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Cycloaddition of trifluoromethyl azafulvenium methides: synthesis of new triflu...
Nunes, Cláudio M.; Silva, Manuela Ramos; Beja, Ana Matos; Fausto, Rui; Melo, Teresa M.V.D. Pinho eThe chemistry of trifluoromethyl azafulvenium methides was explored leading to a new route to trifluoromethylpyrrole-annulated systems. The first evidence of azafulvenium methides acting as 1,3-dipoles is reported. These azafulvenium methides showed site selectivity in the reaction with strong electron-deficient dipolarophiles leading exclusively to 1,3-cycloadducts. In the cycloaddition with less-activated dip...
3-Oxoandrosta-4,6-dien-17[beta]-yl 2-methyl-1H-imidazole-1-carboxylate and 3-ox...
Silva, Manuela Ramos; Moreira, Vânia M.; Cardoso, Cláudia; Beja, Ana Matos; Salvador, Jorge A. R.The title compounds, C24H30N2O3, (I), and C24H34N2O3, (II), both contain an androstane backbone and a 2-methylimidazole-1-carboxylate moiety at the 17-position. Compound (I) contains two symmetry-independent molecules (denoted 1 and 2), while compound (II) contains just one molecule in the asymmetric unit. The C-C-O-C torsion angle that reflects the twisting of the 2-methylimidazole-1-carboxylate moiety from th...
Conformation of 17-chloro-16-formylandrosta-5,16-dien-3[beta]-yl acetate and 17...
Silva, Manuela Ramos; Moreira, Vânia M.; Cardoso, Cláudia; Beja, Ana Matos; Salvador, Jorge A. R.In the title compounds, C22H29ClO3, (I), and C21H29ClO2, (II), respectively, the B rings adopt a half-chair conformation and the D rings adopt an envelope conformation. A twist of the steroid skeleton of both compounds is observed. There is a positional disorder of the acetoxy group of (II), with the terminal atoms disordered over two positions with near equal occupancy. Quantum-mechanical ab initio calculation...
Chemistry of Diazafulvenium Methides in the Synthesis of Functionalized Pyrazoles
Melo, Teresa M. V. D. Pinho e; Nunes, Cláudio M.; Soares, Maria I. L.; Paixão, José A.; Beja, Ana Matos; Silva, Manuela RamosThe chemistry of diazafulvenium methides generated by the thermal extrusion of sulfur dioxide from 2,2-dioxo-1H,3H-pyrazolo[1,5-c] [1,3]thiazoles is described. The diazafulvenium methides unsubstituted at C-7 participate in [8π + 2π] cycloadditions giving pyrazolo-annulated heterocycles resulting from the addition across the 1,7-position. 1-Methyl-diazafulvenium methides and 7,7-dimethyl-diazafulvenium methides...
Synthesis, crystal structure and magnetic properties of an alternating manganes...
Silva, Manuela Ramos; Beja, Ana Matos; Paixão, José António; Martín-Gil, JesusA new 1D complex has been prepared and characterized. X-ray single crystal structure confirms that the Mn(II) ions assemble in alternating chains with Mn-Mn distances of 3.8432(13) and 4.4428(14) Å. A 3D network of hydrogen bonds links the chains together. The temperature dependence of the magnetic susceptibility reveals that this compound undergoes a magnetic transition and exhibits an antiferromagnetic intera...
Crystal structure and properties of l-tryptophanium hydrogen selenite
Paixão, José António; Silva, Manuela Ramos; Beja, Ana Matos; Eusébio, Ermelindal-Tryptophanium hydrogen selenite was synthesised and structurally characterised at room and low temperature. The aminoacid is positively charged with the amine and carboxylic group protonated. It adopts a staggered conformation with the N1 gauche to C4 that is gauche to C1. The anion displays a pyramidal conformation with three different Se-O bond lengths, one characteristic of a double bond, another of a sing...
Hexahydro-Pyrrolo[1',2',5':3,4,5]Thiazolo[3,4-c]Oxazol-1-ones: New Chiral Tricy...
Melo, Teresa M.V.D Pinho e; Lopes, Susana M.M.; Gonsalves, Antonio M. d'A Rocha; Kaczor, Agnieszka; Fausto, Rui; Paixao, Paixao, Jose A; Beja, Ana MatosA simple and efficient approach to the synthesis of the new chiral hexahydropyrrolo [1',2',5':3,4,5]thiazolo[3,4-c]oxazol-1-one ring system is reported. Infrared spectroscopy, quantum-chemical calculations and X-ray analysis allowed the stereochemistry assignment of (2aS,4aR,6aR)-2a,3,4,4a,6,6ahexahydropyrrolo-[ 1',2',5':3,4,5]thiazolo[3,4-c]oxazol-1-one. [ABSTRACT FROM AUTHOR]. Copyright of Letters in Organic...
N-Vinyl- and C-Vinylpyrroles from Azafulvenium Methides. Flash Vacuum Pyrolysis...
Melo, Teresa M. V. D. Pinho e; Soares, Maria I. L.; Gonsalves, António M. d'A. Rocha; Paixão, José A.; Beja, Ana Matos; Silva, Manuela Ramos1-Azafulvenium methides, generated from pyrrolo[1,2-c]thiazole-2,2-dioxides' thermal extrusion of sulfur dioxide, led to the synthesis of functionalized pyrroles. The intramolecular trapping of these transient 8π 1,7-dipoles in pericyclic reactions, namely sigmatropic [1,8]H shifts and 1,7-electrocyclization, allowed the synthesis of N-vinylpyrroles and C-vinylpyrroles which, under flash vacuum pyrolysis condit...
(R,R)-N-phenyl-3,4-bis(diphenylphosphino)pyrrolidine: an N-aryl pyrrolidine lig...
Gonsalves, António Manuel d'Albuquerque Rocha; Serra, Maria Elisa da Silva; Silva, Manuela Ramos; Beja, Ana Matos; Paixão, José AntónioThe N-aryl pyrrolidine diphosphine (R,R)-N-phenyl-3,4-bis(diphenylphosphino)pyrrolidine was obtained from natural tartaric acid. Contrary to our preliminary expectations, this new chiral ligand proved to be less selective than the corresponding N-benzyl pyrrolidine diphosphine. An attempted explanation of the observed behaviour based on the stereochemistry of the ligand as shown by X-ray crystallography is pres...
F---H···F hydrogen bond in diphenylguanidinium hydrogen bifluoride
Silva, Manuela Ramos; Paixão, José A.; Beja, Ana Matos; da Veiga, Luiz AlteThe crystal structure of C13H14N3+FHF- is reported. The structure contains the strong hydrogen-bonded system, the bifluoride anion F---H···F-. The geometry of this anion deviates significantly from linearity but has the H atom in an approximate centered position. The F···F distance is 2.293(3) Å, considerably less than twice the van der Waals radius of fluorine, as expected from a very strong hydrogen bond. ; ...
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