Benzylic C(sp)-H Phosphonylation via Dual Photo and Copper Catalysis.

Alkyl phosphonates are important motifs in medicinal chemistry, yet their efficient synthesis by direct C(sp)-H functionalization remains a challenge. Here, we report straightforward access to benzylic phosphonates by direct C(sp)-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.