Palladium-Catalyzed Regioselective Olefination of O-Acetyl Cyanohydrins.

A practical palladium-catalyzed ortho-olefination of O-acetyl cyanohydrins assisted by synergetic directing groups has been developed. Thus, a range of olefinated O-acetyl cyanohydrins were synthesized in moderate to good yields. The reaction occurs efficiently with high regioselectivity and with a satisfactory tolerance of functional groups.

Chelation versus Non-Chelation Control in the Stereoselective Alkenyl sp2 C-H Bond Functionalization Reaction.

A hydroxy group chelation-assisted stereospecific oxidative cross-coupling reaction between alkenes was developed under mild reaction conditions. In the presence of palladium catalyst, the alkenes tethered with hydroxy functionality can couple efficiently with electron-deficient alkenes to form the corresponding multi-substituted olefin products. The hydroxy group on the substrate could play dual roles in reaction, acting as the directing group for alkenyl C-H bond activation and controlling the stereoselectivity of the products.

Addition of optically pure H-phosphinate to ketones: selectivity, stereochemistry and mechanism.

Aromatic methyl ketones and cyclic asymmetric ketones underwent hydrophosphorylation with P-stereogenic H-P species in the presence of potassium carbonate to produce P,C-stereogenic tertiary α-hydroxyl phosphinates in excellent yields with up to 99 : 1 dr. The diastereoselectivity was induced by a reversible conversion of less stable stereomer of product to that of a more stable one via an equilibrium, which was confirmed by aldehyde/ketone exchanging reaction. Toward the exchange, aliphatic or aldehyde carbonyl were more active than aromatic or ketone carbonyls, respectively. The stability difference between the two diastereomers was controlled by the sizes of substituents linking to phosphorus or α-carbon.

In situ quantitative analysis by ultrasonic extraction and nebulization combined with hydrogen flame ionization mass spectrometry: Diisopropylnaphthalene (DIPN), a marker of recycled paper in packing materials.

Ambient mass spectrometry is used for direct analysis and high-throughput screening in many fields. However, most researches are about qualitative analysis. Quantitative detection based on AMS only performs on standard compounds and the relative standard deviation is so large that the accuracy of the result is low. In this study, a hydrogen flame ion source with ultrasonic nebulizer as sampling unit was established to enable solid samples to extract, nebulize and quantitatively detect in situ, with high sensitivity. This device was used to quantificationally determine the content of diisopropylnaphthalene (DIPN) in food packaging paper to identify recycled paper. Rapid analysis was performed in situ without complex pretreatment and the whole analysis time was less than 10 min. It's environmentally friendly that only 100 mg (or less) of sample and no more than 1 mL of solvent are required for one test. The external standard method was used for quantitative determination. The limit of detection was measured to be as low as 0.01 ng mL-1 and the linear dynamic range was 0.03-0.60 µg mL-1 in positive multiple reactions monitoring mode. It has been successfully applied to detect actual samples and the content of DIPN was 0.020-0.095 mg kg-1.

Chrysene, a four-ring polycyclic aromatic hydrocarbon, induces hepatotoxicity in mice by activation of the aryl hydrocarbon receptor (AhR).

Polycyclic aromatic hydrocarbons (PAHs) are a group of persistent organic global environmental pollutants and cause harmful effects on human health. Here, we evaluated adverse effects of chrysene, which is a four-ring PAH and an important member of 16 priority PAHs, on the liver. Chrysene was detected in some common raw and cooked Chinese food samples. Hepatotoxicity including increased relative liver weight, hepatocyte swelling and degeneration, and elevated serum alanine aminotransferase (ALT) levels were observed in chrysene-exposed C57BL/6 mice. Glutamine treatment effectively ameliorated chrysene-induced mice liver injury by decreasing serum ALT levels. Chrysene induced mice hepatic glutathione depletion and oxidative DNA damage with increased 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels. Hepatic expression levels of the aryl hydrocarbon receptor (AhR), AhR-related target genes including CYP1A1, CYP1A2 and CYP1B1, and AhR nuclear translocator (ARNT) were significantly increased in chrysene-exposed C57BL/6 mice. Chrysene induced mice hepatic mRNA levels of the nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2-mediated phase II detoxifying and antioxidant enzymes including NQO1, UGT1A1, UGT1A6, SULT1A1, GSTm1, GSTm3, Catalase (CAT), GPx1, and SOD2. We found that chrysene had toxic effects including increased relative liver weight and elevated serum ALT levels on AhR+/+ mice but not AhR-/- mice. Chrysene significantly induced hepatic mRNA levels of CYP1A1 and CYP1A2 in AhR+/+ mice but not AhR-/- mice. To our knowledge, this study is the first to demonstrate that hepatotoxicity causes by chrysene is dependent on AhR, and Nrf2 plays an important regulation role in protection against oxidative liver injury induced by chrysene.

Palladium-catalyzed silaborative carbocyclizations of 1,6-diynes.

An addition/cyclization reaction of 1,6-diynes was developed for the synthesis of highly substituted 1,2-dialkylidenecycloalkanes. In this work, 1,6-diynes reacted with (dimethylphenylsilyl)pinacol-borane in the presence of a palladium catalyst to afford 1,2-dialkylidenecycloalkanes bearing silyl and boryl groups with a (Z,Z)-configuration in good to excellent yields. Moreover, the corresponding products could be easily converted into other synthetically useful compounds. This protocol provides an efficient and practical method of heteroelement-element linkage addition to the unsaturated 1,6-diynes.

Copper-Catalyzed Dehydrogenative Diels-Alder Reaction.

A practical and effective copper-catalyzed dehydrogenative Diels-Alder reaction of gem-diesters and ketone with dienes has been established. The active dienophiles were generated in situ via a radical-based dehydrogenation process, which reacted with a wide variety of dienes to afford various polysubstituted cyclohexene derivatives in good to excellent yields.

Palladium-Catalyzed Direct Intramolecular C-N Bond Formation: Access to Multisubstituted Dihydropyrroles.

A palladium-catalyzed intramolecular amination of alkenes with retention of olefin functionalization was achieved under mild reaction conditions. In the presence of palladium catalyst, the tosyl-protected amine can directly couple with a double bond to provide versatile dihydropyrrole derivatives in moderate to excellent yields.

Palladium-catalyzed difunctionalization of internal alkynes via highly regioselective 6-endo cyclization and alkenylation of enynoates: synthesis of multisubstituted pyrones.

An efficient Pd(II)-catalyzed difunctionalization reaction of internal alkynes is reported. In this reaction, various enynoates and electron-deficient alkenes were used for the syntheses of useful highly substituted pyrone derivatives via a 6-endo cyclization and subsequent alkenylation pathway. The corresponding products could be obtained in moderate to good yields under very mild reaction conditions. The high regioselectivity and wide compatibility with different functional groups found in the desired products demonstrate this method to be a general and useful tool for the synthesis of highly substituted pyrone derivatives.