Enantioselective Visible Light-mediated Formation of 3-Cyclopropylquinolones via Triplet-sensitized Deracemization

摘要： 3-Allyl-substituted quinolones undergo a triplet-sensitized di-π-methane rearrangement 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.