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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.

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Aus den Lactonen (I) erhält man durch Hydrolyse unter alkalischen Bedingungen die Carboxylate (II), die mit Brom bei pH 6 ‐ 7,5 zu den Ketonen (III) oxidiert werden.

Da die direkte Monochlorierung von Parabansäure nicht zu reproduzierbaren Ergebnissen führt, wird Monochlorparabansäure (I) durch Umsetzung von Dichlorparabansäure und Parabansäure in Aceton bei 0°C erhalten.