Using O2 as the oxidant, the benzoxazole frameworks can be directly constructed from the readily available phenols and primary amines in the presence of NH4PF6 over copper under mild conditions. Mechanistic studies showed that a novel mechanism involving biphenyldiols and o-quinones very possibly takes effect in the reaction, because both can selectively give the benzoxazoles under the reaction conditions. An unprecedented unstrained Caryl–Caryl bond cleavage takes place in the reaction.

A palladium-catalyzed Sonogashira-type coupling between arylsulfonyl hydrazides and terminal alkynes via Ar(C)–S bond cleavage is disclosed, which enables the general synthesis of functionalized internal alkynes, especially the Br-substituted ones, in good to excellent yields under acid- and base-free conditions.

Mn-Catalyzed oxidative amination of benzylic C(sp3)–H bonds with nitriles is disclosed, which enables the synthesis of a broad range of secondary amides in moderate to excellent yields under mild conditions. The interaction between Mn(III) and DDQ facilitates the oxidation and makes it highly efficient and selective.

A metal-free oxidative arene/alkene annulation-aromatization has been realized, which enables efficient synthesis of 2-arylnaphtho[2,1-b]furans from readily available terminal aryl alkenes and 2-naphthols. Mechanistic study suggests that this reaction proceeds via free-radical initiated tandem cyclization, dehydrogenative rearomatization and aromatization.A metal-free oxidative arene/alkene annulation-aromatization has been realized, which enables efficient synthesis of 2-arylnaphtho[2,1-b]furans from readily available terminal aryl alkenes and 2-naphthols. Mechanistic study suggests that this reaction proceeds via tandem cyclization, dehydrogenative rearomatization and aromatization.Download high-res image (145KB)Download full-size image

•A highly convenient synthesis for 3-substituted isocoumarins under mild conditions.•2-Bromobenzoic esters show higher efficiency and regioselectivity than those of 2-bromobenzoic acids.An efficient method for the synthesis of 3-substituted isocoumarins that are an important class of biologically active scaffolds via annulation of 2-bromobenzoic esters with terminal alkynes by copper catalyzed is described. The advantages of this method include mild reaction conditions, high yield and regioselectivity, and wide tolerance toward functional groups.Download high-res image (136KB)Download full-size image

A Cu-catalyzed selective aerobic heterocoupling of terminal alkynes is disclosed, which enables the synthesis of a broad range of unsymmetrical 1,3-diynes in good to excellent yields. The results disprove the long-held belief that homocouplings are exclusively favored in the Glaser–Hay reaction.

For the first time, the selective oxidative transformation of 2-naphthols with terminal alkynes is disclosed, which enables the straightforward synthesis of 2-arylnaphtho[2,1-b]furans in satisfactory yields under metal-free conditions. Mechanistic study suggests that the reaction proceeds via free-radical-mediated sp2-C–H bond activation, C–C coupling, and C–O cyclization.

Iron-catalyzed aerobic oxidative functionalization of sp3 C–H bonds has been developed for the construction of N-heterocycles from easily available carboxylic acid derivatives and o-substituted anilines. This transformation represents a widely applicable protocol to N-heterocycles using biofriendly iron as a catalyst in combination with molecular oxygen or air as the sole oxidant.

A nitrogen atom transfer to organic molecules via Cu-mediated C–N triple bond cleavage is firstly developed, which provides a variety of functionalized aryl nitriles from the readily accessible acetonitrile and aryl aldehydes.

An efficient synthesis of 2-hetarylquinazolin-4(3H)-ones via copper-catalyzed direct aerobic oxidative amination of sp3C–H bonds has been developed. This tandem oxidation–amination–cyclization transformation represents a straightforward protocol to prepare 2-hetaryl-substituted quinazolinones from easily available 2-aminobenzamides and (2-azaaryl)methanes.

A simple, efficient and highly functional group compatible method for the synthesis of propargylamines from terminal alkynes, dichloromethane and tertiary amines using silver catalysts has been developed.

An efficient metal-free aerobic oxidative C–N bond cleavage of tertiary amines has been developed to construct N-heterocycles using molecular oxygen as the sole oxidant with high atom efficiency, in which all of the three alkyl groups in tertiary amines can be utilized and transformed into N-heterocycles.

•A rapid ligand exchange takes place by treating [(R2P)2O(CuOAc)2]2 with aqueous NH4Cl to generate [(R2P)2O(CuCl)2]2 in good yields.•The geometry of [(R2P)2O(CuCl)2]2 varies with the R group of the phosphorus units.•Whereas [(R2P)2O(CuOAc)2]2 is air sensitive, [(R2P)2O(CuCl)2]2 is stable under air.The reaction of secondary phosphine oxides R2P(O)H 1 with Cu(OAc)2 under nitrogen atmosphere produced complexes [(R2P)2O(CuOAc)2]22. A rapid ligand exchange took place when treating complexes 2 with NH4Cl to generate [(R2P)2O(CuCl)2]23 in good yields. The structures of 3 were determined by X-ray crystallography, showing that the geometries of these tetranuclear copper complexes vary with the R group of the phosphorus units. Compared to complexes 2 which are air sensitive, complexes 3 are stable under air.The reaction of secondary phosphine oxides R2P(O)H 1 with Cu(OAc)2 under nitrogen atmosphere produced complexes [(R2P)2O(CuOAc)2]22. A rapid ligand exchange took place when treating complexes 2 with NH4Cl to generate [(R2P)2O(CuCl)2]23 in good yields. The structures of 3 were determined by X-ray crystallography, showing that the geometries of these tetranuclear copper complexes vary with the R group of the phosphorus units. Compared to complexes 2 which are air sensitive, complexes 3 are stable under air.

A metal-free regioselective hydrobromination of alkynes has been developed to provide the Markovnikov-type vinyl bromides in good yields using dibromomethane/N,N-dimethylaniline as in-situ ‘HBr’ source. This protocol also represents an elegant example of the activation of sp2 CH and CBr bonds in one pot, in which ‘HBr’ is generated and transferred under mild metal-free conditions. D-incorporated experiments were employed to investigate the reaction mechanism and a plausible reaction path was proposed.A metal-free regioselective hydrobromination of alkynes has been developed to provide the Markovnikov-type vinyl bromides in good yields using dibromomethane/N,N-dimethylaniline as in-situ ‘HBr’ source. This protocol also represents an elegant example of the activation of sp2 CH and CBr bonds in one pot, in which ‘HBr’ is generated and transferred under mild metal-free conditions. D-incorporated experiments were employed to investigate the reaction mechanism and a plausible reaction path was proposed.

Mn-Catalyzed oxidative amination of benzylic C(sp3)–H bonds with nitriles is disclosed, which enables the synthesis of a broad range of secondary amides in moderate to excellent yields under mild conditions. The interaction between Mn(III) and DDQ facilitates the oxidation and makes it highly efficient and selective.

Iron-catalyzed aerobic oxidative functionalization of sp3 C–H bonds has been developed for the construction of N-heterocycles from easily available carboxylic acid derivatives and o-substituted anilines. This transformation represents a widely applicable protocol to N-heterocycles using biofriendly iron as a catalyst in combination with molecular oxygen or air as the sole oxidant.

A nitrogen atom transfer to organic molecules via Cu-mediated C–N triple bond cleavage is firstly developed, which provides a variety of functionalized aryl nitriles from the readily accessible acetonitrile and aryl aldehydes.

A simple, efficient and highly functional group compatible method for the synthesis of propargylamines from terminal alkynes, dichloromethane and tertiary amines using silver catalysts has been developed.

An efficient metal-free aerobic oxidative C–N bond cleavage of tertiary amines has been developed to construct N-heterocycles using molecular oxygen as the sole oxidant with high atom efficiency, in which all of the three alkyl groups in tertiary amines can be utilized and transformed into N-heterocycles.