Biocatalytic Atroposelective Synthesis of Axially Chiral <i>N</i>‑Arylindoles via Dynamic Kinetic Resolution

A highly enantioselective biocatalytic dynamic kinetic resolution (DKR) of configurationally labile N-arylindole aldehydes is described. The DKR proceeds by atroposelective bioreduction of the carbonyl group catalyzed by commercial ketoreductases (KREDs), thus affording the corresponding axially chiral N-arylindole aminoalcohols, with excellent conversions and optical purities. The strategy relies on the racemization of the stereogenic axis that takes place thanks to a transient Lewis pair interaction between the NMe2 and the aldehyde groups. This protocol features a broad substrate scope under very mild conditions.