Mechanistic Investigation of the Nickel-Catalyzed Suzuki Reaction of N,O‑Acetals: Evidence for Boronic Acid Assisted Oxidative Addition and an Iminium Activation Pathway

The mechanism of a recently reported Suzuki coupling reaction of quinoline-derived allylic N,O-acetals has been studied using a combination of structural, stereochemical, and kinetic isotope effect experiments. The data indicate that C–O activation is facilitated by Lewis acid assistance from the boronic acid coupling partner and an ionic SN1-like mechanism accounts for oxidative addition. In this context, we demonstrate the first direct observation of oxidative addition to a quinolinium salt. Notably, this mechanism is distinct from the more commonly described SN2­(′)-type oxidative addition of low-valent transition metals to most allylic electrophiles.