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Experimental and theoretical studies of the second- and third-order NLO propert...
Silva, Pedro S. Pereira; Ouazzani, Hasnaa El; Pranaitis, Mindaugas; Silva, Manuela Ramos; Arranja, Cláudia T.; Sobral, Abilio J. F. N.A new semi-organic compound, 6-aminoquinolinium iodide monohydrate (I), has been synthesized and characterized by single crystal X-ray diffraction, UV–vis absorption and fluorescence spectroscopy and nonlinear optical (NLO) measurements. The second- and third-order NLO responses were investigated with the second- and third-harmonic Maker fringes techniques, carried out on thin films at a fundamental wavelength ...
5β,6β-Epoxy-17-oxoandrostan-3β-yl acetate and 5β,6β-epoxy-20-oxopregnan-3β-yl a...
Pinto, Rui M. A.; Salvador, Jorge A. R.; Paixão, José A.In the title compounds, C21H30O4, (I), and C23H34O4, (II), respectively, which are valuable intermediates in the synthesis of important steroid derivatives, rings A and B are cis-(5β,10β)-fused. The two molecules have similar conformations of rings A, B and C. The presence of the 5β,6β-epoxide group induces a significant twist of the steroid nucleus and a strong flattening of the B ring. The different C17 subst...
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...
A ladder type structure: Rubidium diphenylacetate diphenylacetic acid
Silva, Manuela; Beja, Ana; Paixão, José A.; Domingos, Sérgio R.; Martín-Gil, JesúsA new rubidium complex, rubidium diphenylacetate diphenylacetic acid has been synthesised and characterised by single-crystal X-ray diffraction: triclinic, P $$\bar1$$ with a=7.437(3) , b=12.377(4) , c=14.384(3) , a=107.08(2), ß=103.67(2), ?=96.95(3), Mr=508.93, V=1203.6(6) 3, Z=2. The diphenylacetic molecules bridge the metallic ions forming an infinite ladder structure. Two strong hydrogen bonds link the orga...
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...
Vitaminas lipossolúveis em alimentos: uma abordagem analítica
Paixão,José A. da; Stamford,Tânia L. M.This study concerns certain problems inherent to the determination of fat-soluble vitamins in food, from extraction methods to identification and quantification. The discussion involves the main official and unofficial extraction methods coupled with spectrophotometric and HPLC techniques in which vitamins samples are obtained through liquid-liquid-solid and liquid-liquid-solid-solid extraction, indispensable t...
Synthesis of tricyclic isoindoles and thiazolo[3,2-c][1,3]benzoxazines
Pinho e Melo, Teresa M. V. D.; Santos, Catarina I. A.; Rocha Gonsalves, António M. dA.; Paixão, José A.; Beja, Ana M.The thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in Ac2O led to novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles and chiral (9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindoles were obtained on FVP. Starting from -cysteine methyl ester (3R,10bR)-5-oxo-2,3-dihydro-10bH-[1.3]thiazolo[3,2-c][1,3]benzoxazines were obtained as single stereoisomers. The t...
Oxidation of Δ4- and Δ5-Steroids with Hydrogen Peroxide Catalyzed by Porphyrin ...
Rebelo, Susana L. H.; Simões, Mário M. Q.; Neves, M. Graça P. M. S.; Silva, Artur M. S.; Cavaleiro, José A. S.; Peixoto, Andreia F.In this paper we describe a new environmentally friendly method to promote the stereoselective epoxidation of Delta4- and Delta5-steroids. Metalloporphyrins efficiently catalyze the epoxidation reactions of 17beta-acetoxy-4-androstene (1), 4-cholestene (2) and 3beta-acetoxy-5-cholestene (3) in the presence of H2O2 as oxygen donor. Modeling the molecular structure of the porphyrin as well as the central metal al...
Novel Asymmetric Wittig Reaction: Synthesis of Chiral Allenic Esters
Melo, Teresa M. V. D. Pinho e; Cardoso, Ana L.; Gonsalves, António M. d'A. Rocha; Pessoa, João Costa; Paixão, José A.; Beja, Ana M.Wittig reactions between 10-(phenylsulfonyl)isobornyl (triphenylphosphoranylidene)acetates (1 and 6) and ketenes resulted in asymmetric induction, with the selective synthesis of allenes with axial chirality. Use of the (1R)-(-)-10-(phenylsulfonyl)isoborneol unit allows the synthesis of allenes with S configuration, whereas use of the (1S)-(+)-10-(phenylsulfonyl)isoborneol unit produces allenes with R configura...
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