The reaction of spiro[indoline‐naphthopyrans] with nitrogen oxides. Not a case of biradical double trapping

The reactions of six differently substituted photochromic spiro[indoline‐naphtopyrans] with ·NO or ·NO₂ under normal daylight conditions have been investigated by means of EPR spectroscopy along with those of three structurally related spiro[indoline‐benzopyrans]. The spectra due to cyclic oxynitroxides originating from double trapping of biradicals by ·NO were observed with the three latter derivatives, this finding being in agreement with previous results. Similar signals were also observed with the six former compounds, but in this case they were responsible for just a minor component of the spectra, the main spectral signals being due to hitherto unreported paramagnetic species that on the basis of their spectral parameters are identified as iminoxy radicals. DFT calculations at the B3LYP/6‐31G* level carried out on a variety of radicals support this assignment. Copyright © 2009 John Wiley & Sons, Ltd.     

(S,S)-2,3-Dihydroxy-2,3-dihydrobenzoic acid: microbial access with engineered cells of Escherichia coli and application as starting material in natural-product synthesis

Cyclohexadiene-trans-5,6-diols such as (S,S)-2,3-dihydroxy-2,3-dihydrobenzoic acid (2,3-trans-CHD) have been shown to be of importance as chiral starting materials for the syntheses of bioactive substances, especially for the syntheses of carbasugars. By using methods of metabolic-pathway engineering, the Escherichia coli genes entB and entC, which encode isochorismatase and isochorismate synthase, were cloned and over-expressed in E. coli strains with a deficiency of entA, which encodes 2,3-dihydroxybenzoate synthase. A 30-fold increase in the corresponding EntB/EntC enzyme activities affects the accumulation of 2,3-trans-CHD in the cultivation medium. Although the strains did not contain deletions in chorismate-utilising pathways towards aromatic amino acids, neither chorismate nor any other metabolic intermediates were found as by-products. Fermentation of these strains in a 30 L pH-controlled stirred tank reactor showed that 2,3-trans-CHD could be obtained in concentrations of up to 4.6 g L(-1). This demonstrates that post-chorismate metabolites are accessible on a preparative scale by using techniques of metabolic-pathway engineering. Isolation and separation from fermentation salts could be performed economically in one step through anion-exchange chromatography or, alternatively, by reactive extraction. Starting from 2,3-trans-CHD as an example, we established short syntheses towards new carbasugar derivatives.     

Selective complex formation of some chromogenic calix[4]arene derivatives detected by Fourier transform infrared spectroscopy 2. Solid experiments

Two chromogenic calix[4]arene derivatives having identical coordination sphere (consisting of ester groups) but different chromogenic units (pyridinium type and dinitro-phenyl type) were the subject of structural studies with sodium(I) and thallium(I) ions in solid state, both as bulk and surface complexes. Their diffuse reflectance infrared Fourier transform (DRIFTS) spectra were recorded and the characteristic changes of the vibrational spectra due to complex formation were analysed based on curve fitting.     

l,3-Dipolar cycloaddition of unsatu rated ferrocene derivatives with carbonitrileN-oxides

3,5-Disubstituted isoxazolines and isoxazoles have been synthesized using 1,3-dipolar cycloaddition of ferrocene derivatives FcCH=CH₂, FcCOCH=CH₂ and FcCCH with aliphatic and aromatic carbonitrileTV-oxides.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 139–142, January, 1994.     

A charge-stabilized Jahn-Teller Distortion of the Mixed Valence System NaBa2Cu3O6

The crystal structure of NaBa₂M₃O₆ contains an unusual hexagonal prism composed of linked MO₄ squares. This unit is distorted in the M = Cu compound but undistorted in the M = Ni material. Electronic structure calculations show an orbital degeneracy and electronic stabilization on distortion of the hexagonal prism at the electron count appropriate for the Cu compound. The preferred distortion is determined by considering how the nature of both the occupied and unoccupied metal d orbitals are consistent with the metal oxidation states set by the stoichiometry. The results provide added insights into the nature of mixed valence compounds. The synthesis of Na₂BaM₃O₆ is encouraged.     

Preparation of Novel Materials for Catalysts Utilizing Metal-Containing Silsesquioxanes

Recent progress of the preparation of novel materials for catalysts utilizing metal-containing silsesquioxanes are reviewed in the following categories: (i) activities of vanadium or titanium-containing silsesquioxanes as homogeneous catalysts for oxidative reactions, (ii) preparation of immobilized or polymeric catalysts, and (iii) preparation of porous oxide catalysts utilizing metal-containing silsesquioxanes. The present authors found that the liquid phase photo-oxidation of cyclohexane in the presence of a vanadium-containing silsesquioxane as a homogeneous catalyst selectively afforded cyclohexanol and cyclohexanone in high yields. Facile synthetic methods for group 4 metal-containing silsesquioxanes with functionalized silyl (or germyl) groups are presented. Remarkably, titanocene(IV)-containing silsesquioxanes have been synthesized for the first time. The presence of alkenylsilyl substituents shows a promotional effect on the epoxidation of cycloalkenes, which was found to be more significant for titanium-bridged silsesquioxanes. By utilizing these silsesquioxanes, polymeric, starburst-like, and dendritic silsesquioxanes were prepared as well as novel caged or macrocyclic molecules with organic–inorganic hybrid structures. The controlled calcination of these metal-containing silsesquioxanes at around 823 K produces porous oxides with high BET surface areas of 300–520 m²g⁻¹ and uniformly-controlled micropores of 0.5–0.6 nm diameter. The oxides are found to include a well-dispersed metallic oxide species. From group 13 elements-containing silsesquioxanes Br?nsted acidic oxides are produced. Among them, aluminum-containing oxides show excellent activities for the cracking of cumene even at low temperature, 523 K, in spite of their amorphous nature.