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排序方式: 共有380条查询结果,搜索用时 15 毫秒
31.
A new ketone synthesis by palladium-catalyzed cross-coupling reactions of esters with organoboron compounds 总被引:1,自引:0,他引:1
[reaction: see text] The palladium-catalyzed coupling reaction of 2-pyridyl esters with organoboron compounds is described. The reaction is compatible with various functional groups and proceeds under mild reaction conditions. The coordination of the nitrogen atom to Pd is a key step for efficient reaction. 相似文献
32.
The coefficient of normal restitution in an oblique impact is theoretically studied. Using a two-dimensional lattice model for an elastic disk and an elastic wall, we demonstrate that the coefficient of normal restitution can exceed unity and has a peak against the incident angle in our simulation. We also explain this behavior based upon a phenomenological theory. 相似文献
33.
(--)-Muricatacin, a potent cytotoxic (4R,5R)-5-hydroxyheptadecan-4-olide, has been synthesized through alpha-C--H hydroxyalkylation and alpha'-C--H oxidation of tetrahydrofuran. This study presents a novel method for C--H bond functionalization as a means for preparing gamma-(hydroxyalkyl)-gamma-butyrolactones. 相似文献
34.
35.
HX Zhang M Kato Y Sasaki T Ohba H Ito A Kobayashi HC Chang K Uosaki 《Dalton transactions (Cambridge, England : 2003)》2012,41(37):11497-11506
Dinuclear complexes [{Pt(trpy)}(2)(L)](PF(6))(2) (trpy = 2,2':6',2'-terpyridine, L = 2-octylthio-1,3,5-triazine-4,6-dithiolate ion (1), L = 2-octadecylthio-1,3,5-triazine-4,6-dithiolate ion (2), L = 2-di-n-butylamino-1,3,5-triazine-4,6-dithiolate ion (3)) and a trinuclear complex [{Pt(trpy)}(3)(L)](PF(6))(3) (L = 1,3,5-triazine-2,4,6-trithiolate ion (4)) have been synthesized and characterized. The single crystal X-ray analysis revealed that the two {Pt(trpy)}(2+) fragments in 1 and 3 adopt a syn-configuration. The PtPt distances are around 4.3 ?, suggesting no intramolecular PtPt interactions. Complexes 1-4 in acetonitrile show broad absorption bands at around 470 nm, assigned to mainly the ligand-to-ligand charge transfer ((1)LLCT) from triazine thiolates to trpy based on the comparison to the related complexes and the density functional theory (DFT) calculations. The red luminescence of 1-4 in acetonitrile is attributable to emission predominantly from (3)LLCT. Cyclic voltammograms of 1-3 exhibit four redox couples from -2.0 V to 0 V vs. Ag/AgCl. The two consecutive processes at around -0.70 V are assigned to the sequential reduction of two trpy ligands. This assignment was further supported by the observation of the anion radical of trpy in spectroelectrochemical experiments. The splitting of the redox potentials of two trpy ligands evidences the moderate electronic coupling interactions mediated by the triazine dithiolate bridges. Complex 2 formed a transparent red gel in CH(3)CN, whereas 4 produced a gel-like solid in the mixtures of CH(3)CN and other solvents. The interactions dominating the aggregative behaviours have been discussed based on the results of electronic absorption and emission spectroscopy. 相似文献
36.
Okuyama Y Nakano H Takahashi K Hongo H Kabuto C 《Chemical communications (Cambridge, England)》2003,(4):524-525
Easily prepared, chiral sulfideoxathiane ligands are described which give excellent enantioselectivity (up to 99% ee) in the Pd-catalyzed allylic alkylation of 1,3-diphenyl-2-propenyl acetate with a range of alkyl malonate nucleophiles. 相似文献
37.
Isiaka A. Owolabi U.V. Subba Reddy Madhu Chennapuram Chigusa Seki Yuko Okuyama Eunsang Kwon Koji Uwai Michio Tokiwa Mitsuhiro Takeshita Hiroto Nakano 《Tetrahedron》2018,74(36):4705-4711
A new type of amino amide organocatalysts was designed and synthesized from commercially available amino acids in easy steps. Their catalytic activities were examined in enantioselective crossed aldol reaction of various acyclic and cyclic ketones with aromatic aldehydes to afford the corresponding chiral anti-aldol adducts with good to excellent chemical yields, diastereoselectivities and enantioselectivities (up to 99%, up to syn:anti?=?1:99, up to 97% ee). 相似文献
38.
Hiroto Nagaoka Kaoru Kobayashi Toshiaki Okamura Yasuji Yamada 《Tetrahedron letters》1987,28(52):6641-6644
The sequential Michael reaction of (S)-4,5-di-O-isopropylidenepent-2- enoate
and
with lithium enolate
afforded diastereo- and enantioselectively bicyclo[2.2.2]octane
and
(or
), respectively. The adducts were efficiently converted into both enantiomeric keto aldehydes (−)-
and (+)-
. 相似文献
39.
Shengang Xu Hiroto Kudo Tadatomi Nishikubo Shinya Nakamura Shunichi Numata 《Journal of polymer science. Part A, Polymer chemistry》2010,48(9):1931-1942
The acetyl esterified calixarene (CA) derivatives were prepared from calix[4]resorcinarene (CRA), and p‐tert‐butylcalixarene (BCA[n], n = 4, 6, 8), respectively. Using these CA derivatives as curing agents, the thermal curing reactions of two multifunctional epoxy resins (jER 828, 186 g/equiv., and ESCN, 193.7 g/equiv.) were investigated. The temperatures of glass transition (Tg) and decomposition (T) were measured by DSC and TGA, respectively. Based on the yields, Tgs, and Tds of the thermal cured jER 828 epoxy resin with CRA‐E100, the curing conditions were optimized to be tetrabutylphosphonium bromide (TBPB) as catalyst in NMP at 160 °C for 15 h. Under this curing condition, the cured materials of jER 828 or ESCN using various CA derivatives as curing agents were prepared. Except for BCA4 derivatives, the yields of thermal curing reaction were higher than 90%. Tgs and Ts of the resultant cured materials were in the range of 113–248 °C and 363–404 °C, respectively. These results mean that the cured epoxy resins with excellent Tgs were successfully formed by using CA derivatives as curing agents. It was also found that the Tgs of cured epoxy resins were strongly affected by the degree of esterification of CA derivatives. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 1931–1942, 2010 相似文献
40.
In order to investigate thermal behaviors of the hydrogen species, H+ ion and H atom, adsorbed on the surface of planar graphite, the direct molecular orbital dynamics (MO) calculations at AM1 level are applied to the hydrogen terminated planar cluster models included by the species, C54H18·H+ and C54H18·H, respectively. This is the first trial to describe the thermal behaviors of these species in terms of MO dynamics. Both hydrogen species form the covalent bonds with the surface carbon atoms through the sp3 hybrid orbitals which inhibit their dissociation at high temperature up to 2000 K. It was found that the reduction of band gap is introduced by the adsorption of H+ ion. 相似文献