Substrate-controlled and highly stereoselective synthesis of 2-aminobut-2-ene-1, 4-diones

2-Methylthio-substituted 1,4-enediones, obtained from readily available aryl methyl ketones, were reacted with primary or secondary amines to afford the desired 1,4-diaryl-2-aminobut-2-ene-1,4-diones in excellent yields with high Z/E-stereoselectivity.     

An efficient synthesis of δ-glyconolactams by intramolecular Schmidt–Boyer reaction under microwave radiation

δ-Glyconolactams were first synthesized by the intramolecular Schmidt–Boyer reaction using corresponding δ-azidosugars as starting material. The reaction could be efficiently performed in good yields of 61–69% under microwave radiation in acid condition, providing an alternative protocol to iminosugar δ-lactam.     

A new electronically deficient atropisomeric diphosphine ligand (S)-CF3O-BiPhep and its application in asymmetric hydrogenation

A new electronically deficient atropisomeric diphosphine ligand (S)-CF₃O-BiPhep was synthesized from 1-bromo-3-(trifluoromethoxy)benzene in high yield. The key steps included oxidative coupling with anhydrous ferric chloride and optical resolution by (+)-DMTA. The ligand afforded high performance for Ir-catalyzed asymmetric hydrogenation of quinolines with ee up to 92% and TON up to 25,000. It was also successfully applied to the Pd-catalyzed asymmetric hydrogenation of simple indoles with ee up to 87% and Rh-catalyzed asymmetric 1,4-addition of phenylboronic acid to 2-cyclohexenone with 97% ee.     

Corrosion inhibition of ammonium molybdate for AA6061 alloy in NaCl solution and its synergistic effect with calcium gluconate

The corrosion inhibition of ammonium heltamolybdate (AH) and calcium gluconate (CG) for AA6061 alloy in 3% NaCl solution was investigated by the electrochemical measurements. It indicates that AH inhibits the corrosion of AA6061 alloy and acts as an anodic inhibitor. Maximum inhibition efficiency reaches 74.3% at the concentration of 1 × 10^?4 mol.l^?1 AH. The results of the electrochemical studies reveal AH is physically adsorbed on the AA6061 alloy surface and the adsorption follows Langmuir isotherm. The combination of AH and CG enhances the inhibition efficiency to 95.9%. The enhanced inhibition is attributed to the promotion of AH adsorption by CG. The mixture of AH and CG is a mixed‐type inhibitor and renders the corrosion potential to more positive values. Copyright © 2011 John Wiley & Sons, Ltd.     

Copper‐catalyzed Clauson–Kass pyrroles synthesis in aqueous media

An efficient and convenient copper‐catalyzed Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with amines in aqueous media has been developed, providing a wide range of N‐substituted pyrroles in good yields. It is noteworthy that the Clauson–Kass reaction of 2,5‐dimethoxytetrahydrofuran with p‐phenylenediamine or m‐phenylenediamine proceeds smoothly to afford the corresponding monopyrroles and bispyrroles with high selectivity in impressive yields. A plausible mechanism for the formation of N‐substituted pyrroles has been proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Copolymerization of styrene and norbornene with β‐diketiminato nickel/methylaluminoxane catalytic system

Styrene–norbornene (S‐N) copolymerizations were carried out using β‐diketiminato nickel complexes CH{C(CF₃)NAr}₂NiBr (Ar = 2,6‐ⁱPr₂C₆H₃, 1 ; Ar = 2,6‐Me₂C₆H₃, 2 ) in the presence of methylaluminoxane. The influence of the comonomer feed content and polymerization temperature on the conversion and composition of the copolymers with the catalytic system was investigated. An increase in the feed ratio of S/N led to an increase in the incorporated styrene content of the resulting copolymer. NMR characterization of the copolymers generated with the catalytic systems showed that the random S‐N copolymers are produced. Differential scanning calorimetric determination of the copolymers shows higher T_g values than polystyrene, and gel permeation chromatographic measurements have shown that the copolymers possess rather narrow molecular weight distributions, suggesting that the copolymerization take place at a single active site. Copyright © 2012 John Wiley & Sons, Ltd.     

Application of alkoxide in catalytic transfer hydrogenation of unsaturated nitrogen compounds

Alcoholate was utilized in catalytic transfer hydrogenation of unsaturated nitrogen compounds. In the reduction of nitro compounds, oximes and imines, alkoxide was used as the promoter, with alcohol as the hydrogen source, while in the reduction of nitriles, alkoxide was used as the hydrogen source.     

Discontinuous crack-bridging model for fracture toughness analysis of nacre

Studying the structure–property relation of biological materials can not only provide insight into the physical mechanisms underlying their superior properties and functions but also benefit the design and fabrication of advanced biomimetic materials. In this paper, we present a microstructure-based fracture mechanics model to investigate the toughening effect due to the crack-bridging mechanism of platelets. Our theoretical analysis demonstrates the crucial contribution of this mechanism to the high toughness of nacre. It is found that the fracture toughness of nacre exhibits distinct dependence on the sizes of platelets, and the optimized ranges for the thickness and length of platelets required to achieve higher fracture toughness are given. In addition, the effects of such factors as the mechanical properties of the organic phase (or interfaces), the effective elastic modulus of nacre, and the stacking pattern of platelets are also examined. Finally, some guidelines for the biomimetic design of novel materials are proposed based on our theoretical analysis.