Iron(III) Complexes with Pyridine Group Coordination and Dissociation Reversible Equilibrium: Cooperative Activation of CO2 and Epoxides into Cyclic Carbonates.

Herein, a series of [ONSN]-type iron(III) complexes were synthesized. A binary catalytic system in combination with iron complexes and tetrabutylammonium bromide (TBAB) exhibited high activity for the synthesis of cyclic carbonates from CO2 (1 atm) and terminal epoxides at room temperature. Additionally, single-component iron complexes without using additional TBAB as nucleophiles also showed high activity for the cycloaddition of CO2 and terminal epoxides under 80 °C and 0.5 MPa of CO2. This study demonstrates that single-component iron catalysts provide a competitive alternative to binary catalytic systems for the synthesis of cyclic carbonates from CO2 and epoxides. Mechanistic studies on a single-component iron catalytic system suggest that the temperature serves as a role of responsive switch for controlling the coordination and dissociation of pyridine bearing iron catalysts detected using in situ infrared spectroscopy, and uncoordinated pyridine activates CO2 to form carbamate. Studies of electrospray ionization high-resolution mass spectrometry reveal that an iron center was used as a Lewis acidic site, free halogen anions from the iron center were used as a nucleophilic site, and coordinated pyridine was released from iron complexes to activate CO2.

Selective Oxidative Methyl C-H Functionalization of Butylated Hydroxytoluene toward Arylimines/N-Heterocycles.

A metal-free and selective oxidative methyl C-H functionalization of BHT with aniline compounds has been developed. This innovative method enables the facile and efficient synthesis of a diverse array of BHT-functionalized N-containing skeletons, including arylamines, benzoxazoles, benzothiazoles, benzimidazoles, quinazolines, and quinazolinones, all of which are challenging to access. The control experiment involving TEMP18O suggests that the radical adduct of TEMPO with the benzyl radical of BHT may serve as an intermediate.

Ni-catalyzed C-F activation to construct C-P bond with P-P(O) and P(O)OR mediation.

Here we developed an efficient Ni-catalyzed C-F bond phosphorylation of aryl fluorides via the crucial intermediates of P-P(O) and P(O)OR. P-P(O) mediated organophosphorus generation is observed for active aryl fluorides, whereas inactive aryl fluorides can also be activated and phosphorylated via a P(O)OR-mediated pathway, which is barely reported yet. Facile scale-up to the gram level and the upgrading of the bioactive molecule make this protocol to have promising applications in synthetic chemistry.

Metal-Free Oxidative Annulation of Phenols and Amines: A General Synthesis of Benzoxazoles.

The ubiquity of benzoxazoles in natural products, drugs, and functional materials has stimulated numerous efforts toward their synthesis; however, the developed methods rely on prefunctionalized substrates and lack generality. Under metal-free conditions, a highly general synthesis of benzoxazoles direct from abundant and easily available phenols and amines is developed via a modular phenol functionalization controlled by TEMPO. In the reaction, various phenols and primary amines with a broad range of functional groups are compatible, producing structurally and functionally diverse benzoxazoles (64 examples) without or with trace observation of the byproducts of phenol transformation with amines. The practical synthesis, especially for drug tafamidis, demonstrates decisive advantages in generality, selectivity, efficiency, and atom- and step-economies over traditional methods, even in the cases of low yields. Mechanistically, the radical adducts of TEMPO with ortho-cyclohexa-2,4-dien-1-one radicals rather than the well-recognized cyclohexa-3,5-diene-1,2-diones may serve as intermediates.

TEMPO mediated oxidative annulation of aryl methyl ketones with amines/ammonium acetate for imidazole synthesis.

A facile synthesis of 1H-imidazoles by direct oxidative annulation of aryl methyl ketones and primary amines has been developed in the presence of TEMPO under weakly acidic conditions. By replacing amines with ammonium acetate, 2H-imidazole skeletons were achieved for the first time from ketones. Substrates containing various functional groups, such as alkyl, aryl, naphthyl, halogen (F, Cl, Br, I), nitro, trifluoromethyl, sulfonyl ester, furyl, thienyl, and pyridyl groups, were readily transformed into the desired products. The application potential of this method was verified by the scale-up synthesis and Sonogashira coupling functionalization of imidazoles. Mechanistically, the α-TEMPO-enamine adduct may serve as the key reaction intermediate.

Cu-Catalyzed Oxidative Thioesterification of Aroylhydrazides with Disulfides.

An alternative thioesterification reaction via copper-catalyzed oxidative coupling of readily available aroylhydrazides with disulfides is developed, in which oxidative expulsion of N2 overcomes the activation barrier between the carboxylic acid derivatives and the products. The reaction produces various thioesters in good to excellent yields with good functional group tolerance. In the reaction, stable and easily available aroylhydrazides are used as acyl sources and the relatively odorless disulfides are used as S sources. Mechanistic investigations demonstrate that the reaction of copper salt and oxidant (NH4)2S2O8 allows for achievement of tandem processes, including deprotonation, free-radical-mediated denitrogenation, and C-S bond formation.

Phosphorous Acid-Catalyzed Alkylation of Phenols with Alkenes.

A H3PO3-catalyzed alkylation of phenols with alkenes is achieved in a facile, efficient, and selective manner. The reaction shows a unique selectivity, i.e., excellent regioselectivity, thorough suppression of overalkylation, without alkylation of a simple phenyl ring, and can selectively provide ortho-, meta-, or para-alkylated phenol derivatives in good to excellent yields. This feature along with mild reaction conditions, sensitive functional group tolerance, and scale-up synthesis and late modification of phenolic bioactive compounds make it an ideal and practical alternative for the modification of phenols.

The palladium-catalyzed direct C3-cyanation of indoles using acetonitrile as the cyanide source.

The ligand-free palladium-catalyzed C3-cyanation of indoles via direct C-H functionalization was achieved. This protocol, utilizing CH3CN as a green and readily available cyanide source, produced the desired products in moderate to good yields through transition-metal-catalyzed C-CN bond cleavage.

Cu(I)-Catalyzed 6- endo-dig Cyclization of Terminal Alkynes, 2-Bromoaryl Ketones, and Amides toward 1-Naphthylamines: Applications and Photophysical Properties.

Functional group substituted 1-naphthylamines, especially N-methylated ones, play important roles in numerous chemical and biological processes. However, these compounds' general and step-economic syntheses are highly limited, which seriously restricts efforts to improve the properties and develop new functions for this kind of compound. In this report, we describe the development of an efficient, convenient, and general method for the synthesis of valuable functionalized 1-naphthylamines directly from readily available terminal alkynes, 2-bromoaryl ketones, and amides via Cu(I)-catalyzed benzannulation in a green solvent (i.e., water) under Pd- and ligand-free conditions. A total of 82 functionalized 1-naphthylamines, especially synthetically and biologically useful N-methylated compounds, are synthesized in isolated yields up to 95%. Some unique features of the reaction are as follows: (1) exclusive 6 -endo-dig selectivity, (2) ready incorporation of a broad range of functional groups directly from easily available substrates, and (3) amides that can be used as aminating agents and that are excellent alternatives to toxic and/or odorous amines. Due to facile tuning of functional groups for the reaction, the products possess good electronic donor-acceptor structures and exhibit intriguing photophysical properties, such as tunable and polarity-sensitive fluorescence emission and large Stokes shifts (up to 258 nm). Utilizing the products' unique polarity-sensitive fluorescence response, we successfully applied the 1-naphthylamine derivatives, such as compound 91, to image lipid droplets (LDs) and monitor cellular LDs growth. The previously mentioned advantages of this methodology, along with the mild conditions, simple operation, and scalable synthesis, may allow this novel reaction to be extended to varied applications in chemistry, biology, and materials science.

Transition-Metal-Free C-P Bond Formation via Decarboxylative Phosphorylation of Cinnamic Acids with P(O)H Compounds.

A novel, transition-metal-free phosphorylation of cinnamic acids with P(O)H compounds has been developed via radical-promoted decarboxylation under mild conditions. This method provides simple, efficient, and versatile access to valuable ( E)-alkenylphosphine oxides in satisfactory yields with a wide variety of substrates.

Palladium-Catalyzed Desulfitative Cross-Coupling of Arylsulfonyl Hydrazides with Terminal Alkynes: A General Approach toward Functionalized Internal Alkynes.

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.

Manganese(iii) acetate catalyzed oxidative amination of benzylic C(sp3)-H bonds with nitriles.

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.

Copper Catalysis for Selective Heterocoupling of Terminal Alkynes.

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.

Metal- and Oxidant-Free Synthesis of Quinazolinones from ß-Ketoesters with o-Aminobenzamides via Phosphorous Acid-Catalyzed Cyclocondensation and Selective C-C Bond Cleavage.

A general and efficient phosphorous acid-catalyzed cyclocondensation of ß-ketoesters with o-aminobenzamides via selective C-C bond cleavage leading to quinazolinones is developed. This reaction proceeds smoothly under metal- and oxidant-free conditions, giving both 2-alkyl- and 2-aryl-substituted quinazolinones in excellent yields. This strategy can also be applied to the synthesis of other N-heterocycles, such as benzimidazoles and benzothiazoles.

Catalyst-Free and Selective C-N Bond Functionalization: Stereospecific Three-Component Coupling of Amines, Dichloromethane, and >P(O)H Species Affording α-Aminophosphorus Compounds.

Catalyst-free and selective C-N bond functionalization has been achieved through three-component coupling of amines, dihalomethane, and >P(O)H species. This reaction takes place stereospecifically with retention of configuration at phosphorus, which can produce various new optically active phosphorus analogues of α-amino acids.

Cu-mediated nitrogen atom transfer via C≡N bond cleavage.

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.

Copper catalysed direct amidation of methyl groups with N-H bonds.

An efficient copper catalyzed direct aerobic oxidative amidation of methyl groups of azaarylmethanes with N-H bonds producing amides is successfully developed, which can produce primary, secondary and tertiary amides, including those with functional groups. This reaction represents a straightforward method for the preparation of amides from the readily available hydrocarbon starting materials.

Copper-catalyzed aerobic oxidative inert C-C and C-N bond cleavage: a new strategy for the synthesis of tertiary amides.

A copper-catalyzed aerobic oxidative amidation reaction of inert C-C bonds with tertiary amines has been developed for the synthesis of tertiary amides, which are significant units in many natural products, pharmaceuticals, and fine chemicals. This method combines C-C bond activation, C-N bond cleavage, and C-H bond oxygenation in a one-pot protocol, using molecular oxygen as the sole oxidant without any additional ligands.

Metal-free aerobic oxidative C-N bond cleavage of tertiary amines for the synthesis of N-heterocycles with high atom efficiency.

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.

Efficient synthesis of propargylamines from terminal alkynes, dichloromethane and tertiary amines over silver catalysts.

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.