排序方式: 共有54条查询结果,搜索用时 468 毫秒
21.
Woods PA Morrill LC Bragg RA Smith AD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(39):11060-11067
Screening of a range of chiral isothioureas and acyl donors to promote the asymmetric C-acylation of silyl ketene acetals indicates that C(2)-aryl-dihydropyrimidobenzothiazole-derived isothioureas and propionic anhydride give optimal reactivity and enantioselectivity in this process. Under optimised conditions 3-acyl-3-aryl or 3-acyl-3-alkylfuranones are prepared in good yields and moderate to excellent enantioselectivities (up to 98% ee; ee=enantiomeric excess). 相似文献
22.
Joannesse C Johnston CP Morrill LC Woods PA Kieffer M Nigst TA Mayr H Lebl T Philp D Bragg RA Smith AD 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(8):2398-2408
The structural motif within a series of tetrahydropyrimidine-based isothioureas necessary for generating high asymmetric induction in the asymmetric Steglich rearrangement of oxazolyl carbonates is fully explored, with crossover and dynamic (19)F?NMR experiments used to develop a mechanistic understanding of this transformation. 相似文献
23.
In this paper the relation betweenEP--matrices andE
k
P--matrices over an arbitrary filedF is studied. Further, conditions for the product ofE
k
P--matrices to be anE
k
P--matrix and for the reverse order law to hold for the polynomial Moore-Penrose inverse of the product ofE
k
P--matrices are determined 相似文献
24.
When hydroboration of 1-octene is carried out in the presence of catalytic amounts of rhodium trichloride followed by the usual oxidation (hydrogen peroxide in aqueous alkali), only minor proportions of 1-octanol (2.4%) are formed accompanied by very significant amounts of 2- (17.4%), 3- (36.9%), and 4-octanol (43.3%). These product compositions are obtained in good overall yield when the borane-THF complex is slowly added to a stirred solution of 1-octene in THF solvent containing the rhodium trichloride. Isomerization of 1-octene to 2-, 3-, and 4-octene in the presence of rhodium trichloride alone is far too slow to account for the foregoing results. The mechanism likely involves multiple and reversible addition/elimination of a Rh-activated B-H species across the double bonds. 相似文献
25.
V. ARÁMBULA-VILLAZANA M. SOLACHE-RÍOS M. T. OLGUÍN 《Journal of inclusion phenomena and macrocyclic chemistry》2006,55(3-4):237-245
Many factors may affect the heavy metals sorption on natural zeolites among them the temperature, for this reason in this paper the cadmium retention behavior on Mexican zeolitic rich tuff as a function of temperature is considered. The kinetic and the isotherms were determined at 303, 318, and 333 K, the remaining cadmium in the solution samples was analyzed by atomic absorption spectrometry. The pseudo-second order rate constant, k, as well as the apparent diffusion coefficients were calculated from the cadmium uptake by the zeolitic rock as a function of the contact time and temperature, the highest amounts were found for the experiments done at 333 K. The maximum cadmium adsorption capacity by the zeolitic material was 12.2 mg Cd2+/g at 318 K corresponding to 20% of the effective ion exchange capacity of the Chihuahua zeolitic rock. In order to explain the cadmium sorption behavior different kinetics and isotherm models were considered. 相似文献
26.
Two reaction strategies are developed to promote the highly selective 1,3-isomerization of a variety of allylic alcohols using O3ReOSiPh3 as a catalyst. The first strategy utilizes substrates whose 1,3-regioisomer contains a conjugated alkene, which relies on thermodynamics to obtain high selectivity. The second strategy employs N,O-bis(trimethylsilyl)acetamide as an additive to selectively and irreversibly remove the product from the reaction equilibrium and works well for the isomerization of tertiary allylic alcohols into primary allylic alcohols containing trisubstituted alkene components. High stereoselectivity is also observed in the 1,3-isomerization of enantioenriched allylic alcohols. 相似文献
27.
Dr. Alexander R. Nödling Dr. Katarzyna Świderek Dr. Raquel Castillo Jonathan W. Hall Dr. Antonio Angelastro Dr. Louis C. Morrill Dr. Yi Jin Dr. Yu‐Hsuan Tsai Prof. Vicent Moliner Dr. Louis Y. P. Luk 《Angewandte Chemie (International ed. in English)》2018,57(38):12478-12482
There has been growing interest in performing organocatalysis within a supramolecular system as a means of controlling reaction reactivity and stereoselectivity. Here, a protein is used as a host for iminium catalysis. A pyrrolidine moiety is covalently linked to biotin and introduced to the protein host streptavidin for organocatalytic activity. Whereas in traditional systems stereoselectivity is largely controlled by the substituents added to the organocatalyst, enantiomeric enrichment by the reported supramolecular system is completely controlled by the host. Also, the yield of the model reaction increases over 10‐fold when streptavidin is included. A 1.1 Å crystal structure of the protein–catalyst complex and molecular simulations of a key intermediate reveal the chiral scaffold surrounding the organocatalytic reaction site. This work illustrates that proteins can be an excellent supramolecular host for driving stereoselective secondary amine organocatalysis. 相似文献
28.
29.
MK Hossain-Ibrahim K Rezajooi JK MacNally MRJ Mason AR Lieberman PN Anderson 《BMC neuroscience》2006,7(1):8-21
Background
Inflammation around cell bodies of primary sensory neurons and retinal ganglion cells enhances expression of neuronal growth-associated genes and stimulates axonal regeneration. We have asked if inflammation would have similar effects on corticospinal neurons, which normally show little response to spinal cord injury. Lipopolysaccharide (LPS) was applied onto the pial surface of the motor cortex of adult rats with or without concomitant injury of the corticospinal tract at C4. Inflammation around corticospinal tract cell bodies in the motor cortex was assessed by immunohistochemistry for OX42 (a microglia and macrophage marker). Expression of growth-associated genes c-jun, ATF3, SCG10 and GAP-43 was investigated by immunohistochemistry or in situ hybridisation. 相似文献30.
Dias JR Pascal RA Morrill J Holder AJ Gao H Barnes C 《Journal of the American Chemical Society》2002,124(17):4647-4652
X-ray crystallographic determinations and AM1 calculations have defined the solid-state and gas-phase structures of cyclotri(deoxycholate) and cyclotetra(24-norcholate). The latter cyclotetramer is one of the largest open macrocycles ever subjected to crystallography. 相似文献