Photoexcited Hantzsch Ester and Cobalt Catalysis Enable Diastereo- and Enantioselective Allylation of Aldehydes

Herein, we present the diastereo- and enantioselective allylation of aldehydes with allylic carbonates by merging cobalt catalysis and photoexcited Hantzsch ester (HE) without the utilization of exogenous photocatalysts. Various (Z/E-mixed) linear and branched allylic carbonates as well as aryl and alkyl aldehydes are well compatible in this protocol, affording an array of homoallylic alcohols in good to high yields (up to 89%) with high diastereoselectivities (up to >20/1 dr) and enantioselectivities (up to 98% ee). Mechanistic studies revealed that the photoexcited HE could reduce cobalt directly, thus demonstrating its dual role as a photosensitizer and sacrificial reagent.