Photoinduced Transition-Metal and External Photosensitizer Free Benzylic Fluorination of Unactivated Alkylarenes.

A green and efficient protocol for the direct monofluorination of unactivated alkylarenes under visible-light irradiation has been developed, without any extraneous transition-metal catalysts or photosensitizers. This method is compatible with a broad spectrum of functional groups, including carboxylic and alcoholic scaffolds, under mild reaction conditions. Gram-scale synthesis of a fluorine-containing pharmaceutical analogue was successfully executed, underscoring the strategy's reliability and practicality. Furthermore, mechanistic studies suggest that a single-electron transfer mechanism might be responsible for the generation of the benzylic radicals in initiation step.

Synthesis of 3-substituted 2-oxindoles from secondary α-bromo-propionanilides via palladium-catalyzed intramolecular cyclization.

In contrast to aromatic halides, coupling reactions involving oxidative addition of alkyl halides, especially secondary or tertiary halides, to transition metals tend to be more challenging. Herein a palladium-catalyzed intramolecular cyclization of α-bromo-propionanilides has been developed, delivering a series of 3-substituted 2-oxindoles in high yields. The method features easy to prepare starting materials, broad substrate scope and excellent functional group tolerance. A detailed mechanistic investigation has been performed.

Synergistic Relay Reactions To Achieve Redox-Neutral α-Alkylations of Olefinic Alcohols with Ruthenium(II) Catalysis.

Herein, we report a ruthenium-catalyzed redox-neutral α-alkylation of unsaturated alcohols based on a synergistic relay process involving olefin isomerization (chain walking) and umpolung hydrazone addition, which takes advantage of the interaction between the two rather inefficient individual reaction steps to enable an efficient overall process. This transformation shows the compatibility of hydrazone-type "carbanions" and active protons in a one-pot reaction, and at the same time achieves the first Grignard-type nucleophilic addition using olefinic alcohols as latent carbonyl groups, providing a higher yield of the corresponding secondary alcohol than the classical hydrazone addition to aldehydes does. A broad scope of unsaturated alcohols and hydrazones, including some complex structures, can be successfully employed in this reaction, which shows the versatility of this approach and its suitability as an alternative, efficient means for the generation of secondary and tertiary alcohols.

Oxidation of Enones for Regioselective [3+2] Cycloaddition through γ-Enone Radical Intermediates.

Invited for the cover of this issue is the group of Min Zhang and Weiping Su at the Fujian Institute of Research on the Structure of Matter. Read the full text of the article at 10.1002/chem.201903551.

Oxidation of Enones for Regioselective [3+2] Cycloaddition through γ-Enone Radical Intermediates.

Herein, an oxidization reaction of enones with a CuII complex that leads to a new type of regioselective [3+2] cycloaddition is reported. Highly functionalized cyclopentenes and spirocyclic compounds are obtained in moderate-to-good yields. This cycloaddition reaction occurred through the formation of γ-enone radicals, providing a rarely explored reactivity pattern for enones.

On the blistering of thermo-sensitive hydrogel: the volume phase transition and mechanical instability.

This paper explores the physical mechanisms responsible for the appearance of small blisters on the surface of temperature sensitive hydrogels as they deswell rapidly during their volume phase transition. For this, we develop a numerical model that couples the processes of hydrogel deswelling and blister growth due to the existence of a thin quasi-impermeable layer on its surface. The model points out that blister inflation originates at defects point under the gel's surface, under the effect of the increasing osmotic pressure in the gel as it undergoes its phase transition. Due to their large deformation, these blisters often experience a mechanical instability that triggers a sudden increase in their growth rate at the expense of their closest neighbors. Using a simple computational model, we then show that blisters are able to communicate via internal pressure and that these interactions are mediated by two characteristic time scales related to solvent transport within and between adjacent blisters. Our study finally indicates that these mechanisms can be controlled by temperature and the gel's cross-link density to achieve diversity of blister patterns on the gel's surface. The proposed analysis provides predictions that agree well with experimental observations of NiPAm gels which deswell in various conditions.

Silver-catalyzed arylation of (hetero)arenes by oxidative decarboxylation of aromatic carboxylic acids.

A long-standing challenge in Minisci reactions is achieving the arylation of heteroarenes by oxidative decarboxylation of aromatic carboxylic acids. To address this challenge, the silver-catalyzed intermolecular Minisci reaction of aromatic carboxylic acids was developed. With an inexpensive silver salt as a catalyst, this new reaction enables a variety of aromatic carboxylic acids to undergo decarboxylative coupling with electron-deficient arenes or heteroarenes regardless of the position of the substituents on the aromatic carboxylic acid, thus eliminating the need for ortho-substituted aromatic carboxylic acids, which were a limitation of previously reported methods.

Umpolung carbonyls enable direct allylation and olefination of carbohydrates.

Mother Nature has its own arts to build a vast number of carbohydrates; however, there is still a lack of tools for selective functionalization of native carbohydrates through C─C bond formation. Such a long-standing challenge for the synthetic community lies into the intrinsic problems related to the innate properties of carbohydrates, e.g., the ease to oligomerization or polymerization, the difficulty of chemoselectivity control in the presence of multiple hydroxyl groups, the great challenge to retain the multiple chiral centers during the transformation, etc. Here, by applying an umpolung strategy of carbohydrate carbonyls, we report a direct deoxygenative allylation and olefination of carbohydrates to tackle the abovementioned issues. The reaction is compatible with a wide range of natural carbohydrates, providing a direct synthetic method to use carbohydrates as multiple C-centered chiral synthons to achieve C─C bond cross-coupling reactions. Furthermore, the synthetic applicability is demonstrated by late-stage modifications of natural products and pharmaceutical derivatives.

Pd/PR3-catalyzed cross-coupling of aromatic carboxylic acids with electron-deficient polyfluoroarenes via combination of decarboxylation with sp2 C-H cleavage.

By using Pd(TFA)(2)/PCy(3) as a catalyst, a broad range of aromatic carboxylic acids, including heteroaromatic carboxylic acids, efficiently underwent decarboxylative coupling with an array of polyfluoroarenes in the presence of stoichiometric amount of silver salts to generate biaryls. Silver salts were adjusted to the reactivity of aromatic carboxylic acids to efficiently suppress the protodecarboxylation and therefore improve decarboxylative cross-couplings. It was established that the palladium complex containing the PCy(3) ligand was capable of catalyzing the decarboxylation of electron-rich aromatic carboxylic acids, and silver salts promoted the decarboxylation of both electron-rich and -deficient ones. To explain the two different decarboxylation processes, two possible reaction pathways are proposed, which were further supported by the facts that the stoichiometric arylpalladium complex can directly arylate pentafluorobenzene in the presence of PCy(3) and the arylpalladium complex can catalyze the decarboxylative coupling of 2,4-dimethoxybenzoic acid with pentafluorobenzene. The kinetic isotope effect of 4.0 clearly showed that the C-H bond cleavage of polyfluoroarenes is involved in the rate-determining step.

Copper-catalyzed direct alkynylation of electron-deficient polyfluoroarenes with terminal alkynes using O2 as an oxidant.

A copper-catalyzed direct alkynylation of electron-deficient polyfluoroarenes with a wide range of terminal alkynes is realized for the first time. The reaction proceeds under mild conditions with O(2) as an oxidant.

[Effect of powder's particle size on the quantitative prediction of volatile oil content in Zanthoxylum bungeagum by NIR technique].

The traditional chemical methods to measure the volatile oil content of zanthoxylum bungeagum encounter some problems such as long time and low efficiency, so it is difficult to achieve rapid detection. One hundred forty-one samples including 74 zanthoxylum bungeagum maxim and 67 zanthoxylum schinifolium Sieb. et zucc were collected, from many provinces in China such as Shan Xi, Si Chuan, Gan Su, Chong Qing, Yun Nan, etc. Each sample was crushed and sorted to 8 kinds of powder samples according to the particle size of 120-mesh, 100-mesh, 80-mesh, 60-mesh, 40-mesh, 20-mesh, 10-mesh, respectively, including the material retained by the 10-mesh sieve. Then, each powder sample was labeled by one of the following serial numbers: 120, 100, 080, 060, 040, 020, 010 and 000. For each sample, the NIR spectra of 8 different kinds of particle size powders were measured using a Bruker MATRIX-I FT-NIR spectrometer. Then, the 8 different kinds of particle size powders of each sample were mixed uniformly. The volatile oil content was measured in each sample according to the distillation stipulated by the Forestry Standard of PRC-Quality Classify of Prickly Ash (LY/T 1652-2005). Based on near infrared spectroscopy technique and partial least squares (PLS), 8 calibration models of predicting volatile oil content were established by 141 powder samples with 8 different kinds of particle size. Experiments indicatd that the model was the best with the powder's particle size of 40-mesh and the determination coefficient (r2(141)) and the root mean square error of cross validation (RMSECV141) were 0.9364 and 0.421, respectively. The model was established by the calibration set with 105 samples with particle size of 40-mesh. Applying the model to the test set with 36 samples, the determination coefficient (r2(36)), the root mean square error of prediction (RMSEP36), the relative standard deviation (RSD36), and the ratio of prediction to deviation (RPD36) were 0.9233, 0.452, 11.66%, and 3.624, respectively. The model, based on the same sample set but optimized by OPUS 5.0, was developed by spectral data pretreatment of the Mean Centering+Vector Normalization in the spectral region of 6 100.1-5 774.2 cm(-1) and 4 601.6-4 424.2 cm(-1). Using the model to predict the test set, r2(36), RMSEP36, RSD36, and RPD36 were 0.9862, 0.192, 4.95%, and 8.517, respectively. The results showed that the model built by samples passed through 40-mesh screen was the best and rapid detection of volatile oil content in zanthoxylum bungeagum by NIR was feasible and efficient.

Photo-driven redox-neutral decarboxylative carbon-hydrogen trifluoromethylation of (hetero)arenes with trifluoroacetic acid.

Catalytic oxidative C-H bond functionalization reactions that proceed without requiring stoichiometric amounts of external oxidants or pre-functionalized oxidizing reagents could maximize the atom- and step-economy in chemical syntheses. However, such a transformation remains elusive. Here, we report that a photo-driven catalytic process enables decarboxylative C-H trifluoromethylation of (hetero)arenes with trifluoroacetic acid as a trifluoromethyl source in good yields in the presence of an external oxidant in far lower than stoichiometric amounts (for example, 0.2 equivalents of Na2S2O8) using Rh-modified TiO2 nanoparticles as a photocatalyst, in which H2 release is an important driving force for the reaction. Our findings not only provide an approach to accessing valuable decarboxylative C-H trifluoromethylations via activation of abundant but inert trifluoroacetic acid towards oxidative decarboxylation and trifluoromethyl radical formation, but also demonstrate that a photo-driven catalytic process is a promising way to achieve external oxidant-free C-H functionalization reactions.

Antioxidant Activity and Characterization of One New Polysaccharide Obtained from Perigord Truffle (Tuber huidongense).

As a medicinal and edible fungus parasitizing on the trees, Perigord Truffle (Tuber huidongense) is well known for its delicious taste, unique smell, and high medical value for healthcare. One new water-soluble nonstarch polysaccharide (PST-W with the yield of 0.41%) from Perigord Truffle (Tuber huidongense) was purified and identified on structural characteristics for the first time. The characterizations of PST-W were studied on physicochemical properties, main components of monosaccharide(s), and molecular structure. The monosaccharide compositions of PST-W were studied and identified as glucan, only containing D-glucoses with the molecular structure of [→6) α-D-Glcp (1 → 6) α-D-Glcp (1→] n by methylation analysis and NMR. In the determination of total reducing capacity, the reducing abilities of polysaccharide extracts could be listed as vitamin C > PST-W > crude polysaccharides-3 > crude polysaccharides-2 > crude polysaccharides-1. All of PST-W, crude polysaccharides-2, and crude polysaccharides-3 were relatively good scavenger for 1,1-Diphenyl-2-picrylhydrazyl radical 2,2-Diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl radicals with IC50 of 2.81, 4.17, and 3.44 mg/mL, respectively. However, O2 (-∙) clearing abilities of PST-W and crude polysaccharides were obviously weaker. The activities of total crude extract were the worst, indicating that the impurities might negatively affect the antioxidant activity. Thus, the separation and purification of polysaccharides were significant to increase the antioxidant activity in some degree.

Sensitive determination of nucleic acids using organic nanoparticle fluorescence probes.

This paper describes the preparation of organic nanoparticles by reprecipitation method under sonication and vigorous stirring. Transmission electron microscopy (TEM) was used to characterize the size and size distribution of the luminescent nanoparticles. Their average diameter was about 25 nm with a size variation of +/-18%. The fluorescence decay lifetime of the nanoparticles also was determined on a self-equipped fluorospectrometer with laser light source. The lifetime (approximately 0.09 micros) of nanoparticles is about three times long as that of the monomer. The nanoparticles were in abundant of hydrophilic groups, which increased their miscibility in aqueous solution. These organic nanoparticles have high photochemical stability, excellent resistance to chemical degradation and photodegradation, and a good fluorescence quantum yield (25%). The fluorescence can be efficiently quenched by nucleic acids. Based on the fluorescence quenching of nanoparticles, a fluorescence quenching method was developed for determination of microamounts of nucleic acids by using the nanoparticles as a new fluorescent probe. Under optimal conditions, maximum fluorescence quenching is produced, with maximum excitation and emission wavelengths of 345 and 402 nm, respectively. Under optimal conditions, the calibration graphs are linear over the range 0.4-19.0 microgml(-1) for calf thymus DNA (ct-DNA) and 0.3-19.0 microgml(-1) for fish sperm DNA (fs-DNA). The corresponding detection limits are 0.25 microgml(-1) for ct-DNA and 0.17 microgml(-1) for fs-DNA. The relative standard deviation of six replicate measurements is 1.3-2.1%. The method is simple, rapid and sensitive with wide linear range. The recovery and relative standard deviation are very satisfactory.

Ambient-Temperature Ortho C-H Arylation of Benzoic Acids with Aryl Iodides with Ligand-Supported Palladium Catalyst.

The ambient-temperature ortho C-H arylation of electron-deficient benzoic acids with aryl iodides has been achieved by using an Ac-Ile-OH-supported Pd catalyst. A wide range of unactivated benzoic acids could cross-couple an array of aryl iodides in moderate to excellent yields. The choice of HFIP as a solvent is crucial to realizing the mild C-H arylation, and the beneficial effect of the ligand on the reaction likely stems from the accelerated C-H activation process and the improved catalyst lifetime.

Inhibitory effects of resistant starch (RS3) as a carrier for stachyose on dextran sulfate sodium-induced ulcerative colitis in C57BL/6 mice.

The aim of this study was to determine the effects of resistant starch 3 (RS3) as a carrier for stachyose on dextran sulfate sodium (DSS)-induced colitis in C57BL/6 mice. RS3 microspheres carrying stachyose (RS3 + stachyose) were produced and evaluated as a potentially improved colitis therapy for this study. The body weights of the mice treated with RS3 + stachyose were higher compared with those of DSS-treated control mice. RS3 + stachyose reduced the levels of the serum pro-inflammatory cytokines IL-6 and TNF-α to a greater extent compared with the same concentration of stachyose combined with ordinary starch (stachyose + starch). Histopathological examination of sections of colon tissues showed that the RS3 + stachyose group recovered well from colitis; however, the tissue sections of the stachyose + starch group presented necrosis to a more serious degree. These results suggest that stachyose with an RS3 carrier has better preventative effects on colitis than stachyose alone in mice.

Pd-catalyzed decarboxylative arylation of silyl enol ester sp3 ß-C-H bond under aerobic conditions.

Pd-catalyzed aerobic oxidative coupling of various benzoic acids with silyl enol esters proceeds via a combination of decarboxylation with sp(3) ß-C-H bond activation to give Heck-type products. Mechanistic studies reveal this coupling involves in situ generation of olefin from aerobic oxidation of silyl enolate, followed by decarboxylative Heck coupling.

Pd-catalyzed cross-coupling of carboxylic acids with nitroethane via combination of decarboxylation and dehydrogenation.

An unexpected coupling reaction of arene carboxylic acid with nitroethane via a combination of decarboxylation and dehydrogenation is described. The method provides exclusively (E)-beta-nitrostyrenes.

Pd(O2CCF3)2/benzoquinone: a versatile catalyst system for the decarboxylative olefination of arene carboxylic acids.

A versatile palladium catalyst system was developed to effect the decarboxylative Heck coupling of a variety of arenecarboxylic acids with a wide range of olefins. The key to obtaining the efficient catalyst system is the use of 1-adamatanecarboxylic acid as additive. Alkyl-substituted olefins with coordinating groups were observed to provide significantly improved regioselectivity compared with other alkyl-substituted olefins lacking coordinating groups, and the acetate group of allylic ester was also tolerated in this reaction.

Palladium-catalyzed direct arylation of electron-deficient polyfluoroarenes with arylboronic acids.

The palladium-catalyzed direct arylation of electron-deficient arenes that contain two or more fluorine groups with arylboronic acids was realized. The key to achieving a broad substrate scope with respect to both polyfluorobenzenes and arylboronic acids is the choice of bases depending on acidities of polyfluorobenzenes.