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71.
72.
Frédéric Bernicot Diego Maldonado Kabe Moen Virginia Naibo 《Journal of Geometric Analysis》2014,24(2):1144-1180
The dual purpose of this article is to establish bilinear Poincaré-type estimates associated with an approximation of the identity and to explore the connections between bilinear pseudo-differential operators and bilinear potential-type operators. The common underlying theme in both topics is their applications to Leibniz-type rules in Sobolev and Campanato–Morrey spaces under Sobolev scaling. 相似文献
73.
Charles Shearer Oriane Desaunay Stephen Zorc Alexis D. Richaud Shyam S. Samanta Nagalakshmi Jeedimalla Stéphane P. Roche 《Tetrahedron》2019,75(43):130606
4H-Pyrans (4H-Pys) and 1,4-dihydropyridines (1,4-DHPs) are important classes of heterocyclic scaffolds in medicinal chemistry. Herein, an indium(III)-catalyzed one-pot domino reaction for the synthesis of highly functionalized 4H-Pys, and a model of 1,4-DHP is reported. This alternative approach to the challenging Hantzsch 4-component reaction enables the synthesis of fused-tricyclic heterocycles, and the mechanistic studies underline the importance of an intercepted-Knoevenagel adduct to achieve higher chemoselectivity towards these types of unsymmetrical heterocycles. 相似文献
74.
Coumarin 314 free radical cation: formation, properties, and reactivity toward phenolic antioxidants
Aspée A Alarcon E Pino E Gorelsky SI Scaiano JC 《The journal of physical chemistry. A》2012,116(1):199-206
We have explored the photogeneration of the coumarin 314 radical cation by using nanosecond laser excitation at wavelengths longer than 400 nm in benzene, acetonitrile, dichloromethane, and aqueous media. In addition, time-resolved absorption spectroscopy measurements allowed detection of the triplet excited state of coumarin 314 (C(314)) with a maximum absorption at 550 nm in benzene. The triplet excited state has a lifetime of 90 μs in benzene. It is readily quenched by oxygen (k(q) = 5.0 × 10(9) M(-1) s(-1)). From triplet-triplet energy transfer quenching experiments, it is shown that the energy of this triplet excited state is higher than 35 kcal/mol, in accord with the relatively large singlet oxygen quantum yield (Φ(Δ) = 0.25). However, in aqueous media, the coumarin triplet was no longer observed, and instead of that, a long-lived (160 μs in air-equilibrated solutions) free radical cation with a maximum absorbance at 370 nm was detected. The free radical cation generation, which has a quantum yield of 0.2, occurs by electron photoejection. Moreover, density functional theory (DFT) calculations indicate that at least 40% of the electronic density is placed on the nitrogen atom in aqueous media, which explains its lack of reactivity toward oxygen. On the other hand, rate constant values close to the diffusion rate limit in water (>10(9) M(-1) s(-1)) were found for the quenching of the C(314) free radical cation by phenolic antioxidants. The results have been interpreted by an electron-transfer reaction between the phenolic antioxidant and the radical cation where ion pair formation could be involved. 相似文献
75.
76.
Alexis Morales Jochem Struppe Enrique Meléndez 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(3-4):263-270
The possible inclusion complexes of Cp2NbCl2 into α-, β-, and γ-CD hosts have been investigated. The existence of a true inclusion complex in the solid state was confirmed
by a combination of thermogravimetric analysis, FTIR, PXRD, and 13C CP-MAS NMR spectroscopies. The solid-state results demonstrated that α-cyclodextrin does not form inclusion complexes with
Cp2NbCl2 whereas β- and γ-cyclodextrins do form such complexes. PXRD, NMR, and thermal analysis showed that the organometallic molecules
of Cp2NbCl2OH are included in the cavities of β- and γ-cyclodextrins, possibly adopting a symmetrical conformation in the complex, with
each glucose unit in a similar environment. In solution, 1H NMR experiments suggest that niobocene has a shallow penetration on the β-CD leading to upfield shift on H-3 signal with
a minor perturbation on the H-5 proton while for γ-CD, both H-3 and H-5 are shifted upfield substantially. This suggests that
niobocene penetrates deeper into the γ-CD cavity than in the β-CD cavity, as a result of the cavity size.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
77.
N Rosas P SharmaC Alvarez E GómezY Gutiérrez M MéndezR.A Toscano L.A Maldonado 《Tetrahedron letters》2003,44(43):8019-8022
The condensation of substituted α-keto alkynes with p-nitrobenzaldehyde in the presence of lithium diisopropylamide (LDA) affords highly substituted 5,6-dihydro-4H-oxocin-4-ones in good yields. Surprisingly, no six-membered carbocycles were formed in this 8-endo-dig cyclization to the oxocinone system. 相似文献
78.
Polysubstituted indoles can be prepared directly from functionalized nitroalkanes under very mildly acidic conditions in a simple, one-pot, two-stage procedure. 相似文献
79.
A Direct CH/ArH Coupling Approach to Oxindoles,Thio‐oxindoles, 3,4‐Dihydro‐1 H‐quinolin‐2‐ones,and 1,2,3,4‐Tetrahydroquinolines 下载免费PDF全文
Dr. Timothy E. Hurst Ryan M. Gorman Pauline Drouhin Dr. Alexis Perry Prof. Richard J. K. Taylor 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(43):14063-14073
A copper(II)‐catalysed approach to oxindoles, thio‐oxindoles, 3,4‐dihydro‐1H‐quinolin‐2‐ones, and 1,2,3,4‐tetrahydroquinolines via formal C?H, Ar?H coupling is described. In a new variant, copper(II) 2‐ethylhexanoate has been identified as an inexpensive and efficient catalyst for this transformation, which utilises atmospheric oxygen as the re‐oxidant. 相似文献
80.
Leuthold LA Mandscheff JF Fathi M Giroud C Augsburger M Varesio E Hopfgartner G 《Rapid communications in mass spectrometry : RCM》2006,20(2):103-110
Desorption electrospray ionization mass spectrometry (DESI-MS) was used as a simple and rapid way to analyze drug tablets and powders without sample preparation. Experiments were performed with a home-made DESI source coupled to a triple-quadrupole linear-ion trap (QqQ(LIT)) mass spectrometer. Twenty-one commercial drugs as well as some illicit Ecstasy tablets and powders were analyzed. MS spectra almost exclusively showed the protonated or deprotonated ion of the drug after directing the pneumatically assisted electrospray onto the tablet's surface. With some tablets, inhomogeneity of the surface resulted in different spectra depending on the spot analyzed, thus showing that DESI could be used for imaging. Directly triggered MS/MS spectra were used for confirmatory analysis, with analysis times often below 10 s per tablet. For illicit Ecstasy tablets, DESI-MS, GC/MS and LC/MS analyses provided similar qualitative results for the main analytes. With MS/MS spectra library comparison or exact mass measurements, this technique could become very powerful for the rapid analysis of unknown tablets and shows the great potential of desorption techniques as an alternative to solution-based analysis. 相似文献