KOtBu-promoted oxidative dimerizations of 2-methylquinolines to 2-alkenyl bisquinolines with molecular oxygen

KO^tBu-promoted oxidative dimerizations of 2-methylquinolines with molecular oxygen as the oxidant have been developed for the first time. The mild reaction conditions allow the homo- and cross-dimerizations of 2-methylquinolines to give functionalized 2-alkenyl bisquinolines in highly trans-selective manners.

KO^tBu-promoted oxidative dimerizations of 2-methylquinolines with molecular oxygen as the oxidant have been developed for the first time.     

Efficient and sustainable laccase-catalyzed iodination of p-substituted phenols using KI as iodine source and aerial O2 as oxidant

The laccase-catalyzed iodination of p-hydroxyarylcarbonyl- and p-hydroxyarylcarboxylic acid derivatives using KI as iodine source and aerial oxygen as the oxidant delivers the corresponding iodophenols in a highly efficient and sustainable manner with yields up to 93% on a preparative scale under mild reaction conditions.

A new and sustainable laccase-catalyzed iodination of p-substituted phenols using KI as iodine source and aerial O₂ as oxidant has been developed.     

Access to indolines from primary phenylethylamines by an unexpected palladium-catalyzed C–H functionalization process

A new method for the preparation of 2,2-disubstituted indolines from 2-phenylethylamines was developed under Pd catalysis and PhI(OAc)₂ as oxidant. Imines derived from 2-pyridinecarboxaldehyde were formed in situ to direct a C–H activation process. The resulting imines were also oxidized to the corresponding amides in the same Pd-catalyzed process to obtain the final indoline as a picolinamide.

A new method for the preparation of 2,2-disubstituted indolines from 2-phenylethylamines was developed under Pd catalysis and PhI(OAc)₂ as oxidant.     

Metal-free oxidative coupling of arylmethylamines with indoles: a simple,environmentally benign approach for the synthesis of 3,3′-bis(indolyl)methanes

The efficient metal-free oxidative coupling of arylmethylamines with indoles has been developed using molecular oxygen as a green oxidant. The present reaction provides a novel route towards the synthesis of 3,3′-bis(indolyl)methanes in excellent yields of up to 95% via C–C and C–N bond formation. This attractive and environmentally friendly one-pot protocol is a simple procedure that features inexpensive acetic acid as the catalyst and molecular oxygen as the sole oxidant, and it supports a wide substrate scope with the good tolerance of functional groups.

The efficient metal-free oxidative coupling of arylmethylamines with indoles has been developed using molecular oxygen as a green oxidant towards a novel rout of 3,3′-bis(indolyl)methanes (BIMs) synthesis.     

An efficient one-pot conversion of carboxylic acids into benzimidazoles via an HBTU-promoted methodology

Benzimidazole is a privileged, and routinely used pharmacophore in the drug discovery process. Herein, we report a mild, acid-free and one-pot synthesis of indole, alkyl and alpha-amino benzimidazoles through a novel HBTU-promoted methodology. An extensive library of indole-carboxylic acids, alkyl carboxylic acids and N-protected alpha-amino acids has been converted into the corresponding benzimidazoles in 80–99% yield. Since alpha-aminobenzimidazoles are highly useful synthons as chiral ligands for chemical catalysis, as well as for drug discovery endeavors, our reported method provides direct access to this scaffold in a simple, one-pot operation from commercially available carboxylic acids.

A mild, one-pot and HBTU-promoted method for the synthesis of structurally diverse benzimidazoles is reported, exhibiting a broad substrate scope.     

Cu(OAc)2 catalysed aerobic oxidation of aldehydes to nitriles under ligand-free conditions

An economically efficient and environmentally benign approach for the direct oxidative transformation of aldehydes to nitriles has been developed using commercially available non-toxic copper acetate as an inexpensive catalyst and ammonium acetate as the source of nitrogen in the presence of aerial oxygen as an eco-friendly oxidant under ligand-free conditions. The reactions were associated with high yield and various sensitive moieties like allyloxy, benzyloxy, t-butyldimethylsilyloxy, hetero-aryl, formyl, keto, chloro, bromo, methylenedioxy and cyano were well tolerated in the aforesaid method. The kinetic studies showed first order dependency on the aldehyde substrate in the reaction rate. The reaction was faster with the electron deficient aldehydes as confirmed by Hammett analysis. Moreover, the present oxidative method was effective on larger scales showing potential for industrial application.

An economically efficient ligand-free oxidative conversion of aldehydes to nitriles has been achieved using Cu(OAc)₂ and NH₄OAc as inexpensive materials of low toxicity in the presence of aerial oxygen as an eco-friendly oxidant.     

A copper(ii)-catalyzed annulative formylation of o-alkynylanilines with DMF: a single-step strategy for 3-formyl indoles

In this paper, a copper(ii)-catalyzed reaction of o-alkynylanilines with dimethylformamide (DMF) in the presence of oxygen has been developed for synthesizing multisubstituted 3-formyl indole scaffolds. This one-pot reaction proceeds through a cascade 5-endo-dig cyclization followed by formylation to construct 1,2-disubstituted 3-formyl indoles. The key aspects of this synthesis method are the broad substrate scope (with 38 examples), and well tolerating various functional groups. In addition, a detailed mechanism has been proposed, where DMF may serve as a carbon source for the in situ C3 formylation of the obtained indole derivatives.

In this paper, a copper(ii)-catalyzed reaction of o-alkynylanilines with dimethylformamide (DMF) in the presence of oxygen has been developed for synthesizing multisubstituted 3-formyl indole scaffolds.     

Catalyst- and solvent-free ipso-hydroxylation of arylboronic acids to phenols

A catalyst-free method for the hydroxylation of arylboronic acids to form the corresponding phenols with sodium perborate as the oxidant was developed using water as the solvent. Under the reaction conditions, the yield of phenol reached 92% at only 5 min. Moreover, the reaction could be conducted without a catalyst under the solvent-free condition, the efficiency of which was as high as that of a liquid-phase reaction. Using a microcalorimeter, the reaction was found to be an exothermic reaction. The reaction mechanism was investigated and understood via DFT calculations, which revealed that it was a nucleophilic reaction.

A catalyst-free method for the hydroxylation of arylboronic acids to form the corresponding phenols with sodium perborate as the oxidant was developed using water as the solvent or solvent free condition.     

Direct oxidation of N-ynylsulfonamides into N-sulfonyloxoacetamides with DMSO as a nucleophilic oxidant

N-Arylethynylsulfonamides are oxidized into N-sulfonyl-2-aryloxoacetamides directly and efficiently with dimethyl sulfoxide (DMSO) as both an oxidant and solvent with microwave assistance. DFT calculations indicate that DMSO nucleophilically attacks the ethylic triple bond and transfers its oxygen atom to the triple bond to form zwitterionic anionic N-sulfonyliminiums to trigger the reaction. Then it nucleophilically attacks the generated iminium intermediates to accomplish the oxidation via the second oxygen atom transfer. The current method provides a straightforward and efficient strategy to transform various N-arylethynylsulfonamides into N-sulfonyl-2-aryloxoacetamides, sulfonyl oxoacetimides, without any other electrophilic activators or oxidants.

Microwave-assisted direct oxidation of N-arylethynylsulfonamides with DMSO as a nucleophilic oxidant and solvent affords N-sulfonyl-2-aryloxoacetamides without any other additional electrophilic activators or oxidants.     

Nickel catalyzed intramolecular oxidative coupling: synthesis of 3-aryl benzofurans

Recent research has been focused on the transition metal-catalyzed reactions. Herein we have developed nickel-catalyzed synthesis of 3-aryl benzofurans from ortho-alkenyl phenols via intramolecular dehydrogenative coupling. Notably, simple O₂ gas served as an oxidant, without using any sacrificial hydrogen acceptor. The strategy enabled the synthesis of 3-aryl benzofurans in good to excellent yields.

We have developed nickel-catalyzed synthesis of 3-aryl benzofurans from ortho-alkenyl phenols via intramolecular dehydrogenative coupling. O₂ gas served as an oxidant and 3-aryl benzofurans were synthesized in good to very good yields.     

Practical scale up synthesis of carboxylic acids and their bioisosteres 5-substituted-1H-tetrazoles catalyzed by a graphene oxide-based solid acid carbocatalyst

Herein, catalytic application of a metal-free sulfonic acid functionalized reduced graphene oxide (SA-rGO) material is reported for the synthesis of both carboxylic acids and their bioisosteres, 5-substituted-1H-tetrazoles. SA-rGO as a catalytic material incorporates the intriguing properties of graphene oxide material with additional benefits of highly acidic sites due to sulfonic acid groups. The oxidation of aldehydes to carboxylic acids could be efficiently achieved using H₂O₂ as a green oxidant with high TOF values (9.06–9.89 h⁻¹). The 5-substituted-1H-tetrazoles could also be effectively synthesized with high TOF values (12.08–16.96 h⁻¹). The synthesis of 5-substituted-1H-tetrazoles was corroborated by single crystal X-ray analysis and computational calculations of the proposed reaction mechanism which correlated well with experimental findings. Both of the reactions could be performed efficiently at gram scale (10 g) using the SA-rGO catalyst. SA-rGO displays eminent reusability up to eight runs without significant decrease in its productivity. Thus, these features make SA-rGO riveting from an industrial perspective.

Scalable synthesis of carboxylic acids and their bioisosteres, 5-substituted-1H-tetrazoles, catalyzed by phenylsulfonic acid functionalized reduced graphene oxide.     

Visible light-mediated photocatalytic oxidative cleavage of activated alkynes via hydroamination: a direct approach to oxamates

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature. In this reaction, the single electron oxidation of an in situ formed enamine followed by radical coupling with an oxidant finally delivers the oxamate. The key features of this photocatalytic reaction are the mild reaction conditions, metal-free organic dye as a photocatalyst, and TBHP playing a dual role as “O” source and for the regeneration of the photocatalyst.

The direct oxidative cleavage of activated alkynes via hydroamination has been described using organic photocatalyst under visible-light irradiation at room temperature.     

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.

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.     

Copper-catalyzed in situ oxidative-coupling for one-pot synthesis of 5-aryl-1,4-disubstituted 1,2,3-triazoles under mild conditions

A new reaction system with CuCl as catalyst, TEA as base and O₂/chloramine-T as oxidant was developed for one-pot in situ oxidative-coupling to synthesize 5-aryl-1,4-disubstituted 1,2,3-triazoles in this paper. A variety of 5-arylated-1,2,3-triazole compounds could be efficiently prepared directly from the readily accessible organic azides, terminal alkynes and arylboronic acids. Advantages of the method include use of low-cost catalyst, clean oxidant, less-toxic additive, and low reaction temperature. Importantly, due to avoiding harsh strong basic reagents and high temperatures, the presented method can offer mild conditions for multi-component synthesis of 5-aryl-1,2,3-triazoles from the designed structurally complicated alkynyl or azide donors bearing natural product motifs and sensitive functional groups.

A new reaction system with CuCl as catalyst, TEA as base and O₂/chloramine-T as oxidant was developed for one-pot in situ oxidative-coupling to synthesize 5-aryl-1,4-disubstituted 1,2,3-triazoles in this paper.     

Chan–Lam coupling reaction of sulfamoyl azides with arylboronic acids for synthesis of unsymmetrical N-arylsulfamides

An efficient method was developed for the synthesis of unsymmetrical N-arylsulfamides using sulfamoyl azides and arylboronic acids in the presence of 10 mol% of copper chloride as the catalyst. The reaction was facilitated in MeOH in an open flask at room temperature. Unlike the coupling of sulfamides and boronic acids, the use of sulfamoyl azides was found to be beneficial with respect to the yield and reaction time.

An efficient method was developed for the synthesis of unsymmetrical N-arylsulfamides using sulfamoyl azides and arylboronic acids in the presence of 10 mol% of copper chloride as the catalyst.     

The synthesis of imidazo[1,5-a]quinolines via a decarboxylative cyclization under metal-free conditions

An iodine-mediated decarboxylative cyclization was developed from α-amino acids and 2-methyl quinolines under metal-free conditions, affording a variety of imidazo[1,5-a]quinolines with moderate to good yields.

An iodine-mediated decarboxylative cyclization was developed from α-amino acids and 2-methyl quinolines under metal-free conditions, affording a variety of imidazo[1,5-a]quinolines with moderate to good yields.     

Metal-free photoredox-catalyzed direct α-oxygenation of N,N-dibenzylanilines to imides under visible light

An efficient synthesis of imides using metal-free photoredox-catalyzed direct α-oxygenation of N,N′-disubstituted anilines in the presence of 9-mesityl-10-methylacridinium [Acr⁺-Mes]BF₄ as a photoredox catalyst and molecular oxygen as a green oxidant under visible light was developed. This photochemical approach offered operational simplicity, high atom economy with a low E-factor, and functional group tolerance under mild reaction conditions. Control and quenching experiments confirmed the occurrence of a radical pathway and superoxide radical anion α-oxygenation reactions, and also provided strong evidence for the reductive quenching of [Acr⁺-Mes]BF₄ based on a Stern–Volmer plot, which led to the proposed mechanism of this reaction.

A visible-light-mediated direct α-oxygenation of N,N-dibenzylanilines to imides in the presence of [Acr⁺-Mes]BF₄ as a metal-free photocatalyst and O₂ as a green oxidant.     

Iodine-catalyzed convergent aerobic dehydro-aromatization toward benzazoles and benzazines

An iodine-catalyzed aerobic dehydro-aromatization has been developed, providing straightforward and efficient access to various benzoazoles and benzoazines. The present transition-metal-free protocol enables the dehydro-aromatization of tetrahydrobenzazoles and tetrahydroquinolines with molecular oxygen as the green oxidant, along with some other N-heterocycles. Hence, a broad range of heteroaromatic compounds are generated in moderate to good yields under facile reaction conditions.

An iodine-catalyzed aerobic dehydro-aromatization has been developed, providing a straightforward and efficient access to various benzoazoles and benzoazines.     

Cerium photocatalyzed radical smiles rearrangement of 2-aryloxybenzoic acids

We report herein a cerium photocatalyzed aryl migration from an aryl ether to a carboxylic acid group through radical-Smiles rearrangement. This operationally simple protocol utilizes inexpensive CeCl₃ as a photocatalyst and converted a variety of 2-aryloxybenzoic acids into aryl-2-hydroxybenzoates in good yields.

Visible light-driven CeCl₃-mediated aryl migration from an aryl ether to a carboxylic acid group through radical-Smiles rearrangement is reported.     

A scalable and green one-minute synthesis of substituted phenols

A mild, green and highly efficient protocol was developed for the synthesis of substituted phenols via ipso-hydroxylation of arylboronic acids in ethanol. The method utilizes the combination of aqueous hydrogen peroxide as the oxidant and H₂O₂/HBr as the reagent under unprecedentedly simple and convenient conditions. A wide range of arylboronic acids were smoothly transformed into substituted phenols in very good to excellent yields without chromatographic purification. The reaction is scalable up to at least 5 grams at room temperature with one-minute reaction time and can be combined in a one-pot sequence with bromination and Pd-catalyzed cross-coupling to generate more diverse, highly substituted phenols.

The synthesis of highly substituted phenols is advanced via a green one minute hydroxylation and subsequent one-pot functionalizations.