A simple catalytic oxidation system was developed for the selective aerobic oxidation of structurally diverse benzylic sp3 CH bonds of ethers and alkylarenes. The reactions were performed with Fe(NO3)3·9H2O as the catalyst, KPF6 as the additive and molecular oxygen as the terminal oxidant without any ligands. Under the optimal reaction conditions, a number of isochromans, xanthenes and thioxanthenes can be converted to their corresponding esters or ketones in good to excellent yields.Download high-res image (160KB)Download full-size image

A new transition-metal-free 9-azabicyclo[3.3.1]nonan-N-oxyl (ABNO) catalyzed aerobic oxidative synthesis of 2-substituted 4H-3,1-benzoxazines and quinazolines has been developed through cascade reaction of aldehydes with 2-aminobenzyl alcohols and 2-aminobenzylamines, respectively. Under the optimal reaction conditions, the two kinds of heterocycles were obtained in 72–97 % isolated yield.

A simple synthesis method of nitriles from corresponding aldehydes by electrochemical oxidation was developed with ammonium acetate as the nitrogen source and 4-acetamido- 2,2,6,6-tetramethylpiperidinyl-l-oxy (4-AcNH-TEMPO) as the catalyst. Cyclic voltammetry was performed to investigate the electrocatalytic activity of 4-AcNH-TEMPO for the conversion of benzaldehyde to benzonitrile. On the basis of in situ FTIR data and cyclic voltammetry experiments, a reaction mechanism, involving the redox of 4-AcNH-TEMPO and the generation of intermediate imine during the reaction, was proposed. This electrocatalytic reaction system provided an efficient protocol for synthesis of aromatic nitriles at room temperature with moderate to high yields.

A simple and efficient method for the direct synthesis of nitriles from aldehydes using ammonium acetate as the nitrogen source has been developed. The reactions were performed with iodine as the catalyst and tert-butyl hydroperoxide (TBHP) as the oxidant under mild conditions. A variety of aromatic, heteroaromatic, aliphatic and allylic aldehydes could be converted into their corresponding nitriles in good to excellent yields.

•A novel electrochemical route to generate nitriles from aldehydes under mild conditions using a catalytic amount of TEMPO as the mediator and hexamethyldisilazane as the nitrogen source in the presence of acetic acid has been developed.•A plausible reaction mechanism is proposed based on the cyclic voltammetry, in situ FTIR and the confirmed intermediates.A novel electrochemical route to generate nitriles from aldehydes under mild conditions using a catalytic amount of TEMPO (2,2,6,6-tetramethylpiperidinyl-l-oxy) as the mediator and hexamethyldisilazane as the nitrogen source in the presence of acetic acid has been developed. A variety of aromatic, heteroaromatic and aliphatic aldehydes have been converted to their corresponding nitriles in good to excellent yields. A plausible reaction mechanism is proposed based on the cyclic voltammetry, in situ FTIR and the identification of intermediates.

A new biomimetic catalytic oxidation system which employs 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) as the catalyst, molecular oxygen as the terminal oxidant and iron(II) phthalocyanine (FeIIPc) as the electron-transfer mediator has been developed. This system can be applied for oxidative deprotection of PMB ethers, alcohol oxidation, aromatization and α,β-unsaturated aldehyde formation. After immobilizing FeIIPc on multi-walled carbon nanotubes, it can be reused without loss of activity.

•Synthesis of 3-sulfenylindoles from indoles and thiols.•Iodine as the catalyst and DMSO as the oxidant.•A wide range of substrates can be used.•Good to excellent yields can be obtained.•Easy operation and metal-free reaction conditions.An iodine-catalyzed regioselective sulfenylation of indoles in the presence of DMSO has been presented. Various indoles can react with aryl thiols or alkyl thiols to afford their corresponding 3-sulfenylindoles in good to excellent yields. The notable features of this protocol include easy operation, metal-free reaction conditions, and excellent functional group tolerance.An iodine-catalyzed regioselective sulfenylation of indoles in the presence of DMSO has been presented. Various indoles can react with aryl thiols or alkyl thiols to afford their corresponding 3-sulfenylindoles in good to excellent yields. The notable features of this protocol include easy operation, metal-free reaction conditions, and excellent functional group tolerance.

An efficient and convenient tert-butyl nitrite-catalyzed selective aerobic oxidation of thiols has been developed. Under the optimal reaction conditions, a number of thiol derivatives including aromatic thiols, heteroaromatic thiols and aliphatic thiols can be converted into their corresponding disulfides in good to excellent yields.An efficient and convenient tert-butyl nitrite-catalyzed selective aerobic oxidation of thiols has been developed. Various thiol derivatives can be converted into their corresponding disulfides in good to excellent yields.

A facile and efficient protocol for direct transformation of p-methoxybenzyl (PMB) ethers to aldehydes or ketones via a catalytic aerobic oxidation process has been developed. The reaction was performed with the combination of catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,2,6,6-tetramethylpiperidine N-oxy (TEMPO), and tert-butyl nitrite (TBN), with molecular oxygen as terminal oxidant. A variety of PMB ether substrates derived from benzylic alcohols, heteroaromatic alcohols, and aliphatic alcohols, were converted to their corresponding carbonyl compounds in good conversions and selectivities.A facile and efficient protocol for direct transformation of p-methoxybenzyl (PMB) ethers to aldehydes or ketones via a catalytic aerobic oxidation process has been developed. The reaction was performed with the combination of catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), 2,2,6,6-tetramethylpiperidine N-oxy (TEMPO), and tert-butyl nitrite (TBN), with molecular oxygen as terminal oxidant. A variety of PMB ether substrates derived from benzylic alcohols, heteroaromatic alcohols, and aliphatic alcohols, were converted to their corresponding carbonyl compounds in good conversions and selectivities.

An efficient 2,3-dichloro-5,6-dicyano-1,4-benzoquinone/tert-butyl nitrite-catalyzed aerobic oxidation of diarylmethane sp3 C–H bonds in the presence of acetic acid has been developed. Under the optimal reaction conditions, a number of diarylmethanes can be directly converted to their corresponding diarylketones in good to excellent yields. In addition, a plausible reaction mechanism has been investigated.An efficient 2,3-dichloro-5,6-dicyano-1,4-benzoquinone/tert-butyl nitrite-catalyzed aerobic oxidation of diarylmethane sp3 C–H bonds in the presence of acetic acid has been developed. Under the optimal reaction conditions, a number of diarylmethanes can be directly converted to their corresponding diarylketones in good to excellent yields. In addition, a plausible reaction mechanism has been investigated.

The derivative monomer of pyrrole with the side chain nitroxyl radical, 4-(3-(pyrrol-1-yl)propionamido)-2,2,6,6-tetramethylpiperidin-1-yloxy (PyATEMPO) was synthesized. Its corresponding polymer PPyATEMPO was successfully prepared by cyclic voltammetry on Pt electrode in NaClO4/CH3CN solution. The PPyATEMPO electrode showed high electrocatalytic activity for oxidation of benzyl alcohol in the presence of the Lewis base 2,6-lutidine. To further investigation, in situ Fourier transform infrared (FTIR) spectroscopy technique was applied to study the possible electrochemical oxidation mechanism of benzyl alcohol on PPyATEMPO electrode. It showed that the benzyl alcohol was selectively oxidized to benzaldehyde in the action of PPyATEMPO film.

A facile and efficient protocol for the oxidative deprotection of benzyl-type ethers has been developed. The reaction was performed with catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tert-butyl nitrite (TBN) under atmospheric pressure of O2. Under the optimal reaction conditions, a variety of p-methoxybenzyl (PMB), p-phenylbenzyl (PPB), and benzyl (Bn) ethers can be deprotected to their corresponding alcohols in excellent conversions and selectivities.A facile and efficient protocol for the oxidative deprotection of benzyl-type ethers has been developed. The reaction was performed with catalytic amounts of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) and tert-butyl nitrite (TBN) under atmospheric pressure of O2. Under the optimal reaction conditions, a variety of PMB, PPB, and Bn ethers can be deprotected to their corresponding alcohols in excellent conversions and selectivities.

The chemoselectivity in the amination of 4-chloroquinazolines with 3-amino-1H-pyrazoles was studied. Under the conditions of Pd2(dba)3/Xantphos/Na2CO3, 4-chloroquinazolines underwent selective amination with the cyclic secondary amino group of 3-amino-1H-pyrazoles, whereas 4-chloroquinazolines were exclusively aminated with the primary amino group of 3-amino-1H-pyrazoles via SNAr substitution in the presence of HCl.

A facile synthesis of aryl methyl ethers from phenols and dimethyl carbonate has been achieved in the presence of 1-n-butyl-3-methylimidazolium chloride ([BMIm]Cl). The reaction is carried out at 120 °C under atmospheric pressure. Aryl methyl ethers are obtained with excellent yields (>99%) at 100% selectivity for O-methylation. Moreover, [BMIm]Cl can be easily reused without loss of activity.