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.