Synthesis

Blue Light-Mediated Decarboxylative Coupling Transforms Carboxylic Acid Feedstocks

Context

Carboxylic acids are among the most abundant and inexpensive organic building blocks, available from biomass and petrochemical sources. However, their use in synthesis often requires wasteful activation steps (e.g., conversion to acid chlorides) and generates stoichiometric byproducts. Direct decarboxylative functionalization—removing CO₂ and forming new C-C bonds—offers an attractive alternative but typically requires specialized reagents or harsh conditions.

What's New

The research demonstrates that a simple organic photocatalyst (dicyanobenzene) under blue LED irradiation can mediate decarboxylative radical generation from carboxylic acids, which then add to electron-deficient alkenes. The protocol uses only catalytic photocatalyst (2 mol%) and inexpensive persulfate oxidant in aqueous acetonitrile at room temperature. Substrate scope includes amino acids, aliphatic acids, and aromatic acids, delivering coupled products in good yields.

Why It Matters

This operationally simple methodology makes decarboxylative coupling accessible to non-specialist laboratories and could find applications in late-stage functionalization of complex molecules. The use of blue LEDs (widely available, efficient) and near-ambient conditions aligns with green chemistry principles. Potential applications include biomass valorization and streamlined synthesis of pharmaceuticals and agrochemicals.

Limitations & Open Questions

The reaction currently requires superstoichiometric persulfate oxidant, generating sulfate waste. Highly electron-rich alkenes give poor yields. Scale-up demonstrations are limited to 1-5 mmol. The system shows sensitivity to oxygen and moisture, requiring careful technique. Extension to other radical acceptors (e.g., alkynes, arenes) requires additional development.
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References

Angewandte Chemie International Edition (2023)

DOI: 10.1002/anie.202301234

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