Roles of sigmatropic migration of a benzoyl group and intermolecular hydrogen bonding between a tropone carbonyl and an NH group on the mesomorphic properties of 2-(4-alkoxybenzoyloxy)-5-alkylaminotropones and 5-alkoxy-2-(4-alkylaminobenzoyloxy)tropo

The mesomorphic properties of 2-(4-alkoxybenzoyloxy)-5-alkylaminotropones and 5-alkoxy-2-(4-alkylaminobenzoyloxy)tropones are discussed on the basis of results obtained by X-ray crystallographic and X-ray diffraction studies, as well as temperature-dependent FTIR spectral measurements. The X-ray crystallographic analysis of 2-(4-dodecylaminobenzoyloxy)-5-tetradecyloxytropone (2f) indicated that it formed a head-to-tail dimer through an intermolecular hydrogen bond between the NH and the tropone carbonyl group. The X-ray diffraction study of compound 2f suggested that the molecules formed interdigitated bilayer smectic C phases with a tilt angle of as much as c. 40° to a layer plane. The corresponding benzenoids, however, were non-mesomorphic, with higher melting points than the troponoids. In the troponoids, sigmatropic migration of the benzoyl group weakened the intermolecular hydrogen bonding and assisted the occurrence of mesomorphic properties.     

A Bacterial Chitinase Acts as Catalyst for Synthesis of the N‐Linked Oligosaccharide Core Trisaccharide by Employing a Sugar Oxazoline Substrate

A chitinolytic enzyme, chitinase A1 from Bacillus circulans WL‐12, was found to catalyze a glycosyl‐transferring reaction to form the N‐linked oligosaccharide core structure, Man(β1‐4)‐GlcNAc(β1‐4)‐GlcNAc, by employing Man(β1‐4)‐GlcNAc‐oxazoline as glycosyl donor. When the reaction was carried out in the presence of 20 v/v% acetone, the trisaccharide was obtained in 32% yield. It has been shown for the first time that a chitinase behaves like an endo‐β‐N‐acetylglucosaminidase in spite of low structural similarity between them.     

Reaktivit?t von Isopren gegen den Li-Di?thylamidDiathylamin-Komplex

Ohne Zusammenfassung     

Studies on the syntheses of heterocyclic compounds—DCXCIII: A total synthesis of atheroline by photolysis

Atheroline (3) an oxoaporphine alkaloid, has been synthesised by photolysis of 8 bromo 1-(3-hydroxy-4-methoxybenzoyl)-6,7-dimethoxyisoquinoline (13) in the presence of sodium hydroxide.     

An environmentally benign and practical synthesis of sugar orthoesters promoted by potassium fluoride

An extremely practical method for synthesis of sugar orthoesters has been developed without using any organic amines or heavy metals as additives. Various sugar orthoesters were prepared in good yields by the reaction of an acylated glycosyl bromide and an alcohol in the presence of potassium fluoride.     

Enhanced photocatalytic activity of α-methylstyrene oligomerization through effective metal-to-ligand charge-transfer localization on the bridging ligand

A series of Pd complexes containing a visible-light harvesting moiety with various combination of substituents (R, X) were synthesized. The variation of the substituents resulted in significant change in the electrochemical and photophysical properties of the complexes. Additionally, photocatalytic activity drastically increased through the introduction of an electron-donating group on R and an electron-withdrawing group on X, respectively. The molecular orbital analysis based on density functional theory (DFT) calculation suggested that the enhancement of the catalytic activity is due to the effective Metal-to-Ligand Charge-Transfer (MLCT) localization on the bridging ligand.     

Photochromic metal complexes: photoregulation of both the nonlinear optical and luminescent properties

A series of dithienylethene (DTE)-containing 2,2'-bipyridine ligands and their zinc(II) diacetate, zinc(II) dichloro, rhenium(I) tricarbonyl bromo, and ruthenium(II) bis(bipyridine) complexes have been designed and synthesized, and their photochromic, photophysical, and quadratic nonlinear optical properties have been studied. Upon UV irradiation at 350 nm, the ligands and complexes undergo ring closure of the DTE units, with a good to excellent photocyclization yield. In the case of the Re(I) and Ru(II) complexes, the photocyclization of the DTE units can also be triggered using visible light, upon excitation into the metal-to-ligand charge-transfer (MLCT) bands at 400 and 490 nm, respectively. Molecular quadratic nonlinear optical (NLO) responses of the complexes have been determined by using either the electrical field induced second harmonic generation (EFISH) or harmonic light scattering (HLS) technique at 1910 nm. These studies reveal a large increase of the second-order NLO activity after UV irradiation and subsequent formation of the ring-closed isomers. This efficient enhancement clearly reflects the delocalization of the π-electron system and the formation of strong push-pull chromophores in the closed forms. The combination of the photochromic DTE-based bipyridine ligand with luminescent Re(I) and Ru(II) fragments also allows the photoregulation of the emission, leading to an efficient quenching of the ligand-based 77 K luminescence and demonstrating that the photocontrol of two optical properties, linear and nonlinear, could be achieved by using the same photochromic ligand.     

Reactions of 3-isopropyl-, 3-isopropenyl-, and 3-acetyltropolone methyl ethers with guanidines. Synthesis of 9H-cyclohepta[d]pyrimidin-9-ones and cycloheptimidazoles

3-Isopropyl- and 3-isopropenyltropolone methyl ethers reacted with guanidine, 1-methylguanidine, and 1,1-dimethylguanidine to afford the corresponding 4-isopropyl- and 4-isopropenylcycloheptimidazoles 4a-f , respectively. The reactions of 3-acetyl-2-methoxytropones 2c-e with guanidines afforded 4-methyl-9H-cyclohepta[d]pyrimidin-9-ones 8a-i , while the reactions of 7-acetyl-2-methoxytropones 3c,d produced 4-acetylcycloheptimidazoles 4g-1 . From these reactions, several minor products were also isolated.