Benzylic C(sp³)−H Phosphonylation via Dual Photo and Copper Catalysis

Abstract Alkyl phosphonates are important motifs in medicinal chemistry, yet their efficient synthesis by direct C(sp 3 )−H functionalization remains a challenge. Here, we report straightforward access to benzylic phosphonates by direct C(sp 3 )−H functionalization in a cross‐dehydrogenative‐coupling reaction between non‐specialized alkylarenes and unfunctionalized phosphites. Notably, the C−H substrates are used as the limiting reagents. The scope of benzylic C−H substrates is broad, and the mild reaction conditions allow for good functional group tolerance. Mechanistic studies indicate that the reaction proceeds via a radical pathway rather than the cationic pathway followed for specialized benzylic C−H substrates in previous methods.