The Bu 4 NI/ t- BuOOH oxidative system is widely used in organic synthesis, but mechanistic principles underlying its reactivity are only partially explored. In this work, drawing on the example of the oxidative C–O coupling reaction between compounds with a carbonyl group and (or) a benzyl moiety with N -hydroxyphthalimide, it has been discovered that the coupling with the CH-acidic fragment of the carbonyl group proceeds via ionic mechanism, and the coupling with the benzyl fragment proceeds via radical mechanism. When dimethylacetamide is used as a solvent, the ionic process with the participation of the carbonyl group prevails, while in MeCN the radical process involving the benzyl moiety is realized along with the ionic process. For the oxidative C–O coupling with participation of the benzyl moiety without affecting the α-CH fragment of the carbonyl group, it is advisable to use PhI(OAc) 2 , Ce(NH 4 ) 2 (NO 2 ) 6 , or t‑ BuOO t- Bu as oxidants for which only radical pathway is characteristic.