Photocatalytic Vicinal Aminopyridylation of Methyl Ketones by a Double Umpolung Strategy.

A photocatalytic double umpolung strategy for the vicinal aminopyridylation of ketones was developed using pyridinium N-N ylides. The inversion of the polarity of the pyridinium N-N ylides by single-electron oxidation successfully enables radical-mediated 1,3-dipolar cycloadditions with enolsilanes formed in situ from ketones, followed by homolytic cleavage of the N-N bond. Intriguingly, the nucleophilic amino and electrophilic pyridyl groups in the ylides can be installed at the nucleophilic α-position and electrophilic carbonyl carbon, respectively, which are typically inaccessible by their innate polarity-driven reactivity. This method accommodates a broad scope, and the utility was further demonstrated by the late-stage functionalization of complex biorelevant molecules. Moreover, the strategy can be successfully applied to enamides.