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 S_N1-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 S_N2(')-type oxidative addition of low-valent transition metals to most allylic electrophiles.