Asymmetric Synthesis of O‐Protected Acyloins Using Enoate Reductases: Stereochemical Control through Protecting Group Modification

O‐Protected cyclic acyloins were obtained in nonracemic form through asymmetric bioreduction of α,β‐unsaturated alkoxy ketones by using 11 different enoate reductases from the “Old Yellow Enzyme” family. The stereochemical outcome of the biotransformation could be switched by variation of the O‐protecting group or by the ring size of the substrate, which allows access to both stereoisomers in up to >97 % ee Whereas α‐alkoxy enones were readily accepted as substrates, β‐analogs were not converted. Overall, α‐alkoxy enones represent a novel type of substrate for flavin‐dependent ene‐reductases.