Organic syntheses often rely on C–C bond-forming reactions to create complex structures. However, strategically breaking a C–C bond can also be useful in synthesis. This can be challenging due to the low reactivity of C–C bonds.

Peng Hu, Sun Yat-Sen University, Guangzhou, China, and colleagues have developed a visible-light-promoted, iron-catalyzed reaction of alcohols that gives ketones or aldehydes via a C–C bond cleavage (pictured). The team converted different cyclic or linear alcohols in the presence of FeCl₃ as a catalyst, tetrabutylammonium chloride (TBACl) as a source of chloride ions, bis(2,4,6-triisopropylphenyl) disulfide (TRIP₂S₂) as a radical source, and 2,4,6-collidine to bind the formed HCl under a blue LED. They used tertiary, secondary, and primary alcohols with a wide range of substituents.

The desired products were obtained in moderate to excellent yields. The reaction has a broad substrate scope and good functional group tolerance. The researchers propose that the mechanism proceeds via a pathway promoted by a chlorine radical, which is generated from [FeCl₄]⁻ upon excitation by light. This chlorine radical reacts with the alcohol to generate an alkoxy radical, followed by the C–C bond breaking and a hydrogen-atom transfer to give the desired products.

• Iron-Catalyzed C–C Single-Bond Cleavage of Alcohols,
  Wei Liu, Qiang Wu, Miao Wang, Yahao Huang, Peng Hu,
  Org. Lett. 2021.
  https://doi.org/10.1021/acs.orglett.1c03137