Ligand-Controlled, Nickel-Catalyzed Stereodivergent Construction of 1,3-Nonadjacent Stereocenters.

In contrast to the asymmetric synthesis of molecules with a single stereocenter or 1,2-adjacent stereocenters, the simultaneous construction of acyclic 1,3-nonadjacent stereocenters via a single catalyst in an enantioselective and diastereoselective manner remains a formidable challenge. Here, we demonstrate the enantioselective and diastereodivergent construction of 1,3-nonadjacent stereocenters through Ni-catalyzed reductive cyclization/cross-coupling of alkene-tethered aryl bromides and α-bromoamides, which represents the major remaining stereochemical challenge of cyclization/difunctionalization of alkenes. Using Ming-Phos as ligand, a diverse set of oxindoles containing 1,3-nonadjacent stereocenters were obtained with high levels of enantio- and diastereoselectivity. Mechanistic experiments and density functional theory calculations indicate that magnesium salt plays a key role in controlling the diastereoselectivity. Furthermore, another set of complementary stereoisomeric products were constructed from the same set of starting materials using Ph-Phox as ligand.

Photochemical Mn-Mediated Generation of Azide Radicals for Improvement of Alkene Hydroxyazidation.

State-of-the-art strategies for alkene-hydroxyazidation, which yield a mixture of ß-azido alcohol and ß-azido peroxide, must rely on phosphine reagents to improve the chemoselectivity. To overcome the above problems, we present a photochemical hydroxyazidation of alkenes via Mn-mediated ligand-to-metal charge transfer (LMCT) in O2, which activates N3- to •N3 and incorporates O2 to be used as an oxygen source in the hydroxyazidation products. Broad alkene range and step-economy chemistry for the hydroxyazidation transformation were also demonstrated.

Nickel-Catalyzed Defluorinative Asymmetric Cyclization of Fluoroalkyl-Substituted 1,6-Enynes for the Synthesis of Seletracetam.

The introduction of fluorine-containing groups into organic molecules can significantly affect their physical and chemical properties and has long been used as an effective strategy for drug discovery and development. Consequently, the development of catalytic asymmetric methods for the synthesis of fluorine-containing heterocycles is highly desirable and sought after. Herein, we describe a nickel-catalyzed defluorinative asymmetric cyclization of fluoroalkyl-substituted 1,6-enynes, providing an expedient access to synthetically attractive 4-fluorovinyl-substituted 2-pyrrolidones in good yields with remarkable high levels of chemo-, regio-, and enantioselectivities (90-99 % ee,>35 examples). This protocol features readily available starting materials and excellent functional group compatibility, and exhibits complementary regioselectivity. The utility of this strategy was demonstrated in the enantioselective synthesis of the antiepileptic drug Seletracetam.

Nickel-Catalyzed Asymmetric Reductive Carbo-Carboxylation of Alkenes with CO2.

Reductive carboxylation of organo (pseudo)halides with CO2 is a powerful method to provide carboxylic acids quickly. Notably, the catalytic reductive carbo-carboxylation of unsaturated hydrocarbons via CO2 fixation is a highly challenging but desirable approach for structurally diverse carboxylic acids. There are only a few reports and no examples of alkenes via transition metal catalysis. We report the first asymmetric reductive carbo-carboxylation of alkenes with CO2 via nickel catalysis. A variety of aryl (pseudo)halides, such as aryl bromides, aryl triflates and inert aryl chlorides of particular note, undergo the reaction smoothly to give important oxindole-3-acetic acid derivatives bearing a C3-quaternary stereocenter. This transformation features mild reaction conditions, wide substrate scope, facile scalability, good to excellent chemo-, regio- and enantioselectivities. The method highlights the formal synthesis of (-)-Esermethole, (-)-Physostigmine and (-)-Physovenine, and the total synthesis of (-)-Debromoflustramide B, (-)-Debromoflustramine B and (+)-Coixspirolactam A; thereby, opening an avenue for the total synthesis of chiral natural products with CO2 .

Ni-Catalyzed Reductive Arylacylation of Alkenes toward Carbonyl-Containing Oxindoles.

An easy-to-handle Ni-catalyzed three-component reductive arylacylation of alkenes using isobutyl chloroformate as a CO source was described. This reaction operates under mild reaction conditions without the need to use toxic CO gas or metal carbonyl reagents. In addition, this method allows for rapid synthesis of 3,3-disubstituted oxindoles with an all-carbon quaternary stereocenter containing a ketone group in good yields with broad substrate scope.

Ni-Catalyzed Enantioselective Reductive Diarylation of Activated Alkenes by Domino Cyclization/Cross-Coupling.

A Ni-catalyzed enantioselective reductive diarylation of activated alkenes by domino cyclizative/cross-coupling of two aryl bromides is developed. This reaction proceeds under very mild conditions and shows broad substrate scope, without requiring the use of preformed organometallic reagents. Moreover, this approach provides direct access to various bis-heterocycles bearing all-carbon quaternary centers in synthetically useful yields (up to 81%) with excellent enantioselectivity (>30 examples, 90-99% ee).

Visible-Light-Promoted Oxidative Amidation of Bromoalkynes with Anilines: An Approach to α-Ketoamides.

A convenient and practical synthetic route to α-ketoamides from bromoalkynes and anilines through phototriggered organic transformations via a C-N cross-coupling and an oxidation of C≡C was developed. The reaction could be furnished without an external photocatalyst at ambient conditions, and a wide range of α-ketoamides were obtained in good yields.

Nickel-Catalyzed Domino Heck Cyclization/Suzuki Coupling for the Synthesis of 3,3-Disubstituted Oxindoles.

The first nickel-catalyzed domino Heck cyclization/Suzuki coupling reaction for the synthesis of 3,3-disubstituted oxindoles bearing quaternary all-carbon centers is reported. A wide range of electrophiles, such as aryl iodides, bromides, triflates, and chlorides, are all compatible with the reaction conditions. Moreover, cheap aryl esters, which undergo catalytic C-O bond cleavage, could also be employed as electrophiles. The approach shows good yields and broad scope, complementing a more practical and sustainable alternative to the conventional palladium-based analogues.

Visible-Light-Promoted [2 + 2 + 2] Cyclization of Alkynes with Nitriles to Pyridines Using Pyrylium Salts as Photoredox Catalysts.

A highly regioselective [2 + 2 + 2] cyclization of aromatic alkynes with nitriles is developed for the preparation of 2,3,6-trisubstituted pyridines under visible-light irradiation using a pyrylium salt as the photoredox catalyst. This cycloaddition is achieved through a photooxidative single-electron-transfer process at room temperature and under metal-free conditions. A variety of aromatic alkynes and nitriles are employed to furnish the annulation products in good yields.

Visible-Light-Initiated Na2-Eosin Y Catalyzed Highly Regio- and Stereoselective Difunctionalization of Alkynes with Alkyl Bromides.

A highly regioselective and stereoselective addition of alkyl bromides (amino-brominated aromatic ß,ß-dicyanoalkenes) to arylacetylenes by photoredox catalysis was developed. This difunctionalization of arylacetylenes was accomplished under ambient and metal-free conditions to produce alkenyl bromides in high efficiency with a wide range of group tolerance.

Preparation and Biosafety Assessment of Water-Soluble Hyperbranched Polyester Nanoparticles with Carboxylic Acid Functional Groups.

Biosafety assessment of nanoparticles has been of great interest in the development of nanoscience and nanotechnology. Here, the water-soluble hyperbranched polyester nanoparticles with carboxylic acid functional group (HBPE-CA NPs) are synthesized and characterized. They have amphiphilic structure that include hydrophobic hyperbranched polyester (HBPE) core and hydrophilic carboxylated terminal groups. Biosafety assessment tests of the HBPE-CA NPs include coagulation times, hemolysis, complement activation, platelet activation and cytotoxicity (MTT) are performed. The results show that the HBPE-CA NPs exhibit good hemocompatibility that strongly depend on the amphiphilic structure. Moreover, the results also indicate the non-cytotoxicity of the HBPE-CA NPs. So the HBPE-CA NPs provide a promising platform of blood circulation system for illness therapy with the help of the drug-loaded capacity of-HBPE.

[Biosynthetic schwertmannite as catalyst in Fenton-like reactions for degradation of methyl orange].

Biosynthesized schwertmannite was used as catalyst in photo-Fenton-like reaction to facilitate the degradation of methyl orange (MO). Schwertmannite was synthesized through the oxidation of FeSO4 by Acidithiobacillus ferrooxidans LX5 cell suspension at an initial pH 2.5 and 28 degress C for 3 days and characterized using X-ray diffraction spectroscopy and scanning electron microscope. The oxidative degradation of MO in the photo-Fenton-like reaction was studied at different initial pH values of suspension, concentrations of H2O2 and dosages of catalyst. The results suggested that the biosynthetic schwertmannite showed a good catalytic activity in the MO degradation via *OH radical mechanism. Considerable degradation efficiency of MO was still obtained in approximately neutral condition or in the presence of high concentrations of chloride, sulfate and nitrate. This work demonstrated that the heterogeneous photo-Fenton-like reaction catalyzed by the biosynthetic schwertmannite is a promising advanced oxidation technology for the treatment of wastewater containing MO.

(n)Bu3P-catalyzed desulfonylative [3 + 2] cycloadditions of allylic carbonates with arylazosulfones to pyrazole derivatives.

Highly efficient (n)Bu3P-catalyzed desulfonylative [3 + 2] cycloadditions of allylic carbonates with arylazosulfones were developed for the synthesis of pyrazole derivatives. The reactions proceed smoothly under mild conditions to generate corresponding annulation products in good to excellent yields.

Laccase biosensor based on phytic acid modification of nanostructured SiO2 surface for sensitive detection of dopamine.

In this work, three kinds of nanostructured silica-phytic acid (SiO2-PA) materials with diverse morphologies including spherical SiO2-PA (s-SiO2-PA), rod-like (r-SiO2-PA), and helical SiO2-PA (h-SiO2-PA) were prepared with the help of electrostatic interaction. The SiO2-PA nanomaterials with different morphologies were characterized by using transmission electron microscopy (TEM), Fourier transform infrared (FTIR), electrochemical impedance spectroscopy (EIS), and circular dichroism spectrum (CD). Diverse morphologies of SiO2-PA were used as electrode decorated materials to achieve a high efficiency for electrochemical dopamine (DA) detection. The laccase biosensors were fabricated by immobilizing different morphologies of SiO2-PA nanomaterials and laccase onto the glassy carbon electrode (GCE) surface, successively. Then the electrochemical responses of the different morphologies of nanostructured SiO2-PA nanomaterials to laccase were discussed. Results indicated that compared to laccase/s-SiO2-PA and laccase/r-SiO2-PA, the laccase/h-SiO2-PA-modified electrode showed the best electrochemical performances.

[Clinical applications of the neurocutaneous axial flap pedicled with perforating vessels].

OBJECTIVE: To report the operative technique and clinical results of the neurocutaneous vascular axial flap with perforating vessels as its pedicle. METHODS: An axial skin flap was designed along the axis of small paraneural vessels that was close to a concomitant cutaneous nerve. The cutaneous perforating branches of major arteries were used as the pedicle, which provided a rotation arc for the flap to cover the defects in the distal site of extremities. 43 neurocutaneous vascular axial flaps were transferred, including 13 sural neurocutaneous axial flaps (30 cm x 12 cm to 16 cm x 8 cm) supplied by perforating branches of the peroneal vessel; 9 saphenous neurocutaneous axial flaps (15 cm x 8 cm to 5 cm x 4 cm) with posterior tibial perforators as the pedicle; 8 posterior antebrachial neurocutaneous axial flaps (16 cm x 6 cm to 10 cm x 4 cm) based on the dorsal branch of the anterior interossea vessel and 13 reversed neurocutaneous axial flaps (6.0 cm x 3.5 cm to 2.5 cm x 1.5 cm) on the dorsal hand pedicled with the perforators at the interdigital web space. RESULTS: 42 flaps survived completely. One flap underwent venous congestion with necrosis on the distal one fourth of the flap. The color and texture of the flaps were good. The appearance and functional results were satisfactory as revealed by follow-up for 6 to 24 months. CONCLUSIONS: The modified operation combines the advantages of both the perforator flap and the neurocutaneous axial flap, enlarges the size of the flap and extends the scope of reconstruction. The flap is characterized with delicate designation, easy dissection and reliable blood supply. It is a good method in repairing the skin defects of the extremities.