Visible-light enabled synthesis of cyclopropane-fused indolines via dearomatization of indoles

An efficient synthesis of methylene-unsubstituted cyclopropane-fused indolines via photoredox catalyzed dearomative cyclopropanation of indole derivatives was developed. A broad range of indoles bearing a variety of functional groups were compatible with these mild conditions, affording the products in moderate to excellent yields. Asymmetric cyclopropanation was also realized with the assistance of a chiral auxiliary in good yield with excellent diastereoselectivity, followed by the removal of the auxiliary to give enantioenriched alcohol. The 5 mmol scale reaction and derivatizations of the products were successfully carried out to demonstrate the synthetic value of this reaction.