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91.
Hydroxylamine derivatives of (S)-prolinol have been generated using a Cope elimination. These undergo reverse-Cope elimination onto a pendant double bond to give morpholine N-oxides containing three contiguous chiral centres. 相似文献
92.
Alan R. Katritzky Amir S. Afridi Wojciech Kuzmierkiewicz 《Helvetica chimica acta》1991,74(8):1931-1935
tert-Alkyl sulfides, with an α-(1H-benzotriazol-1-yl) group 6 and 13 , are readily prepared from N-[(aryl-thio)methyl]-1H-benzotriazoles 3 and N-( 11 ), respectively, by reaction with BuLi and then with the appropriate electrophile. The tert-alkyl sulfides 6 and 13 are smoothly converted by BF3. OEt2 into vinyl sulfides 5, 7 or 12 , respectively, in satisfactory yields. 相似文献
93.
Alan M. Bond Roger J. OHalloran Ivica Ruzic Donald E. Smith 《Journal of Electroanalytical Chemistry》1978,90(3):381-388
Rate laws presented to date for analysis of a.c. cyclic voltammetric data have invoked the so-called “slow scan limit approximation” which requires that ΔEω ? v, where Δ E and ω are the applied a.c. potential amplitude and angular frequency, respectively, and v is the d.c. potential scan rate. To provide a more useful guideline for the experimentalist than this qualitative condition, a pure digital simulation approach has been used to compute the a.c. cyclic time domain waveform for a reversible process under small amplitude conditions. The a.c. content of this waveform is extracted by the digital FFT alogirthm. Results of this study are presented here. Among the conclusions reached are more quantitative limitations for the slow scan limit rate laws describing the fundamental and second harmonic responses (approximately 128 a.c. cycles/d.c. cyclic sweep and 512 a.c. cycles/d.c. cyclic sweep, respectively) and an interesting prediction that the latter limitations can be relaxed further by a current waveform subtraction strategy, to as low as about 16 a.c. cycles/d.c. cyclic sweep for the fundamental and second harmonics. The cycles/sweep values assume one triangular wave potential scan of ±200 mV is encompassed. 相似文献
94.
We introduce a new Monte Carlo algorithm for the self-avoiding walk (SAW), and show that it is particularly efficient in the critical region (long chains). We also introduce new and more efficient statistical techniques. We employ these methods to extract numerical estimates for the critical parameters of the SAW on the square lattice. We find=2.63820 ± 0.00004 ± 0.00030=1.352 ± 0.006 ± 0.025v=0.7590 ± 0.0062 ± 0.0042 where the first error bar represents systematic error due to corrections to scaling (subjective 95% confidence limits) and the second bar represents statistical error (classical 95% confidence limits). These results are based on SAWs of average length 166, using 340 hours CPU time on a CDC Cyber 170–730. We compare our results to previous work and indicate some directions for future research. 相似文献
95.
Wei ZL Sakamuri S Petukhov PA George C Lewin NE Blumberg PM Kozikowski AP 《Organic letters》2002,4(13):2169-2172
[structures: see text] Both (2S,5R,6R)- and (2S,5R,6S)-6-hydroxy-8-(1-decynyl)benzolactam-V8 were designed and synthesized as PKC modulators. Biological assays reveal the (6R)-ligand to be 20-fold more potent than its (6S)-counterpart in binding to PKC alpha. 相似文献
96.
Koteswara Rao Y Vijaya Bhaskar Reddy M Venkata Rao C Gunasekar D Blond A Caux C Bodo B 《Chemical & pharmaceutical bulletin》2002,50(9):1271-1272
Two new 5-deoxyflavones, 7,8-dimethoxy-3',4'-methylenedioxyflavone (1) and 7,2',4'-trimethoxyflavone (2) together with a known flavone, 7,4'-dimethoxy-3'-hydroxyflavone (3) were isolated from the rootbark of Albizia odoratissima. The structures of these new compounds were elucidated by electrospray ionization mass spectrometry (ESI-MS) and 1D and 2D-NMR spectral studies including (1)H-(1)H correlation spectroscopy (COSY), heteronuclear single quantum coherence (HSQC), heteronuclear multiple bond connectivity (HMBC) and nuclear Overhauser enhancement spectroscopy (NOESY). 相似文献
97.
Alan W. Duff Peter B. Hitchcock Michael F. Lappert Richard G. Taylor John A. Segal 《Journal of organometallic chemistry》1985,293(3):271-283
n-Heptane-soluble “di-butylmagnesium” (I) (a commercially available material, prepared by addition of LiBus to MgBunCl, and subsequent addition of ca. 5% MgOct2n) has been found to be a useful starting material for obtaining numerous organic magnesium compounds. This is illustrated by its reaction with a number of protic compounds HA to give in good yields Mg(C5H5)2, Mg(C5H4Me)2, or the new compounds MgA2: IV (A = C5H4SiMe3), V [A = C5H3(SiMe3)2], VII (A = OC6H2Bu2t-2,6-Me-4), and X [A2 = N(SiMe3)C6H4N(SiMe3)-o(OEt2)]. The value of such compounds MgA2 as mild ligand transfer reagents is illustrated by the synthesis of Zr(C5H3X2)Cl3 (X = H or SiMe3). Compound X was isolated from OEt2 solution as the crystalline dimer with two o-(SiMe3)C6H4(SiMe3) ligands bridging two magnesium atoms and a terminal OEt2 ligand completing a distorted tetrahedral environment around each Mg. Some key parameters are: MgNt 1.997(7), MgNb 2.083(8), MgO 2.041(7) Å; OMgNt 112.1(3), OMgNb 119.7(3), and NtMgNb 118.5(3)°. 相似文献
98.
Rockwood AL 《The Journal of chemical physics》2005,122(8):87103; discussion 87104
The entropy of the electron gas used by Llano and Eriksson (LE) in the definition they used for an absolute half-cell potential (AHCP) is indeterminate. This AHCP is therefore not based on a thermodynamically well-defined process and cannot easily be extended to other thermodynamic functions such as entropy. An alternative approach to the AHCP avoids these difficulties. The present comment also corrects statements and concepts presented by LE about the temperature coefficient of the Fermi level and surface charge of the electrolyte solution. 相似文献
99.
Armstrong A Ahmed G Dominguez-Fernandez B Hayter BR Wailes JS 《The Journal of organic chemistry》2002,67(24):8610-8617
Several alpha-substituted N-carbethoxytropinones have been evaluated as catalysts for asymmetric epoxidation of alkenes with Oxone, via a dioxirane intermediate. alpha-Fluoro-N-carbethoxytropinone (2) has been studied in detail and is an efficient catalyst which does not suffer from Baeyer-Villiger decomposition and can be used in relatively low loadings. This ketone was prepared in enantiomerically pure form using chiral base desymmetrization of N-carbethoxytropinone. Asymmetric epoxidation catalyzed by 2 affords epoxides with up to 83% ee. Among other derivatives tested, the alpha-acetoxy derivative 7 affords the highest enantioselectivities. 相似文献
100.
White-Morris RL Stender M Tinti DS Balch AL Rios D Attar S 《Inorganic chemistry》2003,42(10):3237-3244
The preparation and X-ray crystal structures of (CyNC)Au(I)CN, (n-BuNC)Au(I)CN, and (i-PrNC)Au(I)CN.0.5CH(2)Cl(2) are reported and compared with those of (MeNC)Au(I)CN and (t-BuNC)Au(I)CN, which were previously described. These linear molecules are all organized through aurophilic interactions into three structural classes: simple chains ((CyNC)Au(I)CN and (t-BuNC)Au(I)CN), side-by-side chains in which two strands make Au...Au contact with each other ((n-BuNC)Au(I)CN), and nets in which multiple aurophilic interactions produce layers of gold(I) centers ((i-PrNC)Au(I)CN and (MeNC)Au(I)CN). All of these five solids dissolve to produce colorless, nonluminescent solutions with similar UV/vis spectra. However, each of the solids displays a unique luminescence with emission maxima occurring in the range 371-430 nm. 相似文献