Copper-Catalyzed Cascade 1,4-Addition/Annulation/Hydrolysis of Propargylamines with 2-Hydroxynaphthalene-1,4-diones: Direct Formation of 12-Phenacyl-11H-benzo[b]xanthenes.

A novel and versatile approach to construct 12-phenacyl-11H-benzo[b]xanthene-6,11(12H)-dione derivatives through copper-catalyzed cascade reaction of propargylamines with 2-hydroxynaphthalene-1,4-diones has been developed. The procedure is proposed to go through a sequence of 1,4-conjugate addition, intramolecular nucleophilic addition/dehydration, and hydrolysis of alkyne followed by an enol-ketone tautomerization. The reaction provides a new and highly efficient method for the synthesis of 12-phenacyl-11H-benzo[b]xanthene-6,11(12H)-diones by formation of three new bonds and one heterocycle from readily available starting materials in good to high yields (70-88%) with broad functional group compatibility in a single step.

Synthesis of 4-styrylcoumarins via FeCl3-promoted cascade reactions of propargylamines with ß-keto esters.

A versatile and highly regioselective FeCl3-promoted tandem cyclization reaction of in situ generated alkynyl o-quinone methides (o-AQMs) with ß-keto esters has been developed on the basis of the mode involving an intermolecular 1,4-conjugate addition/alkyne-allene isomerization/intramolecular transesterification/isomerization cascade. Using this method, a variety of diversely substituted 4-styryl-2H-chromen-2-ones were prepared with good efficiency and exclusive site-selectivity.

Electrochemical-reaction-induced synaptic plasticity in MoOx-based solid state electrochemical cells.

Solid state electrochemical cells with synaptic functions have important applications in building smart-terminal networks. Here, the essential synaptic functions including potentiation and depression of synaptic weight, transition from short- to long-term plasticity, spike-rate-dependent plasticity, and spike-timing-dependent plasticity behavior were successfully realized in an Ag/MoOx/fluorine-doped tin oxide (FTO) cell with continual resistance switching. The synaptic plasticity underlying these functions was controlled by tuning the excitatory post-synaptic current (EPSC) decay, which is determined by the applied voltage pulse number, width, frequency, and intervals between the pre- and post-spikes. The physical mechanism of the artificial synapse operation is attributed to the interfacial electrochemical reaction processes of the MoOx films with the adsorbed water, where protons generated by water decomposition under an electric field diffused into the MoOx films and intercalated into the lattice, leading to the short- and long-term retention of cell resistance, respectively. These results indicate the possibility of achieving advanced artificial synapses with solid state electrochemical cells and will contribute to the development of smart-terminal networking systems.

Moisture effects on the electrochemical reaction and resistance switching at Ag/molybdenum oxide interfaces.

An important potential application of solid state electrochemical reactions is in redox-based resistive switching memory devices. Based on the fundamental switching mechanisms, the memory has been classified into two modes, electrochemical metallization memory (ECM) and valence change memory (VCM). In this work, we have investigated a solid state electrochemical cell with a simple Ag/MoO3-x/fluorine-doped tin oxide (FTO) sandwich structure, which shows a normal ECM switching mode after an electroforming process. While in the lower voltage sweep range, the switching behavior changes to VCM-like mode with the opposite switching polarity to the ECM mode. By current-voltage measurements under different ambient atmospheres and X-ray photoemission spectroscopy analysis, electrochemical anodic passivation of the Ag electrode and valence change of molybdenum ions during resistance switching have been demonstrated. The crucial role of moisture adsorption in the switching mode transition has been clarified based on the Pourbaix diagram for the Ag-H2O system for the first time. These results provide a fundamental insight into the resistance switching mechanism model in solid state electrochemical cells.

Synthesis and characterization of bisoxazolines- and pybox-copper(II) complexes and their application in the coupling of α-carbonyls with functionalized amines.

Binuclear complexes [{(DMOX)CuCl}2(µ-Cl)2] (1), mononuclear complexes [(DMOX)CuBr2] (2) (DMOX = 4,5-dihydro-2-(4,5-dihydro-4,4-dimethyloxazol-2-yl)-4,4-dimethyloxazole) and the pybox Cu(II) complex [(Dm-Pybox)CuBr2] (3) (Dm-Pybox = 2,6-bis[4',4'-dimethyloxazolin-2'-yl]pyridine) were obtained by reactions of CuX2 (X = Cl, Br) with DMOX and Dm-Pybox ligands, respectively. The molecular structures of 1, 2 and 3 have been determined by single-crystal X-ray diffraction analyses. The complexes 2 and 3 are efficient in catalyzing α-amination of ketones and esters through α-bromo carbonyl intermediate. The procedures are environmentally benign methods using molecular oxygen as an oxidant with water as the only byproduct.

Evidence and evolution of magnetic polaron in HgCr2Se4 investigated by electron spin resonance.

The evidence and evolution of magnetic polarons (MPs) in HgCr2Se4 have been studied by electron spin resonance (ESR), magnetism and conductivity measurements in a temperature range of 5-300 K. A single paramagnetic resonance line is observed in the high-temperature range while multiple resonance lines appear in the low-temperature range. As temperature decreases, the peak-to-peak linewidth ΔH pp shows a minimum at T min ≈ 210 K, with the activation energy fitted by small polaron hopping model consistent with the bottleneck mechanism, providing an evidence for existence of small MPs above T min. The analysis of the temperature dependence of ΔH pp, double integrated intensity I, and g factor of ESR signals, combined with the temperature dependence of magnetization and conductivity, reveals an evolution process from small MPs at zone I (T > T min) to correlated MPs at zone II (T c < T * ⩽ T ⩽ T min) in the paramagnetic regime. Three critical temperatures, T min (≈210 K), T th (≈175 K), and T * (≈121 K), which determine the evolution characteristics of MPs, are distinguished. The magnetic correlation length ξ of Cr3+-Se2--Cr3+ should account for the evolution of MPs.

Field- and temperature-induced evolution of the magnetocaloric effect in Ba0.3Sr1.7Co2Fe12O22 single crystals with heliconical magnetism.

The magnetocaloric effect (MCE) associated with the spin transitions of alternating longitudinal conical (ALC)-mixed conical (MC) and MC-ferrimagnetic (FIM) states in a Ba0.3Sr1.7Co2Fe12O22 single crystal has been investigated. For magnetic field directions applied along either the [120] or [001] directions, the crystal is found to exhibit the conventional and inverse MCE near the ALC-MC (T(N1) = 235 K) and MC-FIM (T(N2) = 348 K) states, respectively. The dependence of the magnetic entropy on the magnetic field also exhibits such sign change behaviors in the MCE, which is attributed to the magnetic field induced gradual collapse of heliconical magnetic order.