Photobiocatalytic benzylic C–H acylation enabled by the synergy of a thiamine-dependent enzyme, an organophotocatalyst and hydrogen-atom-transfer

Direct functionalization of abundant C(sp3)–H bonds is highly attractive. Photobiocatalysis offers promise for expanding enzyme reactivity, yet it has been limited to pre-activated radical precursors. Key challenges include the lack of robust activation modes for inert C(sp3)–H bonds under biocatalytic conditions and controlling the reactivity and stereochemistry of prochiral radicals. Here we report a triple activation strategy enabling photobiocatalytic C(sp3)–H bonds acylation with aldehydes. By synergistically combining hydrogen atom transfer for prochiral radical formation, organic dye-modulated single electron transfer, and an engineered thiamine-dependent enzyme, we have successfully introduced a radical acyl transferase (RATCH) for functionalizing C(sp3)–H bonds. This robust radical enzymatic system achieves benzylic C(sp3)–H / aldehyde C(sp2)–H oxidative coupling in a highly enantioselective manner (33 examples, up to 97% ee).