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41.
Ramakrishna P. Bhat 《Tetrahedron letters》2005,46(28):4801-4803
β-Acetylamino ketones have been obtained in a one-pot coupling of an aldehyde with an enolisable ketone, acetyl chloride and acetonitrile in the presence of zeolite Hβ as catalyst at room temperature (26-28 °C). The procedure has the advantages of mild workup, circumvention of high temperature and inert atmosphere. The catalyst was found to be recyclable. 相似文献
42.
The separation of chlorthalidone enantiomers in capillary electrochromatography on an achiral stationary phase when adding a chiral selector, hydroxypropyl-β-cyclodextrin, to the mobile phase, was optimised. The goal was to investigate the feasibility of modelling retention times and resolution when during the optimisation procedure regular replacement of columns is required due to their fragility. Therefore, it is essential that the packing procedure delivers reproducible columns. The optimisation of an existing chlorthalidone separation was chosen as case study. The influence of two factors, chiral selector concentration and organic modifier content, on the responses was modelled. The experiments performed prior to modelling were defined by a central composite design. Results on different columns, obtained under identical experimental conditions, were found comparable and thus modelling was possible in situations where several columns were required to complete a design. A second-order polynomial model was built for both responses. Optimal separations were also predicted using Derringer’s desirability functions. The optimum was found at 33 mM cyclodextrin and 16% (v/v) acetonitrile on two types of columns (with different packing times) leading to a strong reduction in analysis time for an equally good separation compared to the initial conditions. Measured and predicted responses were found comparable, indicating that acceptable models were obtained. 相似文献
43.
A brief treatment of 2-thiopyrimidine nucleosides (s2U∗) with trans-2-phenylsulfonyl-3-phenyloxaziridine (PSO) results in efficient substrate desulfurization leading to the corresponding 4-pyrimidinone analogues (H2U∗). The key transformation proceeds through oxidation of the 2-thiocarbonyl group to a sulfur oxyacid derivative and subsequent elimination of sulfur dioxide. 4-Pyrimidinone 1-β-d-riboside (H2U) has been transformed into the respective phosphoramidite, a ready-to-use monomer for the introduction of a modified nucleoside into an oligonucleotide chain. Moreover, the effective desulfurization of the 2-thiouridine nucleotide could be achieved directly at the oligonucleotide level, by treatment of the TdA(s2U)dGdC oligonucleotide with PSO, as verified by MALDI-TOF mass spectrometry. 相似文献
44.
一种新型两性表面活性剂的合成 总被引:2,自引:0,他引:2
两性表面活性剂分子既含有阳离子亲水基,又含有阴离子亲水基,因而有其它表面活性剂所不具备的优异性能。本文将月桂酸和N-(2-羟乙基)乙二胺热缩合脱水,得到2-十一烷基-1-(2-羟乙基)-2-咪唑啉(1)。接着在还原剂的作用下,咪唑啉环碳氮双键还原并开环得到一般方法难以合成的N,N-二取代乙二胺(2)。(2)通过甲酰化(3)季铵化,引入两性离子,得到 相似文献
45.
The reaction of (α-trimethylsilanylmethyl)cyclohexylidene esters with NsONHCO2Et and CaO produces the N-(ethoxycarbonyl)spiroaziridines which, after ring-opening, gives the corresponding β,β-disubstituted β-amino ester derivatives. The stereochemical outcome of the reaction is influenced by substituents on the cyclohexyl group. 相似文献
46.
47.
Pina Romaniello 《Journal of fluorine chemistry》2004,125(2):145-149
The effect of fluorine atoms on the second-order optical nonlinear response of 4-nitro-4′-methoxy-trans-stilbene and polyene derivatives containing up to three double bonds (n=1, 2, 3) has been investigated within a semiempirical context (PM3 Hamiltonian). Experimental data reported in literature indicate a βvec(SHG) value of 34, 47 and 76 (×10−30 esu) for n=1, 2, 3, respectively, at 0.65 eV in CHCl3 solutions. Our calculations show that fluorinating the nitrophenyl group the βvec(SHG) is doubled. Further increase in the second-order nonlinear response can be obtained fluorinating the CC bond linkers between the aromatic moieties.Besides, the effect of different donor-acceptor pairs has been studied and the results interpreted in the two-state model context.Some results concerning the third-harmonic generation (THG), γ (THG), are presented, and a possible interpretation proposed. 相似文献
48.
Toshikatsu Takanami 《Tetrahedron letters》2005,46(16):2893-2896
The catalytic Z-selective Claisen rearrangement of simple aliphatic allyl vinyl ethers can be achieved using a chromium(III) porphyrin complex, Cr(TPP)Cl, as a catalyst: Cr(TPP)Cl significantly enhances reversal of E-Z selectivity in the thermal Claisen rearrangement of allyl vinyl ethers, especially, 4,5- and 4,6-disubstituted derivatives, at low catalyst loading. 相似文献
49.
Vanessa Gouge 《Tetrahedron letters》2004,45(4):773-776
2,2-Difluoro-3-(2-hydroxy-1 R-phenylethylamino)-3 S-phenylpropionic acid 3, obtained by a Reformatsky-type reaction of ethyl bromodifluoroacetate with (4R)-2,4-diphenyloxazolidine, was used as a classical carboxylic acid in the Ugi reaction to prepare various difluorinated pseudopeptides 5a-n. Compounds 5 were then deprotected by hydrogenolysis to furnish difluorinated pseudopeptides 6. 相似文献
50.
Tetrabutylammonium cyanide has been used as non-metallic catalyst for the diastereoselective cyanosilylation of α-hydroxyketones derived from the chiral pool. This affords α-substituted-α,β-dihydroxynitriles with high levels of asymmetric induction. 相似文献