Photochemically Initiated, Electron‐Transfer‐Catalyzed Diels‐Alder Reactions of Electron‐Rich Dienophiles

Photochemically excited triphenylpyrylium tetrafluoroborate catalyzes Diels‐Alder reactions that proceed via an electron‐transfer chain mechanism. By means of a “redox umploung”, an electron‐rich alkene (En) is transformed into the radical cation, which functions as an appropriate electron‐poor dienophile (Sens ⊕ = triphenylpyrylium). equation image