Intramolecular photoreactions of 6-(ω-alkenyl)-4-methoxy-2-pyrones

6-(ω-Alkenyl)-2-pyrones 3a-c and 8a, b were prepared and the photochemical reactions were investigated. Photosensitized reactions of 3b, c gave intramolecular [2+2]-cycloadducts 11b, c as tricyclic lactones, site-and regio-specifically. They are not frontier-orbital-controlled adducts. On the other hand, 3a, 8a, b afforded cyclobutenecarboxylic acids, 10a, 14a, b , respectively. The end-ester group at the side-chain is thought not to be effective for the intramolecular phptoaddition.     

On the bromine variations in mouse lymphoma

Bromine and chlorine concentrations in some tissues (liver, spleen, thymus) of healthy mice (normal group) and lymphomatous mice (lymphoma group) were determined by neutron activation analysis. There were significant differences in the Br concentrations of the tissues between the normal and lymphomatous group, while the Cl concentrations were found relatively constant in all the tissues. As a result, the Br/Cl ratios in the tissues of the lymphomatous group were significantly higher than those of the normal group. It was difficult to conclude that Br was absorbed into the bodies of lymphomatous mice more easily than was Cl. It is suggested that Br excretion from the body is suppressed.     

Synthesis of 4,5-diaminopyrrolo[1,2-a]quinoline derivatives by annulation of N,N-dialkyl[2-(pyrrol-1-yl)benzylidene]ammonium salts in the presence of an isocyanide

A facile synthetic method for 4,5-diaminopyrrolo[1,2-a]quinoline derivatives has been developed. Treatment of 2-(pyrrol-1-yl)benzaldehydes with secondary amine hydrochloride/NaI/TMSCl/Et₃N in the presence of an isocyano compound leads to the formation of 4-alkyl(or aryl)amino-5-dialkylaminopyrrolo[1,2-a]quinolines.     

Hydrogen analysis in solid samples by utilizing He metastable atoms induced by TEA CO2 laser plasma in He gas at 1 atm

A TEA CO₂ laser (350 mJ–1.5 J, 10.6 μm, 200 ns, 10 Hz) was focused onto a metal sub-target under He as host gas at 1 atmospheric pressure with a small amount of impurity gas, such as water and ethanol vapors. It was found that the TEA CO₂ laser with the help of the metal sub-target is favorable for generating a strong, large volume helium gas breakdown plasma at 1 atmospheric pressure, in which the helium metastable-excited state was then produced overwhelmingly. While the metal sub-target itself was never ablated. The helium metastable-excited state produced after the strong helium gas breakdown plasma was considered to play an important role in exciting the atoms. This was confirmed by the specific characteristics of the detected H emission, namely the strong intensity with low background, narrow spectral width, and the long lifetime. This technique can be used for gas and solid samples analysis. For nonmetal solid analysis, a metal mesh was introduced in front of the nonmetal sample surface to help initiation of the helium gas breakdown plasma. For metal sample, analysis can be carried out by combining the TEA CO₂ laser and an Nd–YAG laser where the Nd–YAG laser is used to ablate the metal sample. The ablated atoms from the metal sample are then sent into the region of helium gas breakdown plasma induced by the TEA CO₂ laser to be excited through the helium metastable-excited state. This technique can be extended to the analysis of other elements, not limited only to hydrogen, such as halogens.     

Alternative copolymerization of aziridines and carbon monoxide by γ-ray irradiation

The copolymerization of carbon monoxide and aziridines such as ethylenimine and propylenimine was carried out by γ-ray irradiation. Aziridines and carbon monoxide were allowed to copolymerize under γ-ray irradiation from a Co⁶⁰ source and gave a crystalline solid copolymer. The yield of the copolymer increased with reaction temperature. The composition of copolymers obtained did not depend on the feed ratio of monomers and was found to be almost equimolar. The copolymer of ethylenimine and carbon monoxide melted at about 322–335°C. with decomposition and has an infrared spectrum identical with that of poly-β-alanine obtained by the hydrogen-migration polymerization of acrylamide. The hydrolyzed product of the ethylenimine–carbon monoxide copolymer was confirmed to be β-alanine by paper chromatography. These results lead to the conclusion that the copolymerization of aziridines and carbon monoxide took place alternatively by γ-ray irradiation, and produced crystalline poly-β-alanines.     

Cobaltporphyrin‐adsorbed carbon black: highly efficient electrocatalysts for oxygen reduction

meso‐Substituted cobalt porphyrins adsorbed on carbon black were prepared as catalysts for the electroreduction of O₂. The catalyst, which was prepared by using a homogenizer in mixing cobalt tetraethylporphyrin and carbon black, gave rise to electroreduction of O₂ at a remarkably positive potential (E_p = 0.45 V versus saturated calomel electrode (SCE)) and showed a high selectively for the four‐electron reduction (n = 3.8). Electrochemical study and extended X‐ray absorption fine structure (EXAFS) analysis revealed that the adsorbed face‐to‐face dimeric aggregates of cobalt porphyrin molecules were highly efficient catalysts for electroreduction of O₂. Copyright © 2005 John Wiley & Sons, Ltd.     

Photoinduced face-inversion of conjugated tetraene ligands on a Pd-Pd-Pd moiety

The linear sandwich tripalladium complexes [Pd3{Ar(CH=CH)4Ar}2[BArf]2 (Ar = Ph, p-t-Bu-C6H4, p-styryl-C6H4) undergo photoinduced isomerization involving face-inversion of the tetraene ligands. Irradiation of these complexes with visible light (>510 nm) resulted in rac (staggered sandwich) to meso (eclipsed sandwich) isomerization. The structures of rac and meso isomers are determined by X-ray crystallographic analyses.     

A new synthetic pathway of segmented tri-block copolyether

A new synthetic pathway of A–B–A tri-block copolyether which is composed of a hydrophilic poly(oxyethylene) unit as an A part and a hydrophobic poly(oxy-2-methyl-trimethylene) unit as a B part is proposed. Telechelic α-tosyl-ω-tosyloxypoly(oxy-2-methyl-trimethylene) derived from tosylation of poly(oxy-2-methyl-trimethylene glycol) (PMTG) was allowed to react with poly(ethylene glycol) (PEG) in the presence of sodium hydroxide. T_g of the resulting A–B–A tri-block copolyether (PEMG) (M?_n = 1600) was ?72°C and its specific gravity [D₄¹⁵] was 1.055.     

Singlet and triplet photocycloaddition reactions of 2-pyridones with propenoate and 2,4-pentadienotes,and the frontier molecular orbital analysis

Regioselective photocycloadditions of 2-pyridones ( 1 ) with 2,4-pentadienoates ( 3 ) were analysed and compared with the reactions with propenoate ( 2 ), and origins of the different regioselectivities were inferred from frontier molecular orbital properties by the use of PM3-CI method. Direct photoreactions of 1 with 3 being α,β,γ,δ-unsaturated carboxylates gave four types of regio-selective [2+2]cycloadducts, 3-β:4-α-4, 5, 3-δ:4-γ-6,7,5-δ: 6-γ-8, 9 and 5-δ:6-γ-[2+2]cycloadducts 10,11. Sensitized photoreactions of 1 with 3 did not occur, and fluorescence of 1 was weakly quenched by 3. Otherwise, main cycloadducts in the sensitized reactions of 1 with 2 have been obtained as 5-α:6-β-[2+2]cycloadducts, which were different from main 3-β:4-α-[2+2]cycloadducts of the direct reactions, and these site-and regio-selectivities were inferred from the different frontier molecular orbital coefficients at the. 3-and 6-positions of 1 for the triplet and singlet states. Formations of 4–7 were also interpreted by both effects of frontier orbital HSOMO-LUMO interactions and of the electrostatic interaction between 1 and 3. The other site-and regioselective adducts 8–11 were inferred to be formed by the electrostatic interactions similar to 2-pyridone photodimerization.