Oxidative cyclization of ω-carboxyalkyl radicals to lactones

Conclusions

• 1. ω-Carboxyalkyl radicals HOOC(CH₂)_nCH₂, where n=4–7, were generated by the oxidative decarboxylation of pentane-, hexane-, heptane-, and octanedicarboxylic acids at 60°C in aqueous solution by the action of Na₂S₂O₈ in the presence of silver nitrate. The relation between the ability of these radicals to undergo oxidative cyclization to lactones and the number of methylene groups (n) and also the effect of copper ions on the oxidative cyclization process were investigated.

• 2. The main products from oxidative cyclization ofω-carboxyalkyl radicals in the absence of copper ions areγ-alkyl-γ-butyrolactones. In addition, alkanoic acids (84–95%) are formed as a result of abstraction of H atoms from the organic substrates by the radicals.

• 3. The main products from the oxidative cyclization of theω-carboxyalkyl radicals in the presence of copper ions areγ-alkyl-Δ^α,β-butenoiides.ω-Alkenoic acids (58–98%) are formed as a result of the oxidativeβ-deprotonation of the radicals by the action of Cu(II).