RESUMO
We report the preparation and full characterization of a series of hydroxyl functionalized 1,2,3-triazolylidene-based PEPPSI complexes 2a-c and their catalytic application in the Suzuki cross coupling reaction of aryl chlorides/amides with boronic acids. Under basic reaction conditions, complexes 2a-c show a notable increase in their catalytic efficiency compared with two ether-wingtip functionalized PEPPSI analogues (3 and 4) and a commercially available NHC-Pd complex (5). The catalytic results suggest that deprotonation of the hydroxyl group in complexes 2a-c plays an important role in the overall process. Deprotonation of the alcohol moiety of complexes 2a-b with sodium tert-butoxide allows for the isolation of metallacycles 6a-b, which are proposed as the active species of cross coupling reactions.
RESUMO
This works reports the synthesis and characterization of diallyl(5-(hydroxymethyl)-1,3-phenylene) dicarbonate (HMFBA) and 5-(hydroxymethyl)-1,3-phenylene bis(2-methylacrylate) (HMFBM) monomers and its evaluation as Bis-GMA eluents in the formulation of composite resins for dental use. The experimental materials formulated with HMFBA and HMFBM monomers presented flexural strength values similar to those of the control group formulated with Bis-GMA/TEGDMA. Regarding volumetric contraction percentage, the values obtained of experimental materials with HMFBA was 1.88% and for HMFBM was 4.15%, both lower than control resin (4.68%). In the case of double bond conversion, the resin formulated with HMFBA monomer exhibited a greater degree of conversion (87%). Besides, the DMA analyses proved that the values for Tg guarantee a good mechanical performance at body temperature. The new resins formulated with HMFBA and HMFBM monomers exhibit a cellular viability close to 100%, which indicates the absence of cytotoxicity towards fibroblastic cells.
Assuntos
Resinas Compostas , Fibroblastos/metabolismo , Teste de Materiais , Polietilenoglicóis , Ácidos Polimetacrílicos , Animais , Linhagem Celular , Resinas Compostas/química , Resinas Compostas/farmacologia , Avaliação Pré-Clínica de Medicamentos , Fibroblastos/citologia , Camundongos , Polietilenoglicóis/química , Polietilenoglicóis/farmacologia , Ácidos Polimetacrílicos/química , Ácidos Polimetacrílicos/farmacologiaRESUMO
Long-range coupling constants (5) JHortho,OMe were measured in series of methoxyindoles, methoxycoumarins, and methoxyflavones by the modified J doubling in the frequency domain method. The COSY and NOESY spectra revealed the coupling of the -OMe group with a specific proton at the ortho position and its preferred conformation. Homonuclear (1) H-(1) H couplings were confirmed by irradiation of the -OMe signal. Density functional theory calculations of (5) JHortho,OMe using the modified aug-cc-pVTZ basis set evidenced that the Fermi contact term shows good agreement with the experimental J values. Accurate chemical shift and coupling constant values followed after iterative quantum mechanical spectral analysis using the PERCH software.
RESUMO
The reactions of 5-substituted indolylmalonates (2a-e), carrying an electron-withdrawing group at the N(1) position, with bromine in CCl(4) or AcOH are reported. These substrates undergo oxidation in competition with the well-known aromatic bromination. Under the two sets of conditions, with parent indolylmalonate (2a), chemospecific oxidation is observed, whereas with 5-hydroxyindolylmalonate (2c), bromination at the 4- and 6-position is the dominating reaction. Investigation of the products composition of several 5-substituted indolylmalonates revealed the following trend: with a 5-substituted electron-withdrawing group like fluorine, the indolylmalonate undergoes oxidation rather than bromination. In contrast, with a 5-substituted electron-donating group, like a hydroxyl group, the ring bromination occurs preferentially over the oxidation. When the 5-substituent is an alkoxyl group, a significant amount of brominated-oxidized products is obtained. Monitoring the oxidation reaction by mass spectrometry allowed the characterization of the 2-bromoindolylidenemalonate intermediate. A bromonium ion is considered as possible pathway in the formation of this intermediate. The conformation of unsymmetrical methoxyl and benzyloxyl substituents was determined from (1)H NMR spectra, single-crystal X-ray diffraction and ab initio calculations.
RESUMO
A method to determine the absolute configuration of 2,3-epoxy-2-methylbutanoate ester residues in natural products is presented, based on (i) the reduction of the ester function to yield a 2-methyl-1,2-butanediol, (ii) esterification of the obtained primary alcohol with either (R)-(+)- or (S)-(-)-Mosher's acid to afford the corresponding Mosher's ester, and (iii) 1H-NMR spectral comparison of the final product with that of the Mosher's esters prepared from 2-methyl-1,2-butanediols of known stereochemistry.