Enantioselective, Intermolecular [<sub>π</sub>2+<sub>σ</sub>2] Photocycloaddition Reactions of 2(1<i>H</i>)-Quinolones and Bicyclo[1.1.0]butanes
Morgane de Robichon, Thilo Kratz, Frederike Beyer, Julian Zuber, Christian Merten, Thorsten Bach
Abstract
1-Substituted bicyclo[1.1.0]butanes add enantioselectively to 2(1 H )-quinolones upon irradiation (λ = 366 nm) in the presence of a chiral complexing agent. A two-point hydrogen bond between the quinolone and the template is responsible for stereocontrol in the photocycloaddition reaction. The reaction leads to the formation of products with a chiral bicyclo[2.1.1]hexane skeleton in high enantiomeric excess (91–99% ee ). The chiral template can be almost quantitatively (97%) recovered and used in another reaction. A triplet reaction pathway is likely, and sensitization is a suitable tool if the reaction is to be performed with visible light (λ = 420 nm).