共查询到20条相似文献,搜索用时 78 毫秒
1.
Michael Lorenz 《Tetrahedron letters》2007,48(16):2905-2907
The synthesis of the C23-C32 fragment of spirangien A is reported using Evans’ alkylation, Evans-Metternich aldol reaction and a substrate controlled stereoselective reduction. 相似文献
2.
Peter L. Simon Stephen K. Scott Serafim Kalliadasis John H. Merkin 《Journal of mathematical chemistry》2004,35(4):309-328
The stability of a premixed laminar flame supported by a general combustion reaction system is considered using the Evans function method. The spectrum of the linearised second-order differential operator is investigated in detail. The special structure of the differential equations due to an Arrhenius temperature dependence is exploited. It is shown that, for certain combustion systems, the limit of the Jacobian of the reaction terms as the travelling wave coordinate approaches the front and rear of the flame is a lower triangular matrix. For this type of system a simple geometrical method is shown for the study of the essential spectrum of the linearised operator, and for determining the domain of the Evans function. The results are applied to some representative combustion reactions. 相似文献
3.
The synthesis of the southern (C1′-C11′) fragment of pamamycin-635A, isolated from Streptomyces alboniger, was achieved via an Evans aldol reaction, a cis-selective iodoetherification and a stereospecific deiodination as the key steps. 相似文献
4.
《Journal of Coordination Chemistry》2012,65(12):1327-1334
A new organic–inorganic polyoxometalate compound [Co(2,2′-bipy)3]H[Al(OH)6 (Mo6O18)]?·?17H2O has been synthesized and characterized by elemental analysis, IR, UV spectra, thermogravimetry and differential thermal analysis (TG-DTA) and single-crystal X-ray diffraction analysis. The title compound crystallizes in a monoclinic, C2/c space group, with a?=?37.292(8), b?=?14.214(3), c?=?25.050(5)?Å, β?=?120.62(3), V?=?11426(4)?Å3, Z?=?8, F(000)?=?7200, D c?=?2.116?Mg?m?3, R?=?0.0748, wR 2?=?0.1853. Crystal structural analysis indicates that the asymmetric unit in the crystal structure of the title compound consists of one B-Anderson–Evans type heteropolyoxoanion, one octahedral [Co(2,2′-bipy)3]2+ coordination cation, seventeen water molecules of crystallization and a proton based on charge balance. The curves of TG-DTA indicate that weight loss of the title compound is divided into three stages. The third weight loss reveals that the backbone of heteropolyoxoanion decomposes at 744°C. 相似文献
5.
乙基曙红光度法测定西地那非的含量 总被引:3,自引:0,他引:3
在pH3.5~4.0的NaAc HCl缓冲介质中,西地那非与乙基曙红反应,形成离子缔合物,使乙基曙红溶液颜色发生明显改变,最大吸收波长在550nm,比乙基曙红红移了30nm,并在520nm处产生最大褪色作用,从而建立测定西地那非(Sild)的光度法。在最大褪色波长520nm处,西地那非浓度在0.2~2.0×10-5mol·L-1范围内遵守比耳定律,表观摩尔吸光系数ε520为2.44×104L·mol-1·cm-1,检出限为9.3×10-7mol·L-1,若用双波长叠加,则表观摩尔吸光系数ε520+550达4.53×104L·mol-1·cm-1,检出限达5.0×10-7mol·L-1。本法操作简便,体系稳定,灵敏度较高,选择性好,用于柠檬酸西地那非片(万艾可)中西地那非含量的测定,结果满意。 相似文献
6.
Resonance Rayleigh Scattering Method for the Determination of Raloxifene with Evans Blue 总被引:1,自引:0,他引:1
IntroductionInrecentyears ,resonanceRayleighscattering(RRS)methodasanewanalyticaltechniquehasbeenextensivelystudiedandwidelyusedtothedeterminationofsomebiologicalmacromolecules ,suchasnucleicacid ,1 4 protein5 8andheparin ,9aswellasinorganicion ,10 14 duetoitssi… 相似文献
7.
Chinni Yalamanchili Amar G. Chittiboyina Sateesh Chandra Kumar Rotte John A. Katzenellenbogen William G. Helferich Ikhlas A. Khan 《Tetrahedron》2018,74(16):2020-2029
For the first time, both antipodes of the isoflavans, equol and sativan were synthesized in >98% ee with good overall yields starting from readily available starting materials. The chiral isoflavan, (?)-equol is produced from soy isoflavones, formonentin and daidzein by the action of intestinal bacteria in certain groups of population and other chiral isoflavans are reported from various phytochemical sources. To produce these chiral isoflavans in gram quantities, Evans' enantioselective aldol condensation was used as a chiral-inducing step to introduce the required chirality at the C-3 position. Addition of chiral boron-enolate to substituted benzaldehyde resulted in functionalized syn-aldol products with >90% yield and excellent diastereoselectivity. Functional group transformations followed by intramolecular Mitsunobu reaction and deprotection steps resulted the target compounds, S-(?)-equol and S-(+)-sativan, with high degree of enantiopurity. By simply switching the chiral auxiliary to (S)-4-benzyloxazolidin-2-one and following the same synthetic sequence the antipodes, R-(+)-equol and R-(?)-sativan were achieved. Both enantiomers are of interest from a clinical and pharmacological perspective and are currently being developed as nutraceutical and pharmacological agents. This flexible synthetic process lends itself quite readily to the enantioselective syntheses of other biologically active C-3 chiral isoflavans. 相似文献
8.
Novel routes for the synthesis of spiro derivatives of Meldrum’s acid and 2-substituted malonic acid derivatives have been developed. Meldrum’s acid was monoalkylated using a Michael addition reaction. Mono-Michael adducts were then alkylated using substituted haloalkanes, which on condensation gave spiro derivatives of Meldrum’s acid. Bis Michael addition of Meldrum’s acid with 1,5-diaryl-1,4-pentadien-3-one gave directly a spiro derivative of Meldrum’s acid. These compounds and bis alkylated Meldrum’s acid derivatives, on acidic methanolysis gave 2-substituted malonic acids. 相似文献
9.
10.
Huan Liang 《Tetrahedron》2010,66(31):5884-11851
The oxidative amidation of phenols effects the conversion of appropriately substituted phenols into 4-amidodienones (‘para-oxidative amidation’) or 2-amidodienones (‘ortho-oxidative amidation’) by the action of hypervalent iodine reagents. The reagent, (diacetoxyiodo)benzene (‘DIB’) is especially effective in these transformations. This paper focuses on techniques for the desymmetrization of the dienoes thus obtained, leading to the stereocontrolled creation of N-substituted spiro carbons. The methodology creates new opportunities in alkaloid synthesis, as apparent from a number of examples. 相似文献
11.
Salen-chromium(III) complexes bearing sterically demanding substituents at the 3 and 3′ positions are applied for the oxo-Diels-Alder reaction of various aldehydes with Danishefsky’s diene. The readily-accessible complex bearing a bulky 3-phenylpent-3-yl substituent revealed its potential affording the cycloadducts with improved reactivity and excellent selectivities up to 96% ee, being considerably superior to the classic Jacobsen’s catalyst. 相似文献
12.
Certonardosterol D2, a polyhydroxysterol isolated from starfish Certonardoa semiregularis with exceptionally potent antitumor activity, was stereoselectively synthesized from natural rich diosgenin via the protocol of Julia olefination and Evans aldol reaction. 相似文献
13.
In the benzylation of a m-xylylene-bridged calix[6]arene tetrol, the first example of the ‘partial cone’ isomer of a calix[6]arene was obtained in addition to the corresponding cone and 1,2,3-alternate isomers, and its structure was established by X-ray crystallographic analysis. The synthesis and crystal structure of the ‘inverted cone’ isomer as well as its thermal conversion to the ‘normal cone’ isomer are also described. 相似文献
14.
The first synthesis of Tröger’s base analogues bearing three and four atoms in the apical strap is reported, leading to a dramatic change in the shape of the aromatic scaffold with respect to the Tröger’s base framework. 相似文献
15.
The titration of a multicomponent mixture can be described either with de Levies integral representation [1] or with Moisios and Heikonens derivative representation [2]. In the latter method an experimental titration curve is numerically differentiated and the computations are based on the buffer capacity. Numerical calculations demonstrate that the results of these two methods coincide very well. 相似文献
16.
依文思蓝光度法测定阿昔洛韦及其分析应用 总被引:1,自引:0,他引:1
在pH 5.74 HAc-NaAc缓冲介质中, 阿昔洛韦(ACV)与依文思蓝(EB)反应形成离子缔合物, 溶液颜色发生明显改变, 最大褪色波长为638 nm. 在此波长处, 阿昔洛韦的浓度与褪色程度呈良好线性关系, 从而建立测定阿昔洛韦的光度法. 在最大褪色波长处, 阿昔洛韦的浓度在0~2.01×10-5 mol/L范围内遵守比尔定律, 表观摩尔吸光系数1.71×104 L·mol-1·cm-1, 检出限为7.47×10-7 mol/L. 方法具有较高的灵敏度和良好的选择性, 可用于实际药品、血浆及尿液中阿昔洛韦的测定. 相似文献
17.
The Heck arylation of acrolein with a variety of condensed aryl and heteroaryl halides is described. Depending on the substrate, up to 87% isolated yield to the expected aldehydes was achieved. When the reaction was run on diethylacetal acrolein, the choice of catalytic system dramatically affected the selectivity of the reaction: the catalyst system based on Herrmann’s palladacycle complex gave mainly saturated esters 2, whereas Cacchi’s conditions led to the formation of α,β-unsaturated aldehydes 1. 相似文献
18.
A stereoselective synthesis of the C3–C12 subunit of the tumor growth inhibitors laulimalide is disclosed. The key steps of the synthesis include asymmetric alkylation using Oppolzer’s protocol and an asymmetric hetero-Diels–Alder reaction using Jacobsen’s catalyst. Substrate controlled diastereoselective Luche reduction followed by Ferrier type reactions are other key steps. 相似文献
19.
Ali Hashem Essa 《Journal of organometallic chemistry》2007,692(22):4917-4920
The correlation analysis of Mulliken charge (QM) calculated by using density functional theory (B3LYP/STO-3G) calculations of 1-(4-azido-5-hydroxymethyl-tetrahydro-selenophen-2-ylmethyl)-5-substituted-1H-pyrimidine-2,4-dione, were done by using mono substituent parameter (Hammett’s model), and dual substituent parameter (Taft’s, Reynolds’, and Swain’s models). The dual substituent parameter correlations of the QM data gave no significant improvement over single parameter correlations, the best correlation observed with the Taft’s Model as compared with the Swain’s and Reynolds’ Models, respectively. The correlation analysis of Mulliken charge can be used successfully to demonstrate the existence or absence of the interaction between the oxygen of the carbonyl group and selenium atom. 相似文献
20.
The authors recently published works in which the use of two novel equations for modeling the dispersive kinetics observed in various solid-state conversions are described. These equations are based on the assumptions of a ‘Maxwell-Boltzmann (M-B)-like’ distribution of activation energies and a first-order rate law. In the present work, it is shown that it may be possible to expand the approach to include mechanisms other than first-order, i.e. some of those commonly encountered in the field of thermal analysis, thus obtaining ‘dispersive versions’ of these kinetic models. The application of these dispersive kinetic models to the slightly sigmoidal, isothermal conversion-time (x-t) data of Rodante and co-workers for the degradation of the antibiotic, oxacillin, is described. This is done in an effort to test the limitations of the proposed dispersive models in describing kinetic data which is not clearly sigmoidal (i.e. as shown in previous works). Finally, it is demonstrated that, using graphical analysis, the typically sigmoidal x-t plots of first-order dispersive processes are the direct result of (asymmetric) activation energy distributions that are either ‘∩-shaped’ (for heterogeneous conversions) or ‘∪-shaped’ (for homogeneous conversions) in appearance, i.e. when the activation energy is plotted as a function of conversion. This finding lends support to the founding hypothesis of the authors’ approach for modeling dispersive kinetic processes: the existence of ‘M-B-like’ distributions of activation energies. 相似文献