Visible-Light-Activated Asymmetric Addition of Hydrocarbons to Pyridine-Based Ketones
Yu Han, Tangyu Zhan, Yuqiao Zhou, Long Chen, Xiaohua Liu, Xiaoming Feng
Abstract
Enantioselective photoreduction of ketones with hydrocarbons is promising for the straightforward construction of chiral tertiary alcohols. But it is generally promoted by ultraviolet light via ketyl radical–alkyl radical coupling, which suffers from a competitive charge-transfer process and self/cross radical coupling reactions. An appropriate selection of a chiral catalyst that can alter the reaction pathway and deliver spatial selection is required. Accordingly, we disclosed a combined system involving Er(III)-based chiral Lewis acid catalysis, Ir(III)-based photoredox catalysis, and bromide-radical-mediated hydrogen atom transfer. The introduction of a bulky and nonredox chiral Lewis acid through the photoredox pathway enables the radical addition process and inhibits the above competitive reactions. The visible-light-promoted catalytic asymmetric alkylation of heteroaryl-based ketones with diverse hydrocarbons (mainly benzyl) delivered a variety of congested enantioenriched tertiary alcohols (up to 97% yield, 96% enantiomeric excess (ee)).