Enantioselective Visible‐Light‐Mediated Formation of 3‐Cyclopropylquinolones by Triplet‐Sensitized Deracemization

3‐Allyl‐substituted quinolones undergo a triplet‐sensitized di‐π‐methane rearrangement reaction to the corresponding 3‐cyclopropylquinolones upon irradiation with visible light (λ=420 nm). A chiral hydrogen‐bonding sensitizer (10 mol %) was shown to promote the reaction enantioselectively (88–96 % yield, 32–55 % ee). Surprisingly, it was found that the enantiodifferentiation does not occur at the state of initial product formation but that it is the result of a deracemization event. The individual parameters that control the distribution of enantiomers in the photostationary state have been identified. Mirror mirror on the wall, where has the other enantiomer gone? Catalyst 2 establishes an equilibrium between the two enantiomers 1 and ent‐1 in which one enantiomer prevails (up to 55 % ee). The deracemization is responsible for the enantioselective formation of 3‐cyclopropylquinolones from 3‐allyl‐substituted quinolones.