A catalytic asymmetric hetero-Diels-Alder (HDA) reaction has been achieved through hydrogen-bond directed γ-addition of olefinic azlactones to isatins. This methodology provides an efficient access to spirooxindole dihydropyranones in moderate to good yields and with excellent enantioselectivities.
The first organocatalytic hetero-Diels–Alder reaction of an in situ generated diene with α-keto esters was reported for the construction of chiral dihydropyranones.
The MnZn ferrite coating formed on the surface of iron-based soft magnetic powders via facile and modified sol–gel process has been fabricated to obtain better magnetic performance due to its higher permeability compared with traditional nonmagnetic insulation coatings. The influence of the MnZn ferrite contents on the magnetic performance of the soft magnetic composites (SMCs) has been studied. As the MnZn insulation content increases, the core loss first experiences a decreasing trend that is followed by progressive increase, while the permeability follows an increasing trend and subsequently degrades. The optimized magnetic performance is achieved with 2.0 wt% MnZn ferrite, which results from the decrement of inter-particle eddy current losses based on loss separation. A uniform and compact coating layer composed of MnZn ferrite and oxides with an average thickness of
0.38
±
0.08
μ
m
is obtained by utilizing ion beam technology, and the interface between the powders and the coating shows satisfied adhesiveness compared with the sample directly prepared by mechanical mixing. The evolution of the coating layers during the calcination process has been presented based on careful analysis of the composition and microstructure.
Atomically precise palladium nanoclusters show great potential applications in the field of catalysis owing to its ultrasmall size and precise structure. This work, we report the mesoporous silica nanoparticles (MSNs) supported [Pd3Cl(PPh3)3(PPh2)2]Cl catalysts (denoted as Pd3Cl/MSNs) for the reduction of 4‐nitrophenol and Heck coupling reactions of iodobenzene and styrenes. High uniform MSNs, with average diameter ≈110 nm, were prepared by sol–gel method, followed by Pd nanoclusters immobilization into the pore of MSNs. The MSNs supported Pd nanoclusters were well characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT‐IR), and diffuse reflectance optical spectrum. The results indicated that Pd3Cl nanoclusters after immobilized into the pores of MSNs are intact and possess good dispersibility. The catalytic performance of as‐prepared nanocomposites was evaluated by the reduction of 4‐nitrophenol and Heck reactions. The 4‐nitrophenol could be completely conversion to 4‐aminophenol within 6 min. Meanwhile, the as‐prepared Pd3Cl/MSNs exhibit excellent catalytic performance in the Heck reactions between iodobenzenes and styrenes. The high catalytic activity of Pd3Cl/MSNs could be attributed to the large surface area and unique geometric structure of as‐prepared Pd nanoclusters. More importantly, the catalysts could be easily recycled by centrifugation and shows excellent reusability.
The first mesoporous silica nanoparticles (MSNs) supported atomically precise palladium nanoclusters catalyzed alcohol oxidation reactions in water have been achieved. The catalysts was synthesized with simple impregnation method and well characterized by TEM, FT-IR, XPS anddiffuse reflectance optical spectrum and the results proved that the Pd nanoclustersimmobilized into the pores of MSNs.The as-prepared catalyst show excellent activity for the alcohol oxidation reactions with high yield under extremely mild aqueous conditions utilizes 1 atmosphere of molecular oxygen as sole oxidant. The features of clean system, gram-scale oxidation and easy recovery catalyst make this method cost effectively and environmentally benign.
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