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Keywords:

  • asymmetric catalysis;
  • benzopyrane;
  • chiral ion pair;
  • oxocarbenium ion;
  • reduction
Thumbnail image of graphical abstract

A new light-driven asymmetric ion-pair catalysis procedure for the metal-free enantioselective hydrogenation of in situ generated pyrylium ions from readily available chalcones was developed (see scheme). The photo-assisted Brønsted acid catalyzed procedure has broad scope and allows, for the first time, access to valuable 4H-chromenes in good yields and with excellent enantioselectivities.