Favorskii rearrangements—I: One electron transfer from α′-enolate intermediates to 3O2 in aprotic,polar- protic and mixed media

Evidene for the trapping of α′-enolate intermediates in Favorskii rearrangements by one-electron transfer (ET) to ³O₂ is presented. The mechanism of the ET reaction has been elucidated from studied of the extent of ET trapping, compared to H/D exchange. The trapping efficiency (alkene/esters) was found tobe dependent on the reaction medium, the pK_a of the α′-C-acid, (a larger pK_a favouring greater ET) and the substrate concentration. Conclusions from this work of relevance to the mechanism of the Favorskii rearrangement are outlined.