Photochemical and Photophysical Behavior of Indolyl Anions in Photostimulated Intramolecular Arylation Reactions

ARGÜELLO, JUAN E; VAILLARD VICTORIA A.; ROBERTO A. ROSSI

Córdoba

Encuentro; XI ELAFOT, Encuentro Latinoamericano de Fotoquímica y Fotobiología; 2012

We have recently reported an efficient strategy to afford a family of 2-pyrrolyl and 2-indolyl benzoxazole by a photostimulated intramolecular O-arylation reaction. With the aim to explore the reaction mechanism of these valuable photoreactions, we studied anions from indolyl amides 1a-b, which leads to the formation of product 2. We have found that the reaction does not occur in the dark and is inhibited partially by the addition of good electron acceptors. Competition studies showed that the bromo derivative was 1.6 times more reactive than the chloro derivative. Moreover, the reaction also occurred when we used a non-electron donor base like NaH. We have studied the photophysical properties of indolyl anions 3a-c by steady state fluorescence and time resolved fluorescence measurements, determining the fluorescence quantum yields and fluorescence lifetimes dependency with the nature of the substituent X (X =H, Cl, Br). We have also explored the ability of anion 3c in intermolecular ET reactions by quenching experiments with halobenzenes. We have found a dynamic quenching between excited 3c and halobenzenes, following the reactivity order PhI>PhBr>PhCl. In view of these results, we propose that the reaction occurs by a photoinduced electron transfer (PET) from the indolyl anion to aryl moiety. A complete mechanistic picture of this cyclization reaction will be also discussed.