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Functionalization of dipyrromethanes via hetero-Diels–Alder reaction with azo- ...
Pereira, Nelson A. M.; Lemos, Américo; Serra, Arménio C.; Melo, Teresa M.V.D. Pinho e5,5′-Diethyl- and 5-phenyldipyrromethanes participate in cycloadditions with azo- and nitrosoalkenes giving dipyrromethanes with side chains containing open chain oximes and hydrazones. By controlling reaction stoichiometry it is possible to get mono or 1,9-disubstituted derivatives. The reported methodology gave access to a range of dipyrromethanes with good structural features for various applications. It was...
Nitrogen-Bridged Heterocycles via Cycloaddition of Non-Classical Heterocyclicfu...
Soares, Maria I. L.; Gomes, Clara S. B.; Melo, Teresa M. V. D. Pinho eThe [4π+2π] cycloaddition of non-classical heterocyclic-fused-[c]thiazoles was explored allowing the synthesis of a range of new nitrogen-bridged bi-, tri- and tetracyclic heterocyclic compounds namely, pyrazolo[1,5-a]pyridines, thiazolo[2,3,4-cd]pyrrolizines and indolizines. For the first time, one non-classical pyrrolo[1,2-c]thiazole was isolated and its structure determined by X-ray crystallography.
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...
Conformational Space and Vibrational Spectra of Methyl 4-Chloro-5-phenyl-1,3-ox...
Lopes, Susy; Nunes, Cláudio M.; Gómez-Zavaglia, Andrea; Melo, Teresa M. V. D. Pinho e; Fausto, RuiMethyl 4-chloro-5-phenyl-1,3-oxazole-2-carboxylate (MCPOC) has been synthesized and isolated in cryogenic matrices (argon and xenon). FTIR spectroscopy studies on the matrix isolated compound, supported by DFT(B3LYP)/6-311++G(d,p) calculations, allow for the identification of two low-energy conformers (I and II) of the molecule, which differ from each other in the orientation of the ester group relative to the ...
4-Halo-1,3-oxazoles: Unambiguous structural assignment of 2-halo-2-benzoyl-2H-a...
Lopes, Susy; Nunes, Cláudio M.; Fausto, Rui; Melo, Teresa M. V. D. Pinho ehttp://www.sciencedirect.com/science/article/B6TGS-4T9CD1T-2/2/97ced5a20f3a7c031b52a8483cc8ee76
Spectroscopic and theoretical investigation of the conformational space of a py...
Nunes, Cláudio M.; Lopes, Susy; Melo, Teresa M. V. D. Pinho e; Fausto, Ruihttp://www.sciencedirect.com/science/article/B6TGS-4V88FW3-1/2/a0eb253493e1ccafe49b75247f2ded74
Microwave-assisted generation and reactivity of aza- and diazafulvenium methide...
Soares, Maria I. L.; Melo, Teresa M. V. D. Pinho eAzafulvenium methides and diazafulvenium methides have been generated under microwave irradiation from 2,2-dioxo-1H,3H-pyrrolo[1,2-c]thiazoles and 2,2-dioxo-1H,3H-pyrazolo[1,5-c]thiazoles, respectively. Pericyclic reactions of these 1,7-dipole intermediates, namely, sigmatropic [1,8]H shifts, 1,7-electrocyclization or [8[pi]+2[pi]] cycloaddition led to the synthesis of a range of pyrrole and pyrazole derivative...
Substituent effects on the photolysis of methyl 2-carboxylate substituted aliph...
Gómez-Zavaglia, Andrea; Kaczor, Agnieszka; Cardoso, Ana L.; Melo, Teresa M. V. D. Pinho e; Fausto, RuiIn this study, the UV induced photochemical reactions of two 2H-azirines - methyl 2-chloro-3-methyl-2H-azirine-2-carboxylate (MCMAC) and methyl 3-methyl-2H-azirine-2-carboxylate (MMAC) - isolated in argon matrices are compared. For both compounds, irradiation with [lambda] > 235 nm led to observation of two primary photoprocesses: (a) CC bond cleavage, with production of nitrile ylides (P1-type products), and (...
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...
Unusual Photochemical C−N Bond Cleavage in the Novel Methyl 2-Chloro-3-methyl-2...
Gómez-Zavaglia, Andrea; Kaczor, Agnieszka; Cardoso, Ana L.; Melo, Teresa M. V. D. Pinho e; Fausto, RuiThe structure, preferred conformers, vibrational spectrum, and photochemical behavior of the novel azirine, methyl 2-chloro-3-methyl-2H-azirine-2-carboxylate (MCMAC) were investigated in low-temperature matrixes and in the neat solid amorphous state by infrared spectroscopy and quantum-chemical calculations. Two conformers of the compound were observed in argon, krypton, and xenon matrixes, in agreement with th...
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