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Boesten WH Seerden JP de Lange B Dielemans HJ Elsenberg HL Kaptein B Moody HM Kellogg RM Broxterman QB 《Organic letters》2001,3(8):1121-1124
[reaction: see text]. Diastereoselective Strecker reactions based on (R)-phenylglycine amide as chiral auxiliary are reported. The Strecker reaction is accompanied by an in situ crystallization-induced asymmetric transformation, whereby one diastereomer selectively precipitates and can be isolated in 76-93% yield and dr > 99/1. The diastereomerically pure alpha-amino nitrile obtained from pivaldehyde (R1 = t-Bu, R2 = H) was converted in three steps to (S)-tert-leucine in 73% yield and >98% ee. 相似文献
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Fera A Dolbnya IP Grubel G Muller HG Ostrovskii BI Shalaginov AN de Jeu WH 《Physical review letters》2000,85(11):2316-2319
Coherent dynamic x-ray scattering has been used to study the thermally excited layer fluctuations in freely suspended smectic films of the compound 4O.8. Using 8-keV x rays and films with a thickness around 0.3 &mgr;m we resolve relaxation times down to a few &mgr;s. A combination of damped and oscillatory behavior is observed for the layer undulations, which can be attributed to inertial effects. These are due to the surface contribution to the free energy which cannot be disregarded for thin films. 相似文献
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van Eis MJ van Der Linde BS de Kanter FJ de Wolf WH Bickelhaupt F 《The Journal of organic chemistry》2000,65(14):4348-4354
In contrast to the terminal phosphinidene complex PhPW(CO)(5) (2), which adds to [5]metacyclophane (1) in a 1,4-fashion, dichlorocarbene preferentially adds in a 1,2-fashion to the formal "anti-Bredt" type double bond of the aromatic ring of 1 to afford the norcaradiene 11b, which immediately rearranges to the bridged cycloheptatriene 12b and further by a [1,5] sigmatropic chlorine migration to the isomeric 13b as the first observable product. More slowly, the latter isomerizes via a dissociative mechanism to give 15b. A computational study supports the notion that the [1,5] chlorine migration in the rearrangement 12b --> 13b, for which an activation barrier of 70.2 kJ mol(-)(1) was calculated, is essentially concerted with minor charge separation. In contrast, the analogous [1,5] chlorine migration in the flat model compound 7,7-dichlorocycloheptatriene (12a) displays features of a dissociative pathway. 相似文献
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Boesten JM Berkheij M Schoemaker HE Hiemstra H Duchateau AL 《Journal of chromatography. A》2006,1108(1):26-30
This paper describes the enantiomeric resolution of a series of unsaturated N-methyloxycarbonyl-alpha-H-alpha-amino acids (N-MOC-alpha-amino acids) on macrocyclic glycopeptide stationary phases by means of high-performance liquid chromatography (HPLC). Three types of glycopeptide phases, i.e. Chirobiotic T, V and R, were evaluated in both reversed-phase (RP) and polar ionic mode (PIM). The best results in terms of enantioselectivity and resolution were obtained on Chirobiotic R phase, with the PIM mobile phase giving the highest resolution per min. Investigation of the pH of the reversed-phase mobile phase in the pH range 4.1-5.9 showed little effect on enantioselectivity. The method was applied for monitoring the conversion and product enantiomeric excess of an enzymatic hydrolysis reaction using N-MOC-alpha-H-alpha-amino acid esters as substrate. 相似文献
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Ch. Berger W. Lackas F. Raupach W. Wagner G. Alexander J. Bürger L. Criegee H. C. Dehne R. Devenish G. Flügge G. Franke Ch. Gerke E. Hackmack P. Harms G. Horlitz Th. Kahl G. Knies E. Lehmann B. Neumann B. Stella R. L. Thompson U. Timm P. Waloschek G. G. Winter S. Wolff W. Zimmermann O. Achterberg V. Blobel L. Boesten H. Daumann A. F. Garfinkel H. Kapitza B. Koppitz W. Lührsen R. Maschuw H. Spitzer R. van Staa G. Wetjen A. Bäcker K. Derikum C. Grupen H. J. Meyer G. Zech H. J. Daum H. Meyer O. Meyer M. Rössler K. Wacker PLUTO Collaboration 《Zeitschrift fur Physik C Particles and Fields》1979,1(4):343-347
The electronic width Γ ee and the muonic branching ratioB μμ =Γ μμ /Γtot of the Γ(9.46) have been measured as Γ ee =(1.33±0.14) andB μμ=(2.2±2.0)%. From these values a lower limit of Γtot<23keV for the total width of the Γ(9.46) is obtained. 相似文献
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