Visible-Light-Enabled Ortho-Selective Aminopyridylation of Alkenes with N-Aminopyridinium Ylides.

By utilizing an underexplored reactivity mode of N-aminopyridinium ylides, we developed the visible-light-induced ortho-selective aminopyridylation of alkenes via radical-mediated 1,3-dipolar cycloaddition. The photocatalyzed single-electron oxidation of N-aminopyridinium ylides generates the corresponding radical cations that enable previously inaccessible 1,3-cycloaddition with a broader range of alkene substrates. The resulting cycloaddition adducts rapidly undergo subsequent homolytic cleavage of the N-N bond, conferring a substantial thermodynamic driving force to yield various β-aminoethylpyridines. Remarkably, amino and pyridyl groups can be installed into both activated and unactivated alkenes with modular control of ortho-selectivity and 1,2-syn-diastereoselectivity under metal-free and mild conditions. Combined experimental and computational studies are conducted to clarify the detailed reaction mechanism and the origins of site selectivity and diastereoselectivity.