INFIQC   05475
INSTITUTO DE INVESTIGACIONES EN FISICO- QUIMICA DE CORDOBA
Unidad Ejecutora - UE
artículos
Título:
Photochemical Electron-Transfer Generation of Arylthiirane Radical Cations with Tetranitromethane and Chloranil. Some Novel Observations
Autor/es:
MARCELO PUIATTI; JUAN E. ARGÜELLO; ALICIA B. PEÑÉÑORY
Revista:
EUROPEAN JOURNAL OF ORGANIC CHEMISTRY
Editorial:
Wiley-VCH Verlag GmbH & Co
Referencias:
Año: 2006 p. 4528 - 4536
ISSN:
1434-193X
Resumen:
The radical cations from 2,2,3,3-tetraphenyl-thiirane (1a), 2,2-bis-(4-methoxy-phenyl)-3,3-diphenyl-thiirane (1b) and trans-2,3-diphenyl-thiirane (1c) have been generated by photoinduced electron transfer (PET) reactions with tetranitromethane (C(NO2)4) and chloranil (CA). A charge-transfer complexes (CTC) absorption is observed by UV-Vis spectroscopy between thiiranes (1) and C(NO2)4, quenching studies with azulene, on the other hand, suggest that the ET reaction occurs between the triplet CA (3CA) and thiiranes. The photochemical reaction of the CTC between thiiranes 1 and C(NO2)4 yields mainly the corresponding alkenes from the fragmentation of the radical-cation intermediate (1.+), together with nitration on the phenyl rings. However, oxygen transfer to afford the sulfoxides is not found. A marked solvent effect is observed in this reaction, with favored cage coupling for CH2Cl2 (nitration derivatives as primary products) and non-cage product for CH3CN (the alkene as a primary product). The PET reactions between 1a-b and CA in the presence of CH3OH (or another possible oxygen-centered nucleophile) give the ketone derivatives through ring opening, followed by oxidative cleavage. Conversely, under the same experimental conditions, the thiirane 1c afforded only the trans-stilbene (2c). This different behavior was ascribed to a different spin density in the corresponding singled occupied molecular orbital (SOMO) of the radical cation. For 1c+. the spin density is concentrated at the sulfur atom, whereas for 1a-b.+ the charge is distributed in the aromatic rings.