Photoinduced [4+2] cycloaddition of dienes and quinonemethides.

A visible light-induced cycloaddition of 1,3-dienes and p -quinonemethides through EDA complexation is reported. The reaction does not require any external photocatalyst, oxidant or additive. The generality of the method is established through a broad substrate scope. This newly developed strategy presents an exciting prospect for the development of metal-free photocatalytic [4+2] cycloaddition reactions.