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In a flask made of glass equipped with a stirring device, a thermometer and a dropping funnel and having an inner volume of 50 ml were charged the above-mentioned tetrahydropyran-4,4-dicarboxylic acid, 17.6 ml of pyridine and 123.1 mg (0.86 mmol) of copper(I) oxide, and the mixture was subjected to decarboxylation under nitrogen atmosphere at 110 to 120 C. for 1 hour. After completion of the reaction, the mixture was cooled to room temperature, 30 ml of water, 30 ml (360 mmol) of conc. hydrochloric acid and 60 ml of ethyl acetate were successively added in this order, and the aqueous layer and the organic layer were separated. After the aqueous layer was washed three times with each 60 ml of ethyl acetate, these extracts and the organic layer were combined and concentrated under reduced pressure to give 3.15 g (Isolation yield: 24.2%) of tetrahydropyran-4-carboxylic acid with purity of 100% (analytical value by differential refractometry) as white crystals.

1. customIn a flask made of glass
2. customequipped with a stirring device
3. customAfter completion of the reaction
4. customthe aqueous layer and the organic layer were separated
5. washAfter the aqueous layer was washed three times with each 60 ml of ethyl acetate
6. concentrationconcentrated under reduced pressure