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151.
Armando Córdova 《Tetrahedron letters》2004,45(20):3949-3952
Enantioselective proline-catalyzed direct asymmetric cross-aldol reactions with aldehydes were performed in ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate media, which simplified product isolation and catalyst recycling, affording 3-hydroxy aldehydes in high yield with excellent stereoselectivity. In addition, the enhanced reactivity of the asymmetric cross-aldol reactions in ionic liquid allowed the catalyst loading to be lowered significantly. 相似文献
152.
Future contributions to Journal of Chemical Crystallography 相似文献
153.
Manuel Salmón Armando Cabrera Nieves Zavala Georgina Espinosa-Pérez Jorge Cárdenas Rubén Gaviño Raymundo Cruz 《Journal of chemical crystallography》1995,25(11):759-762
3,4,5-Trimethoxybenzyl alcohol was cyclooligomerized with a bentonite clay used as a catalyst. Results of the crystal structure analysis of the racemic (±) nonamethoxy[1,1,1]orthocyclophane trimer, C30H36O9, are described. The structure was determined by X-ray diffraction at 293 K and shown to belong to the triclinic space group P
. The compound possesses a distorted crown conformation with unusual C–H...O intermolecular interactions, and with a crystal packing not observed before in other related derivatives. The racemic mixture was also discriminated in its two enantiomeric isomers, using proton NMR and Eu(III) as a chiral shift reagent. 相似文献
154.
Dulce?Paloma?del J.?Gutiérrez-Hijar Fausto?Becerra J.?E.?Puig J.?Félix?Armando?Soltero-Martínez María?Belén?Sierra Pablo?C.?SchulzEmail author 《Colloid and polymer science》2004,283(1):74-83
The aggregation of two polymerisable surfactants dodecylethylmethacrylatedimethylammonium bromide (C12PS) and hexadecylethylmethacrylatedimethylammonium bromide (C16PS) was studied with a battery of methods. Both surfactants form premicelles at low concentration, and show a critical micelle concentration and a transition between spherical and rod-like micelles. The micelle ionization degree and the adsorption at the air/solution interface were also studied. Results are interpreted on the basis of the conformation of the polar head group. 相似文献
155.
Elimination of fluoride ions in water for human consumption using hydroxyapatite as an adsorbent 总被引:2,自引:0,他引:2
V. E. Badillo-Almaraz J. Armando Flores H. Arriola F. A. López L. Ruiz-Ramirez 《Journal of Radioanalytical and Nuclear Chemistry》2007,271(3):741-744
In this work, a synthetic hydroxyapatite, Bio-gel HTP, marketed by BIO-RAD®, has been studied in order to propose a method to remove the excess fluoride present in drinking water. The removal of fluoride ions by this adsorbent has been studied as a function of solution pH, and fluoride ion concentration. Experiments of fluoride ions sorption have been carried out with the use of 18F radiotracer in solutions of NaF at several concentrations with an ion selective electrode used for fluoride analysis. The adsorption isotherms show that the best fluoride adsorption on hydroxyapatite occurs at a pH range of 7.0–7.5. At this pH value the solid presents an important capacity of subtraction of fluoride, of around of 100 mmol/100 g. 相似文献
156.
Córdova A Notz W Zhong G Betancort JM Barbas CF 《Journal of the American Chemical Society》2002,124(9):1842-1843
The development of syntheses providing enantiomerically pure alpha-amino acids has intrigued generations of chemists and been the subject of intense research. This report describes a general approach to functionalized alpha-amino acids based on catalytic asymmetric synthesis. Proline catalyzed Mannich-type reactions of N-PMP-protected alpha-imino ethyl glyoxylate with a variety of unmodified ketones to provide functionalized alpha-amino acids in high yields with excellent regio-, diastereo-, and enantioselectivities. Study of seven examples yielded six with product ee values of > or = 99%. In reactions involving ketone donors where diastereoisomeric products could be formed, two adjacent stereogenic centers were created simultaneously upon carbon-carbon bond formation with complete syn-stereocontrol. Significantly, this methodology utilizes readily available and rather inexpensive starting materials, does not require any preactivation of substrates or metal ion assistance, and can be carried out on a gram scale under operationally simple reaction conditions. The keto-functionality present in the products provides a particularly attractive site for versatile modifications. This study compliments and extends our bioorganic approach to asymmetric synthesis to a versatile synthon class. Given that we have shown that a variety of optically active amino acids can be synthesized with proline catalysis, where an L-amino acid begets other L-amino acids, our results may stimulate thoughts concerning prebiotic syntheses of optically active amino acids based on this route. 相似文献
157.
Organocyanamides, Ntbd1;CNR(2) (R = Me or Et), react with trans-[Mo(N(2))(2)(dppe)(2)] (1, dppe = Ph(2)PCH(2)CH(2)PPh(2)), in THF, to give the first mixed molybdenum dinitrogen-cyanamide complexes trans-[Mo(N(2))(NCNR(2))(dppe)(2)] (R = Me 2a or Et 2b) which are selectively protonated at N(2) by HBF(4) to yield the hydrazide(2-) complexes trans-[Mo(NNH(2))(NCNR(2))(dppe)(2)][BF(4)](2) (R = Me, 3a, or Et, 3b). On treatment with Ag[BF(4)], oxidation and metal fluorination occur, and the ligating cyanamide undergoes an unprecedented beta-protonation at the unsaturated C atom to form trans-[MoF(NCHNR(2))(dppe)(2)][BF(4)](2) (R = Me, 4a, or Et, 4b) compounds which present the novel amidoazavinylidene (or amidomethyleneamide) ligands. Complexes 4 are also formed from the corresponding compounds 3, with liberation of ammonia and hydrazine. The crystal structure of 2b was determined by single-crystal X-ray diffraction analysis which indicates that the N atom of the amide group has a trigonal planar geometry. 相似文献
158.
N. S. Gnep M. L. Martin de Armando M. Guisnet 《Reaction Kinetics and Catalysis Letters》1980,13(3):183-189
Toluene transformation was investigated on a fluorided alumina and a protonic mordenite under hydrogen (0.8, 12 bar) and under nitrogen (12 bar). Hydrogen pressure considerably improves the catalytic stability of H-mordenite by inhibiting the formation of coke. Moreover, hydrogen eliminates part of the coke deposited by reaction under nitrogen, and regenerates the activity of the mordenite. On the contrary, hydrogen has no effect in the case of fluorided alumina. The particular behavior of the mordenite is attributed to its very strong acidity.
(0,8, 12 ) (12 ). -, . , , , . , - . .相似文献
159.
Nazario Martín Angeles Martínez-Grau Carlos Seoane Jos L. Marco Armando Albert Flix H. Cano 《Journal of heterocyclic chemistry》1996,33(1):27-31
The first asymmetric synthesis of 3-alkoxycarbonyl-2-amino-4-aryl-4H-naphtho[1,2-b]pyrans, by Michael addition of 1-naphthol to chirally modified arylidenecyanoacetates 6 and 7 , is described. Good yields and low diastereomeric excesses have been obtained in the 1,4-conjugate additions. The absolute stereochemistry at C-4 in major isomers of pyrans 8 and 9 has been assigned as 5 by X-ray analysis of major pyran 8 . 相似文献
160.
Summary The interconversion of carbyne, carbyne and hydride complexes derived from protonations oftrans-[M(CNMe)2(dppe)2](M = Mo or W) has been studied. The initial site of protonation is shown to be the isonitrile nitrogen and all protonations proceed through the common carbyne intermediatetrans-[M(CNHMe)(CNMe)(dppe)2]+. The CNHMe group in traps-[M(CNHMe)2(dppe)2]2+ is shown to be susceptible to electrophilic attack at N and nucleophilic attack at ligating C, the new complexestrans-[W(CNH2Me)(CNHMe)(dppe)2](BF4)3 andtrans-[Mo(CHNHMe)(CNHMe)(dppe)2]BF4 being formed, respectively. 相似文献