Enantioselective Photocatalytic 3 + 2 Cycloadditions of Aryl Cyclopropyl Ketones

Control of stereochemistry in photocycloaddition reactions remains a substantial challenge; almost all successful catalytic examples to date have involved 2 + 2 photocycloadditions of enones. We report a method for the asymmetric 3 + 2 photocycloaddition of aryl cyclopropyl ketones that enables the enantiocontrolled construction of densely substituted cyclopentane structures not synthetically accessible using other catalytic methods. These results show that the dual-catalyst strategy developed in our laboratory broadens synthetic chemists' access to classes of photochemical cycloadditions that have not previously been feasible in enantioselective form.