Recently, we have shown that 8 can be replaced with aerial O2, an oxidant that generates water as the sole by-product, using a system of electron transfer mediators (ETMs) for the synthesis of various esters and dihydropyranones. The system of ETMs circumvents the high energy barriers normally associated with direct aerobic oxidation by creating a low energy pathway for the electrons to flow from the substrate to oxygen. It is worth noting, that by using an ETM-system, one can typically avoid side-reactions associated with aerobic NHC catalysis, such as, acid formation, homo-coupling and internal redox reactions. This selectivity can be attributed to a kinetic preference for oxidation of the homoenolate to the acyl azolium by the ETMs.