Trifluoroacetic anhydride → (1R,5S)-6,6-Dimethyl-3-oxabicyclo(3.1.0)hexane-2,4-dione

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Reaction Steps

To a solution containing the product (caronic acid) of step 1 (10 g) in toluene (35 mL) was added trifluoroacetic anhydride (17.9 mL) over 10 min. The mixture was heated to reflux while simultaneously distilling out trifluoroacetic acid and excess trifluoroacetic anhydride. When the temperature reached 100-110° C., additional toluene (20 mL) was added and the reaction mixture was heated under reflux. After 3 h, the mixture was concentrated to about 30 mL. Toluene (70 mL) was added and the mixture once again concentrated to about 30 mL. This solution which contained the compound of formula II (assayed by 1H NMR using ρ-nitromethylbenzoate as an internal std) was used in the first step of Example 2 without further purification. Alternatively, the compound formula II can be purified by methods such as fractional distillation.

Provenance & Evidence