Functional‐Group‐Tolerant Catalytic Migratory Oxidative Coupling of Nitrones

A copper‐catalyzed migratory oxidative‐coupling reaction between nitrones and various ethers/amines exhibited high functional‐group tolerance. Even in aqueous media, the reaction proceeded efficiently. For practical use of this catalysis, a unique sequential Huisgen cycloaddition was demonstrated. Mechanistic investigations revealed that the reaction proceeded through oxidative catalytic activation of ethers/amines to afford iminium/oxonium intermediates by concurrent dual one‐electron abstractions by copper(II) and oxyl radicals.     

Structure prediction and aromaticity of acenes and phenylenes series. A combination method between asymmetric Kekulé structures

The combination method between asymmetric Kekulé structures (CMAK) was expanded to the structure prediction of a series of acenes and phenylenes. The structures predicted by the CMAK correspond to those calculated by the ab initio molecular orbital (MO) and B3LYP density functional methods. The CMAK can characterize the structures. The aromaticity for the whole ring and each ring in the treated compounds was estimated by the index of deviation from aromaticity (IDA). The estimated aromaticity corresponds fairly well to the characterization of the structure predicted by the CMAK. The predicted structures of linear acenes reveal the aromaticity of the central ring and also explain its reactivity. The side ring in [n]phenacene shows high aromaticity. The critical difference in the structure and aromaticity for the central six‐membered ring of the isomers benzo[1,2:4,5]dicyclobutene and benzo[1,2:5,6]dicyclobutene was explained. Copyright © 2012 John Wiley & Sons, Ltd.     

Mechanofluorochromism of carbazole-type D–π–A fluorescent dyes

We have newly designed and synthesized unsymmetrical carbazole-type D–π–A fluorescent dyes. The dyes show a bathochromic shift-type mechanofluorochromism (MFC): grinding of as-recrystallized dyes induces a bathochromic shift of fluorescent color and the fluorescent color is recovered by heating or exposure to solvent vapor. In order to clarify the MFC mechanism for the carbazole-type D–π–A fluorescent dyes, time-resolved fluorescence spectroscopy, X-ray powder diffractometry, single-crystal X-ray structural analysis, IR spectroscopy, and differential scanning calorimetry are performed before and after grinding of the solids. On the basis of experimental results and semi-empirical molecular orbital calculations (AM1 and INDO/S), we have revealed that the MFC is attributed to a reversible switching between crystalline and amorphous states with changes of intermolecular hydrogen bonding and π–π interaction.     

The direct catalytic asymmetric aldol reaction of α-substituted nitroacetates with aqueous formaldehyde under base-free neutral phase-transfer conditions

Enantioselective direct aldol reaction of α-substituted nitroacetates with aqueous formaldehyde for the synthesis of α-alkyl serines has been achieved under base-free neutral phase-transfer conditions with a bifunctional chiral phase-transfer catalyst.     

Synthesis and Aromaticity of Benzene-Fused Doubly N-Confused Porphyrins

A bicyclo[2.2.2]octadiene(BCOD)-fused bis(dipyrromethane) derivative was reacted with methylal in the presence of trifluoroacetic acid followed by oxidation with chloranil to give a doubly N-confused phlorin derivative, which did not undergo the retro-Diels–Alder reaction extruding an ethylene molecule on heating. In contrast, a 7-tert-butoxybicyclo[2.2.1]heptadiene(7-BuOBCHD)-fused bis(dipyrromethane) yielded benzene-ring-fused doubly N-confused porphyrins by following similar reaction sequences.     

Color change (yellow \documentclass{article}\pagestyle{empty}\begin{document}$\rightleftharpoons$\end{document} orange) of 4,6,7-tri(alkoxy-substituted aryl)-1,2,5-thiadiazolo[3,4-c]pyridines in the solid phase

Reversible color change of 4,6,7-tri(alkoxy-substituted phenyl)-1,2,5-thiadiazolo[3,4-c]pyridines 5 in the solid state was observed: on grinding, yellow crystals of 5 became an orange amorphous solid which, on heating or washing with an appropriate solvent, gave the original yellow crystals.     

T-matrix analysis of electromagnetic wave differaction from a Fourier grating

This paper is described for T-matrix analysis of the electromagnetic wave diffraction from a Fourier grating that the boundary value problem is treated by applying the extended boundary condition. The rigorous form of the expression of matrix elements is presented in the term of Bessel functions of the first kind. The error of power conservation versus the truncated number has been examined for mode number. Diffraction efficiencies versus groove depth and wavelength for a second or third harmonic wave of Fourier grating have been discussed. Numerical results are in good agreement with those obtained from other method and experimental values. Reasonable numerical results are presented for a groove depth per period of the Fourier grating less than 0.25.     

Deactivation of external acid sites of H-mordenite by silica-modification in the isopropylation of biphenyl

Although extensive isomerization of 4,4'-diisopropylbiphenyl (4,4'-DIPB) occurred at 300^oC over H-mordenite, high selectivity for 4,4'-DIPB among DIPB isomers was observed over silica-modified H-mordenite. This is due to the prevention of the isomerization of 4,4'-DIPB by the deactivation of external acid sites. This revised version was published online in June 2006 with corrections to the Cover Date.     

Michael addition of N-isobutylidene-t-butylamine to dimethyl methoxymethylenemalonate and a new synthesis of some fused pyrazole derivatives from the adduct

N-Isobutylidenemethylamine reacted with dimethyl methoxymethylenemalonate to afford the N-alkylation product 3a exclusively. Exchanging the N-substituent of the Schiff's base from methyl to t-butyl altered the course of the reaction, allowing Michael addition to take place predominantly. The Michael adduct 4c on reaction with hydrazinoalkanols 6a,b, 6c,d and 6e gave tetrahydropyrazolo[5,1-b]oxazoles 9a,b , tetrahydro-pyrazolo[5,1-b][1,3]oxazines 9c,d and hexahydropyrazolo[5,1-b][1,3]oxazepine 9e , respectively.