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111.
A tandem asymmetric conjugate addition-cyclopropanation was developed, in which a cyclic or linear enone was converted to a TMS-protected 3-substituted-cyclopropanol in an efficient one-pot reaction. These compounds were then selectively cleaved to yield alpha-methyl-beta-alkyl ketones, alpha-methylene-enones, or chain extended gamma-alkyl-enones. This methodology was applied to the formal total synthesis of (-)-(S,S)-clavukerin A and (+)-(R,S)-isoclavukerin. 相似文献
112.
Dupont J Fonseca GS Umpierre AP Fichtner PF Teixeira SR 《Journal of the American Chemical Society》2002,124(16):4228-4229
1-n-Butyl-3-methylimidazolium hexafluorophosphate room-temperature ionic liquid is not only suitable as a medium for the preparation and stabilization of iridium nanoparticles but also ideal for the generation of recyclable biphasic catalytic systems for hydrogenation reactions. Thus, Ir(0) nanoparticles with a mean diameter of 2 nm have been prepared by reduction of Ir(I) dissolved in the ionic liquid with H2. This catalytic solution can be reused several times for the biphasic hydrogenation of olefins under mild reaction conditions. 相似文献
113.
Bernard Coupet Hervé Gaussier Alexandre Sukhov 《Proceedings of the American Mathematical Society》1999,127(11):3191-3200
We study rigidity and regularity properties of CR maps between smooth convex hypersurfaces of finite type in
114.
Alexandre Froda 《Annali di Matematica Pura ed Applicata》1978,44(1):185-199
Résumé L’on définit, pour ρ>0 donné, des familles de para-voisinages J(J) (§ 1) des pointsJ de l’espace euclidienE
(n),continus par rapport àJ. On étudie certaines propriétés à distance, ?.-à-d. qui rattachent les valeurs de f(P) reélle, borneé, enJ et sur J(J). L’ensemble desJ est alors relativement dense enE
(n) (§ 2). Résultats pareils en renon?ant à la continuité (§ 3). 相似文献
115.
The effect of silica aerosils on the kinetics of the first-order nematic-isotropic (NI) phase transition is phenomenologically described in the framework of the time-dependent Landau-Ginzburg equation. A steady-state solution to the equation is presented such that the NI interface may propagate with a solitary-like wave profile under constant quenching. The results provide a plausible basis for the interpretation of the dynamical effects of quenched disorder in the liquid-crystal systems, caused by randomly interconnected porous media, such as aerosils. In the low silica aerosil ρs ( ≤0.1 g/cm^3) regime, the calculated values of the interface velocity v(T,ρs), the interface thickness κ(T,ρs), and the critical radius of a spherical nucleus of new nematic phase in a bulk isotropic environment, composed of polar molecules, such as 4-n-octyl- 4′- cyanobiphenyl and 4-n-heptyl- 4′- cyanobiphenyl shows that the effect of silica aerosils on the kinetics is reflected in a shifting of the set of temperature-dependent curves to lower temperature values.-1 相似文献
116.
117.
[reaction: see text] The addition of nucleophiles to 3-substituted pyridinium salts prepared from N-methylbenzamide and various pyridines has been investigated. Good to excellent regioselectivities favoring the 2,3-disubstituted 1,2-dihydropyridines were observed. The resulting 1,2-dihydropyridines led to the corresponding 2,3-disubstituted pyridines upon treatment with Mn(OAc)3/NaIO4. This methodology was also successfully applied to the enantioselective syntheses of (-)-L-733,061 and (-)-CP-99,994, two members of a new class of highly potent, nonpeptide, Substance P antagonists. 相似文献
118.
The (C,F)-construction from a previous paper of the first authoris applied to produce a number of funny rank one infinite measurepreserving actions of discrete countable Abelian groups G withunusual multiple recurrence properties. In particular,the following are constructed for each p N{}:
- a p-recurrent actionT=(Tg)gG such that (if p) no one transformationTg is (p+1)-recurrentfor every element g of infinite order;
- an action T=(Tg)gGsuch that for every finite sequence g1,...,grGwithout torsionthe transformation Tg1x...x Tgr is ergodic,p-recurrent but(if p) not (p+1)-recurrent;
- a p-polynomially recurrent (C,F)-transformationwhich (if p)is not (p+1)-recurrent.
119.
We use multispeckle diffusive wave spectroscopy to probe the micron-scale dynamics of a water-saturated granular pile submitted to discrete gentle taps. The typical time scale between plastic events is found to increase dramatically with the number of applied taps. Furthermore, this microscopic dynamics weakly depends on the solid fraction of the sample. This process is largely analogous to the aging phenomenon observed in thermal glassy systems. We propose a heuristic model where this slowing-down mechanism is associated with a slow evolution of the distribution of the contact forces between particles. This model accounts for the main features of the observed dynamics. 相似文献
120.
We present a theoretical analysis and experimental demonstration of the combined effects of polarization attraction and Raman amplification in isotropic optical fibers. The polarization attraction process is based on four-wave mixing interaction of counterpropagating pump and signal waves. We show that this technique can be used for the design of a highly efficient nonlinear system that permits the simultaneous processing of repolarization and amplification of light waves in dielectric media. 相似文献