Transition-metal Free Visible Light Photoredox-catalyzed Remote C(sp3)-H Borylation Enabled by 1,5-Hydrogen Atom Transfer

We describe a transition-metal free, photoredox-catalyzed borylation method of unactivated C(sp3)-H bonds via initiated 1,5-hydrogen atom transfer (HAT). The remote borylation was directed by 1,5-HAT of the amidyl radical, which was generated by photocatalytic reduction of hydroxamic acid derivatives. Substrates bearing primary, secondary and tertiary C(sp3)-H bonds could all be accommodated in this remote borylation protocol, giving moderate to good yields of the desired products (up to 92%), and a series of functional groups were tolerated. Mechanistic studies, including radical clock experiments and DFT calculations, gave detailed insight into the 1,5-HAT borylation process.