Visible-Light-Mediated Radical trans-Hydroboration of Alkynes with NHC Borane

Although the radical hydroboration of alkenes with N-heterocyclic carbene (NHC) borane is well documented, the radical hydroboration of alkynes, especially terminal alkynes, remains challenging. Herein, a photoredox-catalyzed radical trans-hydroboration of alkynes with NHC borane has been developed, which provided various alkenyl boron compounds in moderate to good yields. This protocol exhibits a broad substrate scope, as both internal and terminal alkynes were compatible. The synthetic value of this method was further demonstrated by its applicability in the late-stage modification of bioactive molecules. A preliminary mechanism for this reaction was proposed.