Visible light-promoted construction of cage-like frameworks by sequential [2 + 2] cycloaddition

A sequential [2 + 2] cycloaddition of unsaturated N-acylindoles was developed under visible light irradiation in the presence of a photosensitizer, forming unprecedented cage-like medium-ring frameworks in high yields. By exploiting the distinct reactivity and selectivity of two types of olefins within the substrate, the transformation provides a single-step and atom-economical approach to such molecules with exclusive regio- and diastereoselectivity, excellent functional group tolerance, and mild reaction conditions. Experimental mechanistic and calculation studies suggest that this reaction proceeds through an energy transfer pathway in this double [2 + 2] cycloaddition process.