Asymmetric Hofmann–Löffler–Freytag-type reaction via a transient carbenium ion complex merging organocatalysis and photocatalysis

Carbenium ions have long been an important component in organic synthesis due to their indispensable role as intermediates. However, their inherent instability and remarkable reactivity pose notable challenges in achieving enantiocontrol. The use of ubiquitous C(sp³)–H bonds as precursors to achieve highly enantioselective transformations is a very important, yet less explored approach. Here we detail an asymmetric Hofmann–Löffler–Freytag-type reaction under visible-light irradiation, resulting in chiral Evans auxiliaries with excellent enantioselectivity. This protocol is distinguished by its high efficiency (turnover frequency, 154 h⁻¹) and broad functional group tolerance. Mechanistic investigations reveal that the readily available bisoxazoline catalysts can expedite the reaction through a hydrogen-bonding effect and regulate enantioselectivity by transient coordination with carbenium ion intermediates.