[4+1] Cycloaddition of N-acylimine derivatives with isocyanides: efficient synthesis of 5-aminooxazoles and 5-aminothiazoles

[4+1] Cycloaddition reaction between isocyanides and N-acylimine derivatives generated from N-acyl N,O-acetals acting as isocyanophiles has been developed. These reactions proceeded smoothly and cleanly to afford the corresponding 5-aminooxazoles in high yields. This reaction was extended to the syntheses of 5-aminothiazoles by using N-thioacyl N,O-acetals. A wide range of N-acyl N,O-acetals, N-thioacyl N,O-acetals, and isocyanides were found to be applicable to this reaction.     

Role of Re Species and Acid Cocatalyst on Ir‐ReOx/SiO2 in the C–O Hydrogenolysis of Biomass‐Derived Substrates

The catalytic performance of ReO_x‐modified Ir metal catalyst in the hydrogenolysis of C–O bonds is strongly dependent on the choice of solvent. The acidic property of the Re species becomes obvious in the alkane solvent, and the hydrogenolysis reaction proceeds mainly by acid‐catalyzed dehydration and the subsequent metal‐catalyzed hydrogenation. The acidic property of the Re species is weakened in water; however, the hydrogenolysis reaction proceeds in water via a direct mechanism involving S_N2‐like attack of a hydride species at the interface between Ir and ReO_x on the adsorbed Re alkoxide species. This mechanism enabled the selective dissociation of the C–O bond neighboring the CH₂OH group.     

Copper‐Catalyzed CH Bond Direct Chalcogenation of Aromatic Compounds Leading to Diaryl Sulfides,Selenides, and Diselenides by Using Elemental Sulfur and Selenium as Chalcogen Sources Under Oxidative Conditions

The reactions of aromatic compounds and elemental chalcogens catalyzed by a copper salt with molecular oxygen as an oxidant were carried out. The reaction of 3‐substituted imidazo[1,5‐a]pyridines and elemental sulfur in the presence of CuTC (copper(I) thiophenecarboxylate) gave the corresponding bisimidazopyridyl sulfides in good to quantitative yields. The reaction proceeded even under aerobic oxidation conditions. The use of a polar solvent was crucial for the reaction, and DMSO (dimethyl sulfoxide) in particular stimulated the reaction. The reaction could be applied to common aromatic compounds, such as N‐methyl indole and dialkyl anilines. The reaction of indole proceeded at the nucleophilic C3 position rather than at the acidic C2 position. In addition, the reaction of dialkyl anilines proceeded with an ortho, para orientation. The reactions of imidazopyridines and elemental selenium under similar conditions gave the corresponding bisimidazopyridyl diselenides along with bisimidazopyridyl monoselenides. The resulting diselenides were readily converted to the corresponding monoselenides with unreacted imidazopyridines under the same conditions. The reaction could be applied to the copolymerization of bifunctional bisimidazopyridines and elemental sulfur to give oligomeric copolymers in quantitative yield.     

Solubility of Anthraquinone Derivatives in Supercritical Carbon Dioxide: New Correlations

Solubility of several anthraquinone derivatives in supercritical carbon dioxide was readily available in the literature, but correcting ability of the existing models was poor. Therefore, in this work, two new models have been developed for better correlation based on solid–liquid phase equilibria. The new model has five adjustable parameters correlating the solubility isotherms as a function of temperature. The accuracy of the proposed models was evaluated by correlating 25 binary systems. The proposed models observed provide the best overall correlations. The overall deviation between the experimental and the correlated results was less than 11.46% in averaged absolute relative deviation (AARD). Moreover, exiting solubility models were also evaluated for all the compounds for the comparison purpose.     

Dual Catalysis with Copper and Rhenium for Trifluoromethylation of Propargylic Alcohols: Efficient Synthesis of α‐Trifluoromethylated Enones

Trifluoromethylation of propargylic alcohols to provide (Z)‐α‐trifluoromethylated enones and β‐unsubstituted α‐trifluoromethylated enones proceeded with high yield and selectivity in the presence of CuI/Re₂O₇. The Z isomer was formed under kinetic control, though it is less stable than the E isomer in terms of steric repulsion.     

Molecularly Designed Nanoparticles by Dispersion of Self‐Assembled Organosiloxane‐Based Mesophases

The design of siloxane‐based nanoparticles is important for many applications. Here we show a novel approach to form core–shell silica nanoparticles of a few nanometers in size through the principle of “dispersion of ordered mesostructures into single nanocomponents”. Self‐assembled siloxane–organic hybrids derived from amphiphilic alkyl‐oligosiloxanes were postsynthetically dispersed in organic solvent to yield uniform nanoparticles consisting of dense lipophilic shells and hydrophilic siloxane cores. In situ encapsulation of fluorescent dyes into the nanoparticles demonstrated their ability to function as nanocarriers.     

Preparation and properties of isotactic and syndiotactic poly(methyl methacrylate)s,uniform with respect to molecular weight

Highly isotactic (it-) and highly syndiotactic (st-) poly(methyl methacrylate)s (PMMAs) uniform with respect to molecular weight (stereoregular, uniform PMMAs) were isolated up to the 100mer from it- and st-PMMAs by supercritical fluid chromatography (SFC) and characterized by NMR and mass spectroscopies. Glass transition temperatures (Tg's) of the uniform it- and st-PMMAs were higher than those of the corresponding PMMAs with MWD and with similar molecular weight on average. The Tg values of the uniform it-and st-PMMAs series obeyed the relationship, Tg = Tg∞ - K/M, where M and Tg∞ denote molecular weight and Tg at infinite M, respectively. The reciprocal melting points (1/Tm) of uniform it-PMMA (degree of polymerization, DP = 28–44), obtained from methanol solutions by evaporating the solvent, increased linearly with increasing 1/DP. Extrapolation of the linear relation to 1/DP = 0 gave the Tm of it-PMMA with infinite DP; Tm∞ = 171.1°C. Thermal degradation behavior was studied by thermogravimetry and by SFC analysis of degradation products. In gel-permeation chromatography (GPC) measurements, the it-50mer eluted faster than the st-50mer. Calibration curves for it- and st-PMMAs could be obtained using series of the uniform PMMAs. The instrumental spreading factor determined using it-25mer, it-50mer, st-25mer and st-50mer for our GPC chromatograph was 0.070 ml when the volume of the sample solution was 0.003ml. GPC analysis of a mixture of the it- and st-50mers in tetrahydrofuran indicated formation of a stereocomplex in the solution, and was found quite useful to elucidate the minimum sequence length required for complex formation.     

Short Radiative Lifetime and Non-Triplet Sensitization in Near-Infrared-Luminescent Yb(III) Complex with Tripodal Schiff Base

We prepared Ln(III) (Ln=Eu, Gd, and Yb) complexes with a tripodal Schiff base, tris[2-(5-methylsalicylideneimino)ethyl]amine (H₃L) and studied their photophysical properties. Upon ligand excitation, YbL showed Yb(III)-centered luminescence in the near-infrared region. While the overall quantum yield (0.60(1)%) of YbL in acetonitrile was moderate among the reported values for Yb(III) complexes, its radiative lifetime (0.33(2) ms) was significantly shorter than those reported previously. We propose that the ligand-to-metal charge-transfer (LMCT) state mediated the sensitization in YbL. The emission and excitation spectra of EuL indicated the participation of the LMCT state in the sensitization. The radiative lifetime (0.84(7) ms) for EuL in the solid state was rather short compared to those of reported Eu(III) complexes. Our results show that the Yb(III) complex with the Schiff base ligand has two features: the short radiative lifetime and the non-triplet sensitization path.