排序方式: 共有27条查询结果,搜索用时 15 毫秒
1.
Mitsunori Honda Yuichi Yamamoto Hideki Tsuchida Masahito Segi Tadashi Nakajima 《Tetrahedron letters》2005,46(38):6465-6468
Treatment of cyclopropylsilylmethanols derived from cyclopropyl silyl ketones with acid catalyst gives the corresponding silyl-substituted homoallyl derivatives in high yields with good stereoselectivity, independent of the substituents on the cyclopropyl ring. Cyclopropylsilylmethanols having a n-, s-butyl or phenyl group on the carbinyl carbon react to afford the E-homoallyl derivatives selectively. On the other hand, the reaction of cyclopropylsilylmethanols having a tert-butyl group gives Z-isomers exclusively. The following protiodesilylation of the resulting homoallyl derivatives proceeds with retention of configuration. 相似文献
2.
Extremely Photostable Electron-Deficient Phthalocyanines that Generate High Levels of Singlet Oxygen
Prof. Dr. Taniyuki Furuyama Yusuke Miyaji Kazuya Maeda Prof. Dr. Hajime Maeda Prof. Dr. Masahito Segi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2019,25(7):1678-1682
A robust lead-mediated synthetic procedure for the generation of phthalocyanines substituted with electron-withdrawing groups has been developed. The free-base phthalocyanine and various metal complexes were prepared without discernible degradation of the peripheral electron-withdrawing substituents. Upon irradiation with red light, some of the thus-obtained metal complexes generated high levels of singlet oxygen. In particular, a palladium complex exhibited attractive photostability upon exposure to singlet oxygen as a bleaching agent. The photostability of such complexes that may manifest concomitantly to the generation of high levels of singlet oxygen was attributed to the presence of the electron-withdrawing groups, which results in energetically low-lying highest occupied molecular orbitals. 相似文献
3.
Yoshino Katsurayama Prof. Yasuhiro Ikabata Prof. Hajime Maeda Prof. Masahito Segi Prof. Hiromi Nakai Prof. Taniyuki Furuyama 《Chemistry (Weinheim an der Bergstrasse, Germany)》2022,28(2):e202103223
The high penetration of near-infrared (NIR) light makes it effective for use in selective reactions under light-shielded conditions, such as in sealed reactors and deep tissues. Herein, we report the development of phthalocyanine catalysts directly activated by NIR light to transform small organic molecules. The desired photocatalytic properties were achieved in the phthalocyanines by introducing the appropriate peripheral substituents and central metal. These phthalocyanine photocatalysts promote cross-dehydrogenative-coupling (CDC) under irradiation with 810 nm NIR light. The choice of solvent is important, and a mixture of a reaction-accelerating (pyridine) and -decelerating (methanol) solvents was particularly effective. Moreover, we demonstrate photoreactions under visible-light-shielded conditions through the transmission of NIR light. A combined experimental and computational mechanistic analysis revealed that this NIR reaction does not involve a photoredox-type mechanism with electron transfer, but instead a singlet-oxygen-mediated mechanism with energy transfer. 相似文献
4.
Masahito Segi Hiroaki Yamamoto Takeyoshi Hori Tadashi Nakajima 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):599-602
Selenoaldehydes and selenoketones, generated by thermal retro-Diels-Alder reaction of their cycloadducts with cyclopentadiene, reacted with oxygen-functionalized conjugated dienes such as 1-acetoxy-1,3-butadiene, Danishefsky's diene, and 1,4-diacetoxy-1,3-butadiene to give the corresponding cycloadducts in good yields regioselectively. 相似文献
5.
Hajime Maeda Kazuhiro Tanaka Mona Aratani Masahito Segi 《Photochemistry and photobiology》2019,95(3):762-772
Substances containing ethynylpyrenes linked to either one or four benzocrown ethers were synthesized, and their absorption and fluorescence spectroscopic responses to metal ions were assessed. Addition of metal perchlorates to solutions of these substances promotes short wavelength shifts in their absorption and fluorescence maxima and increases in their fluorescence intensities. The magnitudes of the fluorescence intensity increases are dependent on the ring size and number of the crown ether and the nature of the metal cation. Association constants for complex formation were calculated using fluorescence intensity versus concentration data. Analysis using Job's plots showed that the substances containing one benzocrown ether moiety form 1:1 complexes with metal ions. Results of experiments employing repeated addition and removal of Mg(ClO4)2 demonstrate that the ON‐OFF fluorescence response can be repeated at least three times. Results of molecular orbital calculations show that complexation with metal ions lowers the energies of both the π and π* levels of the ethynylpyrene moiety and that in some cases the vacant orbital on the metal becomes the LUMO of the complex. An explanation of the spectroscopic changes promoted by metal ions is proposed in terms of electrostatic repulsion and structural regulation. 相似文献
6.
Taisei Ueda Naoyoshi Yatsuzuka Shin‐Ichi Nagai Kumiko Okada Emi Takeichi Hiromi Segi Jinsaku Sakakibara 《Journal of heterocyclic chemistry》2001,38(1):141-145
Oxidation of 7,8‐diaminotheophylline (1) with lead tetraacetate in refluxing toluene gave a mixture of 3‐amino‐5,7‐dimethylpyrimido[4,5‐e][1,2,4]triazine‐6,8‐dione ( 2 ) and 6‐cyanoimino‐5‐diazo‐1,3‐dimethylpyrimidine‐2,4‐dione ( 4 ). The latter was transformed to 2 by the reaction with 1‐propanethiol in quantitative yield. The reaction of 4 with methanol, ethanol and 1‐propanol in the presence of rhodium ( II ) acetate gave 5‐alkoxy‐6‐(2‐alkyl‐3‐isoureido)‐1,3‐dimethylpyrimidine‐2,4‐diones ( 7a‐c ). A similar reaction of 4 with alkylamines such as n‐propylamine, n‐butylamine, isobutylamine and n‐hexylamine gave a mixture of 7‐alkyl‐8‐aminotheophyllines ( 8a‐d ) and (5‐alkylamino‐1,3‐dimethyl‐2,4‐dioxopyrimidin‐6‐yl)cyanamides ( 9a‐d ). 相似文献
7.
Taniyuki Furuyama Daichi Tamura Hajime Maeda Masahito Segi 《Tetrahedron letters》2018,59(30):2913-2916
In this study, indolo-naphthyridine-6,13-diones (5a–d) with four different peripheral substituents were prepared via bay-annulation reactions of indigo. The resulting compounds (5a–d) exhibited fluorescence in the red to near-IR region, while the parent indigo molecule showed no fluorescence. Although the peripheral substituents were oriented to the exterior of the π-conjugated system, the electronic structure affected the absorption and fluorescence spectra. Moreover, calculated molecular orbitals and absorption spectra successfully reproduced the experimental absorption spectra and cyclic voltammograms. 相似文献
8.
Mitsunori Honda Yusuke Taniguchi Tomohiro Hayashi Ko-Ki Kunimoto Masahito Segi Takahiro Yamaguchi 《Tetrahedron letters》2017,58(48):4554-4558
The synthesis of a novel class of 3-silyl substituted thiophenes possessing perfluoroalkyl groups on the silicon atom was investigated. The treatment of 3-bromothiophene with n-butyllithium followed by the reaction with halosilanes proceeded to afford the corresponding 3-silyl substituted thiophenes 1 in good yields. The chemical polymerization of the resulting 1 did not work well. However, the electropolymerization of 3-silylthiophenes 1a and 1b provided the corresponding polymers 5a and 5b with head-to-tail regioregularity. The cyclic voltammogram of the resulting polymers 5a and 5b indicated both n- and p-doping properties. 相似文献
9.
Masahito Segi Aojia Zhou Mitsunori Honda 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):1045-1049
Abstract The [4, 2] cycloadducts of selenoaldehydes and anthracene regenerate selenoaldehydes in situ quantitatively under neutral conditions via thermal retro Diels–Alder reaction. The reactions of selenoaldehydes generated by this method with 2-silyloxy-1,3-butadiene, 2-methoxyfuran, and 5-ethoxyoxazoles are described. 相似文献
10.
Reaction behavior of cyclopropylmethyl cations derived 1-phenylselenocyclopropylmethanols with acids
Mitsunori Honda Toshiaki Nishizawa Yuko Nishii Shuhei Fujinami Masahito Segi 《Tetrahedron》2009,65(45):9403-5418
The 1-phenylselenocyclopropylmethyl cations are generated by the reaction of the corresponding cyclopropylmethanols 1 with TsOH. The reaction in methanol proceeds to afford the homoallylic ethers 2, ring-enlargement products 3, 4, and ring opening products 5 depending upon the kind of substituent on the cyclopropane ring or the α-carbon. On the other hand, in the case of the absence of methanol as nucleophile, 4H-selenochromene derivative 7 is obtained exclusively. The oxidative elimination of the phenylselenyl group in the resulting phenylselenohomoallylic compounds 2 furnishes functionalized allene derivatives and alkyne derivatives. 相似文献