Enantioselective Hydroalkylation of Alkenylpyridines Enabled by Merging Photoactive Electron Donor-Acceptor Complexes with Chiral Bifunctional Organocatalysis

The potential of electron donor-acceptor (EDA) complex photochemistry has recently been recognized in visible light-induced photocatalyst-free radical reactions. The design of catalytic asymmetric reactions driven by EDA complexes remains a substantial challenge, and existing examples are limited to sole activation modes with aminocatalysts or phase-transfer catalysts. Herein, we demonstrate that chiral bifunctional hydrogen-bonding catalysis can realize the asymmetric reaction of an EDA complex via dual activation modes and afford vicinal tertiary stereocenters at the beta,gamma-positions of pyridines in high yields with good enantio-and diastereoselectivities. Mechanistic studies suggest that the crucial success factor for this transformation is the use of chiral phosphoric acid (CPA), which not only accelerates the in situ formation of EDA aggregates between redox-active esters (RAEs) and Hantzsch esters (HEs) but also provides proper substrate activation and asymmetric induction.

Automated summary

The potential of electron donor-acceptor (EDA) complex photochemistry in visible light-induced photocatalyst-free radical reactions has recently been recognized. However, designing catalytic asymmetric reactions driven by EDA complexes remains challenging. Existing examples are limited to single activation modes with aminocatalysts or phase-transfer catalysts. In this study, chiral bifunctional hydrogen-bonding catalysis is demonstrated to enable the asymmetric reaction of an EDA complex via dual activation modes, resulting in the formation of vicinal tertiary stereocenters at the beta,gamma-positions of pyridines with high yields and good enantio- and diastereoselectivities.