Aerobic Oxidation of PMB Ethers to Carboxylic Acids

The first aerobic protocol of direct transformation of p-methoxybenzyl (PMB) ethers to carboxylic acids efficiently with Fe(NO3)3 ⋅ 9H2O and TEMPO as catalysts at room temperature has been developed. The reaction accommodates C-Br bond, terminal/non-terminal C-C triple bond, amide, cyano, nitro, ester, and trifluoromethyl groups. Even highly selective oxidative deprotection of different benzylic PMB ethers has been realized. The reaction has been successfully applied to the total synthesis of natural product, (R)-6-hydroxy-7,9-octadecadiynoic acid, demonstrating the practicality of the method. Based on experimental studies, a possible mechanism involving oxygen-stabilized benzylic cation has been proposed.

Iron-catalyzed aerobic oxidation of silyl ethers to carboxylic acids

Direct aerobic oxidation of silyl ethers to carboxylic acids has been developed. The mild reaction conditions lead to a broad range of functional group compatibility. Different types of silyl groups have been investigated and selective deprotective oxidation has been realized. The reaction could be conducted under air.

MOF-Zn-NHC as an efficient N-heterocyclic carbene catalyst for aerobic oxidation of aldehydes to their corresponding carboxylic acids via a cooperative geminal anomeric based oxidation

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation. Features such as mild reaction conditions and no need for a co-catalyst or oxidative reagent can be considered as the major advantages of the presented method in this study.

As an efficient heterogenous N-heterocyclic carbene (NHC) catalyst, MOF-Zn-NHC was used in the aerobic oxidation of aryl aldehydes to their corresponding carbocyclic acids via an anomeric based oxidation.

Transfer of metals in the liquids of electronic cigarettes

Objectives: E-cigarettes are electronic devices containing a liquid that usually consists of a mixture of glycerol, propylene glycol and nicotine, with or without flavorings, in various concentrations. A vapor or aerosol is produced, and inhaled from the user, when this liquid is heated by a heating coil. This work examines the impact of three parameters (e-liquid composition, nicotine content and air flow) on the transfer of metals' from the heating coils to the e-liquids.Materials and methods: A distillation unit was used, where 20ml of an e-liquid were boiled with two commercial heating elements. Four e-liquids: 100% Propylene Glycol, 100% Glycerol, 50/50% Propylene Glycol/Glycerol, 33.3/33.3/33.3% Propylene Glycol/Glycerol/Water, three nicotine contents: 0, 0.4 and 0.8% per volume and three air flows: 0, 0.5 and 1.0 L/min, were used. The liquids were analyzed by Total Reflection X-Ray Fluorescence spectrometry to determine the final content of metals.Results and discussion: Five metals, Fe, Ni, Cu, Zn, and Pb, were found to be transferred from the heating coils to the e-liquids. The transfer of those metals increases with air flow and nicotine concentration, while e-liquid composition also has a significant impact. Glycerol enhances the transfer of metals compared to propylene glycol and their mixtures. The boiling temperature of the e-liquids increases significantly the transfer of metals in the e-liquids.Conclusions: There is a transfer of metals from the heating coils to the e-liquids. This transfer depends on the e-liquid composition and on the boiling temperature.

Reinvestigation of the Organocatalyzed Aerobic Oxidation of Aldehydes to Acids

The organocatalyzed aerobic oxidation of aldehydes to acids was reproduced from the original report. In- and ex-situ analysis of the reaction mixture as the function of time reveals that, unlike the claim in the publication, the aerobic oxidation of aromatic and aliphatic aldehydes leads predominantly to the formation of peracids. The latter are transformed into the corresponding carboxylic acids during the workup procedure. The buildup of peracids in solution poses safety problems that should not be overlooked. This finding has also an influence on the way new catalysts are investigated to improve this reaction as well as on aerobic aldehyde-mediated co-oxidation.

Cu-catalyzed oxygenation of alkene-tethered amides with O2 via unactivated C[double bond, length as m-dash]C bond cleavage: a direct approach to cyclic imides

An efficient aerobic unactivated C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond cleavage process was achieved, in which the succinimide or glutarimide derivatives could be prepared directly from alkenyl amides.

The transformations of unactivated alkenes through C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond double cleavage are always attractive but very challenging. We report herein a chemoselective approach to valuable cyclic imides by a novel Cu-catalyzed geminal amino-oxygenation of unactivated C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bonds. O₂ was successfully employed as the oxidant as well as the O-source and was incorporated into alkenyl amides via C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C bond cleavage for the efficient preparation of succinimide or glutarimide derivatives. Moreover, the present strategy under simple conditions can be used in the late-stage modification of biologically active compounds and the synthesis of pharmaceuticals, which demonstrated the potential application.

Efficient Syntheses of Traumatic Lactone and Rhizobialide

Herein, we report the total synthesis of traumatic lactone and rhizobialide by utilizing allenoic acid to construct the lactone ring. The key starting materials, allenoic acids, could be prepared by the ATA (allenation of terminal alkynes) of a terminal alkyne with an aldehyde that contained a protected hydroxyl group followed by hydrolysis. Importantly, the asymmetric synthesis could be realized just by replacing racemic diphenylprinol with (R)- or (S)-diphenylprinol to deliver the optically active allenoate.

Catalytic enantioselective construction of axial chirality in 1,3-disubstituted allenes

Metal-catalyzed enantioselective construction of the loosening axial allene chirality spreading over three carbon atoms using a chiral ligand is still a significant challenge. In the literature, steric effect of the substrates is the major strategy applied for such a purpose. Herein, we present a general palladium-catalyzed asymmetrization of readily available racemic 2,3-allenylic carbonates with different types of non-substituted and 2-substituted malonates using (R)-(−)-DTBM-SEGPHOS as the preferred ligand to afford 1,3-disubstituted chiral allenes with 90~96% ee. This protocol has been applied to the first enantioselective synthesis of natural product, (R)-traumatic lactone. Control experiments showed that in addition to the chiral ligand, conducting this transformation via Procedure C, which excludes the extensive prior coordination of the allene unit in the starting allene with Pd forming a species without the influence of the chiral ligand, is crucial for the observed high enantioselectivity.

Highly enantioselective synthesis of allenes has been relying, so far, on the steric hindrance of substrates. Here the authors achieve excellent stereocontrol in the synthesis of chiral allenes with a palladium-DTBM-SEGPHOS catalytic system in a non-substrate-dependent manner.

Transition-metal free selective C(α)–C(β) bond cleavage of trifluoromethyl ketones with amidines under air: facile access to 5-trifluoromethylated Imidazol-4-ones

Synthesis of 5-trifluoromethylated imidazol-4-ones via transition-metal-free selective C(α)–C(β) bond cleavage of trifluoromethyl ketones with amidines under air.

Copper catalysis for highly selective aerobic oxidation of alcohols to aldehydes/ketones

A general and practical room temperature aerobic oxidation of different types of alcohols using Cu(NO₃)₂·3H₂O and TEMPO or 4-HO-TEMPO as the catalysts forming aldehydes or ketones with an excellent selectivity has been developed.

B2pin2-catalyzed oxidative cleavage of a CC double bond with molecular oxygen

B₂pin₂-catalyzed oxidative cleavage of the CC double bond of an olefin with molecular oxygen as the oxidant and oxygen source has been developed.

A study on the prediction method of coal spontaneous combustion development period based on critical temperature

Prediction of the development and evolution process of coal spontaneous combustion is of great significance to its prevention and control. Through the testing of different metamorphic degrees coal programmed heating characteristics and the infrared functional groups, the critical temperatures of the coalification process were analyzed and a method to predict the period of spontaneous combustion was established according to the characteristic of the critical temperature change. What can be inferred from this research is that the critical temperature of activation energy of coal in programmed heating experiments can characterize the nature of coal at low temperature and the macrocritical temperature point can be obtained from the characteristics of the activation energy change during the low-temperature period. The critical point of coal functional groups in terms of its micro changes is similar to its macro changes, the absorption intensity of the characteristic peak shows a general increasing trend, with an initial decline and then increase, followed by a decrease and a subsequent increase. In the high-temperature combustion process, the activation energy is not constant and changes from a negative value to 0, then the activation energy changes to a positive value, and finally goes down to a negative value. Therefore, the prediction of development period of spontaneous combustion can be achieved through the critical temperature of activation energy which acts as the critical temperature in high-temperature combustion process, and the prediction of low-temperature oxidation process is based on the critical temperature of activation energy in programmed heating process and the macro critical temperature of absorption intensity of coal functional groups.

Pentadecanal inspired molecules as new anti-biofilm agents against Staphylococcus epidermidis

Staphylococcus epidermidis, a harmless human skin colonizer, is a significant nosocomial pathogen in predisposed hosts because of its capability to form a biofilm on indwelling medical devices. In a recent paper, the purification and identification of the pentadecanal produced by the Antarctic bacterium Pseudoalteromonas haloplanktis TAC125, able to impair S. epidermidis biofilm formation, were reported. Here the authors report on the chemical synthesis of pentadecanal derivatives, their anti-biofilm activity on S. epidermidis, and their action in combination with antibiotics. The results clearly indicate that the pentadecanal derivatives were able to prevent, to a different extent, biofilm formation and that pentadecanoic acid positively modulated the antimicrobial activity of the vancomycin. The cytotoxicity of these new anti-biofilm molecules was tested on two different immortalized eukaryotic cell lines in view of their potential applications.

Metal-Free Aerobic Oxidation of Nitro-Substituted Alkylarenes to Carboxylic Acids or Benzyl Alcohols Promoted by NaOH

Efficient and selective aerobic oxidation of nitro-substituted alkylarenes to functional compounds is a fundamental process that remains a challenge. Here, we report a metal-free, efficient, and practical approach for the direct and selective aerobic oxidation of nitro-substituted alkylarenes to carboxylic acids or benzyl alcohols. This sustainable system uses O₂ as clean oxidant in a cheap and green NaOH/EtOH mixture. The position and type of substituent critically affect the products. In addition, this sustainable protocol enabled gram-scale preparation of carboxylic acid and benzyl alcohol derivatives with high chemoselectivities. Finally, the reactions can be conducted in a pressure reactor, which can conserve oxygen and prevent solvent loss. The approach was conducive to environmental protection and potential industrial application.