Visible-Light-Mediated Enantioselective Photoreactions of 3-Alkylquinolones with 4-O-Tethered Alkenes and Allenes.

The title compounds undergo intramolecular [2 + 2] photocycloaddition reactions when irradiated with visible light in the presence of a chiral sensitizer. Up to four defined stereogenic centers are formed in a single step (14 examples with a tethered alkene, 6 examples with an allene, 72-99% yield, 81-99% ee) at catalyst loadings as low as 0.5 mol %. The alkyl group in the 3-position is crucial for the success of the reaction as it leads to a significant decrease of the triplet energy.