic alcohol functionality followed by hydroarylation is described. These two atom‐economic sequences are very convenient to access functionalized aromatic ketones, using simple ruthenium trichloride as catalyst precursor. Moreover they appear to be highly compatible, tolerant, and selective toward various functional groups, and the ease of the protocol should make it very convenient for synthetic purposes.     

Mechanistic Insights into Enantioselective C?H Photooxygenation of Aldehydes via Enamine Catalysis

Organocatalytic photooxygenation of aldehydes at the α‐position proceeds via enamine catalysis, though enamines should be easily oxidized by singlet oxygen respectively to amides and carbonyl compounds. Moreover, the formation of a zwitterionic enamine peroxide intermediate was postulated based on experimental and theoretical data. The reaction affords desired diols (after in situ reduction) in a decent yield and (S)‐ or (R)‐enantioselectivity depending on a catalyst used. The (S)‐enantiomer predominated in imidazolidinone‐catalyzed reactions, while prolineamides assured the formation of the (R)‐stereoisomer. DFT calculation suggests that the enamine–oxygen complex with the lowest energy has the E, s‐cis conformation for the prolineamide derivative and E, s‐trans for the imidazolidinone catalyst, explaining the opposite stereoselectivity in the photooxygenation reaction.

     

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.     

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.

     

Copper‐Catalyzed Aerobic Oxidative Synthesis of 5‐Substituted Imidazo/Benzimidazoquinazolinones through Intramolecular C?H Amination

A simple and efficient copper‐catalyzed aerobic oxidative method for the synthesis of imidazo/benzimidazoquinazolinones has been developed through direct intramolecular C H amination of (1H‐imidazol‐1‐yl)[2‐(alkylamino)phenyl]methanones, and the corresponding target products were obtained in moderate to good yields.     

Regioselective Cleavage of Unstrained C?C Bond and C?H Bond: Palladium–Copper Catalyzed Deacetophenonylative Arylation of Coumarin Derivatives

A C_α C_β bond activation of the carbonyl group in unstrained ketones catalyzed cooperatively by palladium and copper(II) with the departure of the acetophenone has been developed, and the subsequent coupling with a variety of aromatics via the formal C H activation similar to the Friedel–Crafts reaction affords the skeleton‐reconstructed coumarin derivatives with high regioselectivity.     

Photo‐Induced Sonogashira C?C Coupling Reaction Catalyzed by Simple Copper(I) Chloride Salt at Room Temperature

The conventional thermal Sonogashira C C coupling reaction requires the use of a palladium catalyst and a large amount of ligands. Although there were a few reports describing the use of inexpensive metal catalysts, such as, copper (Cu), iron (Fe), and nickel (Ni), for replacement of palladium (Pd) in the Sonogashira reactions, it was later questioned that the observed effects were due to ppb levels contamination of Pd present in the reagents used in the reactions. Herein, we report that simple copper(I) chloride (CuCl) salt, in the absence of Pd and ligands, can catalyze the Sonogashira reaction with high yields (80–99%) under blue LED light irradiation at room temperature. Control experiments show that no cross‐coupling product was formed, when palladium(II) chloride (PdCl₂) was used to replace CuCl as a catalyst. A series of electron‐rich and electron‐poor substituted aryl halides (bromides and iodides) as well as aryl‐ and alkylacetylenes are examined and the reaction mechanism is discussed.     

Palladium‐Catalyzed Oxidative Annulation via C?H/N?H Functionalization: Access to Substituted Pyrroles

Pyrroles, ubiquitous bioactive heterocycles in nature, are readily prepared via a palladium‐catalyzed oxidative annulation of cyclic trans‐enamines to various internal alkynes in the absence of a directing group.

     

Palladium‐Catalyzed Oxidative C?H Bond Acylation of Acetanilides with Benzylic Alcohols

An efficient and clean method to construct C C bonds has been developed via the acylation reaction of acetanilides with benzylic alcohols using tert‐butyl hydroperoxide (TBHP) as oxidant catalyzed by palladium acetate in the presence of triflic acid (TfOH). The acylation reactions exhibit excellent reactivities, and up to 95% yield of the corresponding aryl ketone could be obtained under the optimal conditions.     

Building Functionality through Sequential C?B and C?F Bond Formation

α′‐Fluoro β‐boryl ketones can be efficiently synthesised from a sequential organocatalytic β‐boration pathway and consecutive electrophilic fluorination reaction in an acidic medium. Alternatively, the regioisomers of α‐fluoro β‐boryl ketones can be diastereoselectively obtained from Cu(I)‐mediated β‐boration followed by in situ fluorination of the boron enolate. Enantioenriched mixtures of the major anti‐diastereomer of vicinal C B and C F bonds are found in the presence of the chiral ligand QuinoxP*.     

Copper‐Catalyzed Intermolecular Amination of Acidic Aryl C?H Bonds with Primary Aromatic Amines

A copper‐catalyzed intermolecular aerobic oxidative C H bond amination of various polyfluorobenzenes with an array of primary aromatic amines was achieved for the first time. The reactivity of the polyfluorobenzenes was observed to depend on the acidity of C H bonds. Under similar reaction conditions, the C H bond amination of azoles also occurred.     

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.     

An Efficient Synthesis of Polysubstituted Pyridines via C?H Oxidation and C?S Cleavage of Dimethyl Sulfoxide

An expedient cleavage of the C S bond of dimethyl sulfoxide (DMSO) has been developed for the preparation of substituted pyridines from ketones. In this transformation, the co‐product formic acid was formed from ammonium formate, which acted as an important catalyst for the reaction. Notably, this transformation exhibited a broad substrate scope towards a wide variety of different ketones to give the corresponding substituted pyridines in high yields. Mechanistic studies suggested that dimethyl sulfoxide delivered a methylene fragment, which was subsequently captured in situ to give a pyridine.

     

Copper(II) Acetate/Oxygen‐Mediated Nucleophilic Addition and Intramolecular C?H Activation/C?N or C?C Bond Formation: One‐Pot Synthesis of Benzimidazoles or Quinazolines

Diarylcarbodiimides or benzylphenylcarbodiimides are converted to 1,2‐disubstituted benzimidazoles or 1,2‐disustituted quinazolines via addition/intramolecular C H bond activation/C‐N or C C bond forming reaction using copper(II) acetate/oxygen [Cu(OAc)₂/O₂] as the oxidant at 100 °C in one‐pot cascade procedure.     

Iron‐Catalyzed C?C Bond Cleavage and C?N Bond Formation

A novel approach for C N bond formation was developed by iron‐catalyzed C C bond cleavage. Anilines and sulfonamides reacted smoothly with 2‐substituted 1,3‐diphenylpropane‐1,3‐diones to afford N‐alkylation products, in which the 1,3‐dicarbonyl group acts as a leaving group in the presence of an iron catalyst. The reversible C C bond cleavage plays a driving force to give the thermodynamically stable products. The method is complementary to the previous methods for C N bond formation.     

Arene C?H Bond Functionalization Coupling with Cyclization of Allenes

Under the catalysis of a rhodium(III) complex, the cyclization of 2,3‐allenols was most probably initiated with the C H bond functionalization of N‐methoxybenzamides using the tetramethylcyclopentadiene anion (C₅Me₄⁻) as ligand, affording differently substituted 2,5‐dihydrofuran derivatives. Highly efficient axial‐to‐central chirality transfer has been observed.