排序方式: 共有33条查询结果,搜索用时 15 毫秒
11.
The partial reduction of electron-deficient pyridines is described herein. Mono- and disubstituted pyridines can be transformed into functionalized dihydropyridines using either Birch reduction conditions or sodium/naphthalene in THF. The compounds formed by these high-yielding reductive alkylation protocols have potential as synthetic intermediates, and we have shown that bicyclo compounds containing 6,5, 6,6, and 6,7 ring systems can be prepared in one step via a base-promoted cylization. 相似文献
12.
A new beam deflection and collimation technique is described which utilizes transverse gain variations in laser amplifiers. This method may be used to achieve beam mixing or optical isolation between the stages of an amplifier chain. Results with a CO2 amplifier are decribed. 相似文献
13.
14.
15.
16.
Pors K Loadman PM Shnyder SD Sutherland M Sheldrake HM Guino M Kiakos K Hartley JA Searcey M Patterson LH 《Chemical communications (Cambridge, England)》2011,47(44):12062-12064
The identification of an agent that is selectively activated by a cytochrome P450 (CYP) has the potential for tissue specific dose intensification as a means of significantly improving its therapeutic value. Towards this goal, we disclose evidence for the pathway of activation of a duocarmycin analogue, ICT2700, which targets CYP1A1 for biological activity. 相似文献
17.
Petra DG Reek JN Handgraaf JW Meijer EJ Dierkes P Kamer PC Brussee J Schoemaker HE van Leeuwen PW 《Chemistry (Weinheim an der Bergstrasse, Germany)》2000,6(15):2818-2829
The enantioselective outcome of transfer hydrogenation reactions that are catalysed by ruthenium(II) amino alcohol complexes was studied by means of a systematically varied series of ligands. It was found that both the substituent at the 1-position in the 2-amino-1-alcohol ligand and the substituent at the amine functionality influence the enantioselectivity of the reaction to a large extent: enantioselectivities (ee values) of up to 95% were obtained for the reduction of acetophenone. The catalytic cycle of ruthenium(II) amino alcohol catalysed transfer hydrogenation was examined at the density functional theory level. The formation of a hydrogen bond between the carbonyl functionality of the substrate and the amine proton of the ligand, as well as the formation of an intramolecular H...H bond and a planar H-Ru-N-H moiety are crucially important for the reaction mechanism. The enantioselective outcome of the reaction can be illustrated with the aid of molecular modelling by the visualisation of the steric interactions between the ketone and the ligand backbone in the ruthenium(II) catalysts. 相似文献
18.
Poolman HR Boersma DJ Harvey M Higinbotham DW Passchier I Six E Alarcon R van Amersfoort PW Bauer TS Boer Rookhuizen H van Den Brand JF van Buuren LD Bulten HJ Ent R Ferro-Luzzi M Geurts DG Heimberg P de Jager CW Klimin P Koop I Kroes F van Der Laan J Luijckx G Lysenko A Militsyn B Nesterenko I 《Physical review letters》2000,84(17):3855-3858
We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space. 相似文献
19.
Derek R. Boyd David Clarke Marcel C. Cleij John T. G Hamilton Gary N. Sheldrake 《Monatshefte für Chemie / Chemical Monthly》2000,131(6):673-685
Summary. The bacterium Pseudomonas putida ML 2 was used in the oxidative biodegradation of the acyclic dienes isoprene, trans-piperylene, cis-piperylene, and 1,3-butadiene. Regioselective dioxygenase-catalyzed dihydroxylation of alkenes yielded vicinal diols in the
preferred sequence monosubstituted > cis-disubstituted > gem-disubstituted > trans-disubstituted. The isolated diol metabolites had an excess of the R configuration (9–97%ee), and further diol oxidation was controlled by addition of propylene glycol as an inhibitor. Stereoselectivity using the
ML2 strain resulted from both enzymatic asymmetric alkene dihydroxylation and kinetic resolution of diols. Enantioselective
oxidation of the allylic secondary alcohol group of R configuration yielded the corresponding unsaturated ketoalcohol; the residual diol was recovered with a large excess (≥ 93%ee) of the S configuration. In addition to the enzymatic diene oxidation steps yielding unsaturated diols and ketoalcohols, evidence was
also found of enzymatic alkene hydrogenation to yield saturated ketoalcohols and diols.
Received December 20, 1999. Accepted (revised) February 7, 2000 相似文献
20.