A cheap organocatalyst, 4‐OH‐TEMPO + NO 3 − , is presented for the aerobic oxidation of benzylic C(sp 3 )H bonds in ethers. The catalytic efficiency is attributed to the cooperative action of both the cation and anion moieties. The oxoammonium cation facilitates hydride abstraction from the C(sp 3 )H bond, generating a stabilized carbocation intermediate, which is subsequently attacked by water to form the CO bond. Meanwhile, the nitrate anion participates in a NO x /O 2 cycle, regenerating the oxoammonium cation from its reduced hydroxylamine form. Under mild reaction conditions, this salt catalyzes the oxidation of ethers to produce lactones or ketones in excellent yields, even on a 10 mmol scale. Control experiments confirm that the carbocation intermediate is essential to the reaction and that the oxygen atom in the product is derived from water.
Chen et al. (Fri,) studied this question.