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(N)1-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(N)2(')-type oxidative addition of low-valent transition metals to most allylic electrophiles.