Improved preparation and characterization of unsaturated γ‐lactones

Abstract

Improved, high yield procedures for the preparation of unsaturated γ‐lactones (I‐IV) from saturated γ‐lactones (V) are described. Compounds V are first converted to the sodium salts of the corresponding γ‐hydroxy acids (VI) (100%) which are oxidized within fifteen minutes to the γ‐keto acids (VII) (75–85%) by bromine at pH 6‐7.5. Acid‐catalyzed reaction of VII with acetic anhydride at room temperature for fifteen minutes yields γ‐acetoxy‐γ‐lactones (VIII) (70–90%). Pyrolysis of VIII at 200–330° yields I‐IV (70–95%), the composition of which depends on whether strongly acidic contaminants have been completely removed from VIII prior to pyrolysis. In selected cases studied, fractional distillation permits the isolation of pure unsaturated lactones. Nmr has been extensively used to determine purity at each step and the composition of mixtures of I‐IV.

Efficient, solvent-free hydrogenation of α-angelica lactone catalysed by Ru/C at atmospheric pressure and room temperature

“…This suggests that the lactone composition equilibrates over time and an apparent equilibrium is reached after 5 h with 79 : 16 : 4 for a-AL, b-AL and g-MBL respectively. 13,[28][29][30][31] This is in good agreement with the equilibrium composition calculated by DFT (see ESI †). Besides lactone isomers, LA was also formed with up to 2%, which suggests the presence of some water in a-AL.…”