The greenhouse gas carbon dioxide can serve as a useful chemical feedstock. Most methods for the incorporation of CO₂ into valuable chemicals are based on a two- or six-electron reduction of CO₂. The four-electron reduction of CO₂, in contrast, is rarely used in organic synthesis.

Chanjuan Xi, Tsinghua University, Beijing, China, and colleagues have developed a selective four-electron reduction of CO₂ in the presence of thiols to generate dithioacetals (pictured). The team reacted a range of aromatic and aliphatic thiols with CO₂ (1 atm), using NaBH₄ as a reductant and 1,4-dioxane as the solvent. Iodine was used as an additive.

The desired thioacetals were obtained in moderate to excellent yields and the reaction could be scaled up to the gram scale. The developed reaction selectively converts CO₂ into a methylene unit and forms two C–S bonds simultaneously. According to the researchers, future work will focus on the reaction mechanism.

• Reduction of CO₂ into Methylene Coupled with the Formation of C–S Bonds under NaBH₄/I₂ System,
  Zhiqiang Guo, Bo Zhang, Xuehong Wei, Chanjuan Xi,
  Org. Lett. 2018.
  https://doi.org/10.1021/acs.orglett.8b02730