How is Microwave Irradiation Involved in the SRN1 Iniciation?

DANIEL A. CAMINOS; ALEXIS D. GARRO; SILVIA M. SORIA CASTRO; ALICIA B. PEÑÉÑORY

Conferencia; XIII Conferencia Latinoamericana de Fisico-Química Orgánica; 2015

Microwave heating devices combined with process that involves an electron-transfer (ET) step to generate radical anions and radicals to achieve new C-C bonds, such as SRN1, are attractive in pharmaceutical and fine chemistry offering a faster and safer synthetic methodology than conventional procedures. Recently we report the use of microwave irradiation for the formation of new C-C bond in the alpha-arylation of aromatic ketones and acetamides by the SRN1 mechanism. The microwave-induced reaction showed many advantages such as simplicity, shorter times, broad substituents compatibility and a better performance in the heterocyclic synthesis as compared to photoinduced reactions. The aim of the present work has been to explore the reaction mechanism under microwave irradiation and its role in the reaction. With this purpose we investigate the coupling reaction between acetophenone enolate anion and PhI at different microwave irradiation conditions. The model coupling reaction is accelerated by microwave irradiation and this increase in reaction rate is only ascribed to thermal effects. The coupling reaction gave the substitution product 1,2-di-phenylethanone in a 50 % yield when microwave irradiation allowed to reach a reaction temperature range of 70-120 °C, independently of the microwave pulse. The presence of ionic and dipolar species are not involved in the initiation process as molecular radiators. The excess of tBuOK in the reaction medium also acts as electron donor helping to generate radicals.