Borane Exchange Enables Photocatalytic Alkylation of Pyridylic C(sp 3 )−H Bonds with Olefins

Comprehensive Summary Direct C(sp 3 )−H alkylation of alkylpyridines provides an efficient route to C(sp 3 )‐rich pyridine motifs, which are highly prevalent in pharmaceuticals and agrochemicals. While numerous ionic methods have been developed, they typically require strong bases, elevated temperatures, or pre‐functionalized substrates. Here, we report a photocatalytic strategy for pyridylic C(sp 3 )−H alkylation via in situ borane exchange between pyridine substrates and triphenylphosphine‐borane. This method operates under mild conditions, avoids the need for strong bases or metal catalysts, and accommodates both styrenes and unactivated alkenes as coupling partners. Mechanistic studies revealed that borane exchange enhances the acidity of the C(sp 3 )−H bonds, thereby enabling rapid deprotonation and subsequent single‐electron oxidation to generate key pyridylic radical intermediates.