Reductive Cross-Coupling of α-Oxy Halides Enabled by Thermal Catalysis, Photocatalysis, Electrocatalysis, or Mechanochemistry

Herein, we report a reductive cross-coupling reaction of α-oxy halides, simply generated from aldehydes, with a series of C(sp2)- and C(sp)-electrophiles. A wide range of aryl and heteroatom aryl halides, vinyl bromides, alkynyl bromides, and acyl chlorides react with unhindered and hindered aldehyde-derived α-oxy halides by providing protected alcohols as well as α-hydroxy ketones. Noteworthy, the reductive couplings are achieved not only through thermal catalysis with the use of metal reductants but also by photocatalysis, electrochemistry, and mechanochemistry. The unrestricted interchange of the four strategies indicates their underlying mechanistic similarities. The generation of NiI intermediate is proposed to be the key point for ketyl radical formation via a single-electron transfer (SET) event, which was rationalized by an array of control experiments and density functional theory (DFT) calculations.