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81.
Kinoshita H Osamura T Mizuno K Kinoshita S Iwamura T Watanabe S Kataoka T Muraoka O Tanabe G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2006,12(14):3896-3904
Reactions between chiral 3-cinnamoyl-4-methyl-5-phenyl-1,3-oxazolidine-2-thiones and aromatic aldehydes in the presence of BF3Et2O diastereoselectively produced tricyclic compounds incorporating a bridgehead carbon bound to four heteroatoms in high yields. Four stereocenters were induced during the reaction. The tricyclic products were transformed into propane-1,3-diols bearing three consecutive stereocenters by acid hydrolysis, S-methylation, and reductive removal of the chiral auxiliary. 相似文献
82.
Warō Nakanishi Satoru Murata Yoshitsugu Ikeda Tadashi Sugawara Yuzo Kawada Hiizu Iwamura 《Tetrahedron letters》1981,22(42):4241-4244
The reaction of 2-methylselenobenzoic acid with 1,1′-carbonyldiimidazole followed by addition of t-butyl hydroperoxide gave cyclic selenuranes and , suggesting the intramolecular insertion of the neighboring selenium atom into the OO bond of t-butyl 2-methylselenoperoxybenzoate. In the reaction of 2-phenylselenobenzoyl chloride with t-butyl hydroperoxide, cyclic selenurane and the oxide were obtained. 相似文献
83.
84.
85.
Michiko Iwamura Morimatsu Katoh Hiizu Iwamura 《Magnetic resonance in chemistry : MRC》1980,14(5):392-397
The temperature-dependent 1H NMR spectra have been measured for the bisadducts 2a and 3 of 1-cyano-1-methylethyl radicals with α-phenyl-N-benzylnitrone [N-(benzylidene)benzylamine N-oxide] and nitrosobenzene, respectively. A free energy of activation of ΔG≠ = 62.8 ~ 64.4 kJ mol?1 (15.0 ~ 15.4 kcal/mol) at 24 ~ 45 °C has been obtained for 2a by applying the Eyring equation to the rate constants at the coalescence points of the methyl signals. The line shapes due to four methyl signals exchanging between two sites of equal population have been simulated by the theoretical calculation to give an activation enthalpy of 52.3 kJ mol?1 (12.5 kcal/mol) and the corresponding entropy of ?39.3 J K?1 mol?1 for 3. As the inversion barriers at pyramidal nitrogens of hydroxylamine derivatives should be lowered in N-phenyl derivatives because of conjugation, the rate process which is responsible for the observed temperature dependent NMR spectra can be assigned to restricted rotation around one of the skeletal C? N? O? C bonds. The relevance of the results to the conformations of nitroxides derived from the spin trapping method using α-phenyl-N-t-butylnitrone [N-(benzylidene)-t-butylamine N-oxide] and nitroso spin traps is discussed. 相似文献
86.
Shigeto Okada Senichi Yamashita Toshiaki Furuta Michiko Iwamura 《Photochemistry and photobiology》1995,61(5):431-434
A highly fluorescent 1-pyrenylmethyloxycarbonyl amino acid (Pmoc-amino acid) is obtained in moderate yield by the reaction of (1-pyrenylmethyl)-4-nitrophenylcarbonate with an amino acid in the presence of sodium carbonate. The condensation of Pmoc-amino acid with an amino acid gives Pmoc-peptide in the presence of 1-ethyl-3-(3-dimethylaminepropyl)carbodiimide and 1-hydroxyben-zotriazole. The amino acid is recovered from an H2O-dioxane (2:3) solution of Pmoc-amino acid by irradiation through a Pyrex filter with a medium pressure Hg lamp or at 340 nm. Although the quantum yield of the photolysis is rather low (ca 0.01), the photolysis proceeds fast and efficiently due to the large absorption coefficient of Pmoc-amino acid at around 340 nm. Thus, the use of Pmoc-amino acid as a “caged” amino acid is promising. 相似文献
87.
Watanabe Si Mori E Nagai H Iwamura T Iwama T Kataoka T 《The Journal of organic chemistry》2000,65(26):8893-8898
The treatment of alkynylselenonium salt and various thiophenol derivatives with a catalytic amount of triethylamine gave beta-arylthioalkenylselenonium salts in good yields. The alkenylselenonium salts thus prepared reacted with nucleophiles such as acetylides, thiolates, and alkoxides to produce (Z)-beta-arylthio-alpha-functionalized ethenes in high yields. The vinylselenonium salts bearing a hydroxy group on a beta-side chain caused intramolecular cyclization upon treatment with sodium hydride to produce medium-membered heterocyclic compounds containing sulfur and oxygen atoms. The reactions giving (Z)-beta-arylthio-alpha-functionalized ethenes would proceed via the formation of selenurane intermediates followed by the ligand coupling reaction. 相似文献
88.
Akira Sekiguchi Wataru Ando Tadashi Sugawara Hiizu Iwamura Michael T.H. Liu 《Tetrahedron letters》1982,23(40):4095-4098
Carbenes generated from 10-diazo-9,9-dimethyl-9,10-dihydro-9-silaanthracene and 10-diazo-9,9-dimethyl-9,10-dihydroanthracene gave hydrogen abstraction products by the triplet nature of these carbenes. The triplet dihydrosilaanthracenylidene was shown by the electron spin resonance study. 相似文献
89.
Yu Takano Yasutaka Kitagawa Taku Onishi Yasunori Yoshioka Kizashi Yamaguchi Noboru Koga Hiizu Iwamura 《Journal of the American Chemical Society》2002,124(3):450-461
Bis(hexafluoroacetylacetonato(hfac))manganese(II) coordinated with di(4-pyridyl)phenylcarbene, Mn(II)(hfac)(2)[di(4-pyridyl)phenylcarbene] (1a) and its copper analogue Cu(II)(hfac)(2)[di(4-pyridyl)phenylcarbene] (2a) have attracted great interest from the viewpoint of photoinduced magnetism. The complexes 1a and 2a are regarded as the new d-pi-p conjugated systems containing transition metal ion and carbene as spin sources. The magnetic measurements demonstrated antiferromagnetic and ferromagnetic effective exchange interactions for 1a and 2a, respectively. Here, we have performed UHF and UHF plus DFT hybrid calculations (UB3LYP) to elucidate the nature of the through-bond effective exchange interaction between Mn(II) (or Cu(II)) ion and triplet carbene sites in 1a (or 2a) and their model complexes. The natural orbital analysis of the UHF and UB3LYP solutions and CASCI calculations for the simplest models of 1a and 2a are performed to elucidate relative contributions of spin polarization (SP) and spin delocalization (SD) (or superexchange (SE)) interactions for determination of the sign of J(ab) values. Mn(II) carbene complex 1a shows an antiferromagnetic interaction because of the pi-type antiferromagnetic SE effect and the pi-type SP effect, while the positive J(ab) value for Cu(II) carbene complex 2a can be explained by the fact that ferromagnetic SE and SP interactions due to orbital orthogonality are more effective than the sigma-type antiferromagnetic SE interaction. The ligand coordination effects of both 4-pyridylcarbene and hfac play crucial roles for determination of the J(ab) values, but the ligand coordination effect of hfac is more important for the active control of charge or spin density distributions than that of 4-pyridylcarbene. The spin alignment mechanisms of 1a and 2a are indeed consistent with SE plus SP rule, which is confirmed with the shape and symmetry of natural orbitals, together with charge and spin density distributions. 相似文献
90.
Kataoka T Kinoshita S Kinoshita H Fujita M Iwamura T Watanabe S 《Chemical communications (Cambridge, England)》2001,(19):1958-1959
The tandem Michael-aldol reaction of 1-[2-(methylsulfanyl)-phenyl]prop-2-en-1-one (1) or the seleno congener 4 with p-nitrobenzaldehyde in the presence of BF3.Et2O gave the Baylis-Hillman adduct 2 or 5 and onium salt 3 or 6, respectively, and selenochromanone 7 from 4. 相似文献