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Sperança A Godoi B Pinton S Back DF Menezes PH Zeni G 《The Journal of organic chemistry》2011,76(16):6789-6797
A series of 4-Se-(Te, S)-isochromenones and 3-substituted isochromenones were synthesized in good yields via FeCl(3)-mediated cyclization of alkynylaryl esters with different diorganyl dichalcogenides. This methodology was carried out at room temperature, using inexpensive and environmentally friendly iron salts as metallic source and under air atmosphere. The reaction showed to be tolerant to a range of substituents bonded into the aromatic ring of the diorganyl dichalcogenides as well as to alkyl groups directly bonded to the chalcogen atom. Alternatively, the cyclization reaction of 2-alkynylaryl esters with FeCl(3), in the absence of diorganyl dichalcogenide, gave the isochromenones without the chalcogen moiety in the structure. This approach proved to be highly regioselective, providing only six-membered ring products, once the possible five-membered products were not observed in any experiments. 相似文献
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Llohann D. Sperança 《Journal of Geometric Analysis》2018,28(3):2206-2224
We prove that, under reasonable conditions, odd co-dimension Riemannian foliations cannot occur in positively curved manifolds. 相似文献
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L. D. Sperança 《Archiv der Mathematik》2011,97(5):495-497
We use an explicit generator of π
6(S
3) to construct a homotopy 10-sphere with an effective SO(4) action that does not bound a parallelizable manifold. 相似文献
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Éverton Berwanger Balbom Fabiane Gritzenco Adriane Sperança Marcelo Godoi Diego Alves Thiago Barcellos Benhur Godoi 《Tetrahedron》2019,75(30):4017-4023
This work describes the copper-catalyzed Csp-chalcogen bond formation through cross-coupling reactions of propynylbenzamides and diorganyl dichalcogenides at room temperature, under open atmosphere. Generally, the reactions have proceeded very smoothly, affording the new class of organochalcogen-containing propynylbenzamides in good yields. Notably, this protocol showed to be tolerant to neutral, electron-donating and electron-withdrawing substituents present in both reaction substrates. In addition, the applicability of the carbon-chalcogen bond as a reactive site has been proved by successfully employment of the N-methyl-N-(3-(butylselanyl)prop-2-yn-1-yl)benzamide as a precursor in palladium-catalyzed Suzuki and Sonogashira type reactions. 相似文献
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Speranţa Vlădoiu 《Complex Analysis and Operator Theory》2017,11(8):1905-1916
We give a method to associate a right Markov process to a resistance form, that is different from the one based on the regularity assumption for the associated Dirichlet form. We use tools from potential theory associated to resolvents of kernels and cones of potentials (H-cones). The induced capacity and processes obtained by time change with the inverses of continuous additive functionals also occur. 相似文献
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Wavelength dispersive X‐ray fluorescence (WDXRF) and chemometric investigation of human hair after cosmetic treatment 下载免费PDF全文
Mônica Cardoso Santos Marco Aurelio Sperança Fabíola Manhas Verbi Pereira 《X射线光谱测定》2018,47(3):252-257
Variations in the chemical composition of 63 different human and 6 different synthetic hair samples were investigated using wavelength dispersive X‐ray fluorescence (WDXRF) spectra profiles. To evaluate the effect of cosmetic treatment on the strands, the human hair samples were bleached, but the synthetic ones were not. To better investigate the data, exploratory analyses were calculated using principal component analysis for the WDXRF spectra. Eight normalizations/standardizations were applied in the WDXRF to verify the clustering tendency. Bleaching was tested, because it is one way in which people mask their real hair color. After the data were standardized, an enhancement of the data discrimination was verified. Furthermore, the explained variance was higher in the first principal components. The WDXRF spectra were able to distinguish samples with distinct features, including synthetic, dyed, and straightened hair. The findings of this study hold promise for forensics due to desirable aspects such as nondestructivity and the possibility of a large hair sample database. 相似文献
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