Enantioselective Radical Hydroacylation of α,β-Unsaturated Carbonyl Compounds with Aldehydes by Triplet Excited Anthraquinone

The synthesis of chiral ketones has been a long focus
of chemistry research. Enantioselective radical hydroacylation, as
a useful strategy to access various chiral ketones, was restricted
to the reaction with β-substituted alkenes, in which a β-stereocenter
was generated via a stereocontrolled radical addition
to prochiral alkene. Herein, we realized a highly enantioselective
radical hydroacylation of α-substituted α,β-unsaturated
carbonyl compounds through direct hydrogen atom transfer in the presence
of the photocatalyst anthraquinone and chiral N,N′-dioxide/metal complexes. This mild, robust method
provided a facile access to a wide array of chiral ketones with α-tertiary
stereocenters by using the readily available aldehyde as a hydroacylation
reagent. Based on the spectroscopy experiments and control experiments
together with DFT calculations, a hydrogen atom transfer/radical addition/enantioselective
reverse hydrogen atom transfer sequence was proposed.