Photoenzymatic Hydroalkylation Enables Streamlined Access to Aryl Glutarimide Precursors

We describe a photoenzymatic hydroalkylation reaction that enables the efficient and stereocontrolled synthesis of aryl glutarimide precursors—chemically and configurationally robust entry points to bioactive agents for targeted protein degradation. Screening of flavin‐dependent “ene”‐reductases identified GluER HA rac , a G. oxydans variant, as an efficient and substrate‐tolerant catalyst, granting access to >30 (hetero)aryl glutarimide precursors. A directed evolution campaign then furnished a hexamutant, GluER HA ent , that delivers the products in up to 93:7 enantiomeric ratio. Mechanistic experiments revealed a pathway that departs from the hydrogen atom transfer mechanism previously established for related systems, proceeding instead via radical–polar crossover followed by enantioselective proton transfer from an active‐site tyrosine residue. Collectively, these studies establish a biocatalytic platform for advancing the synthesis and diversification of glutarimide‐containing degraders.