Using Na2CO3 at 5 mol% yielded compound 14 in 80% (Table , entry a), whereas only 63% of the γ-lactone product was formed with the same amount of Cs2CO3 (entry c). Stoichiometric amounts of Na2CO3 decreased the yield of 14 to 37%, while the reaction stopped with 1 equivalent of Cs2CO3. Either the water content of the bases (entries b and d) or the carbonate competition for cerium complexation of benzoate inhibits the reaction. The formation of peroxy-lactone 15, reported by Shirase et al. as the main product, upon the reaction of molecular oxygen from air with the carbon-centred radical resulting from a 1,5-hydrogen atom transfer (HAT) of the oxygencentred radical on benzoic acid, was not observed under our conditions. The investigation of the influence of water introduced into the reaction via the carbonate base on the reaction outcome is detailed in the Supporting Information.