In a study published in J. Am. Chem. Soc., a group led by Prof. LI Gang at Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences reported an interesting protocol of visible-light-driven reductive arylcarboxylation of styrene derivatives with CO₂ (1 atm) and aryl halides.

This is the first example of the visible-light-driven Meerwein-arylation-type difunctionalization of alkenes using aryl halides, which are often bench-stable, inexpensive and widely available.

The researchers found that a wide range of aryl iodides and bromides were viable with this reaction to produce arylcarboxylation products of various styrene derivatives. Besides, pyridyl halides, alkyl halides and electron-deficient aryl chlorides that are challenging to reduce were also compatible with this reaction.

In the preliminary mechanistic study, the control experiments without using aryl halides could afforded a decarboxylation product, suggesting that a highly reductive CO₂ radical anion might be involved in this reaction to reduce aryl halides to generate aryl radicals. When a “radical clock” substrate was used, ring-opening product was produced, indicating a benzyl radical might be involved. Besides, the reaction could be scalable without significant decrease in the yield of desired products.

This study may provide a new opportunity for exploring novel visible-light-driven Meerwein-type arylation-addition reactions employing user-friendly aryl halides as the radical sources, as well as developing new photocatalytic utilization reactions of CO₂.

Figure: Visible-light-driven arylcarboxylation of styrenes with CO₂ and aryl halides. (Image by Prof. LI’s group)