Photocatalytic Phosphine‐mediated Hydroxymethylation of Alkenes With Formaldehyde Hydrate

ABSTRACT

The mild and convenient generation of unprotected hydroxymethyl radical from simple C1 feedstocks remains a fundamental challenge. Here we report a visible‐light‐induced, phosphine‐mediated hydroxymethylation of electron‐deficient alkenes using aqueous formaldehyde as the hydroxymethyl radical precursor. The reaction is enabled by single‐electron oxidation of phosphine to phosphine radical cation (PRC), which engages formaldehyde hydrate to release hydroxymethyl radical via β‐scission. Subsequent regioselective radical addition to C─C double bonds, single‐electron reduction, and protonation deliver hydroxymethylated products under mild conditions. The method accommodates electronically diverse cinnamates, heteroaryl alkenes, trisubstituted alkenes, and complex substrates, demonstrating broad functional‐group tolerance and potential application for late‐stage functionalization. This work provides a practical entry to radical hydroxymethylation from commercially available aqueous formaldehyde and establishes phosphine‐mediated deoxygenation as a good platform for C1 radical generation.