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4-Oxo-4,5,6,7-tetrahydrobenzofuran-3-carboxylic acid is prepared according to the following procedure. Potassium hydroxide (345 g, 6.15 mol) is dissolved in methyl alcohol (1.2 L) then cooled in an ice water bath. A solution of cyclohexanedione (714 g, 6.15 mol) in methyl alcohol (1.2 L), dissolved using gentle heat, is added dropwise to the cold, stirred KOH solution over 2 h. A solution of ethyl bromopyruvate (1200 g, 6.15 mol) in methyl alcohol (1.5 L) is then added dropwise over 3 h. The reaction mixture is allowed to reach ambient temperature and stirred an additional 14.5 h. While cooling the reaction mixture via a water bath, a solution of sodium hydroxide (492 g, 12.4 mol) in water (984 mL) is added dropwise over 2.5 h. After stirring at ambient temperature for 15.5 h, the reaction mixture is cooled in an ice water bath, 500 g of ice added, and the resulting mixture is then acidified with concentrated hydrochloric acid (ca 1 L) to pH 1. The reaction mixture is concentrated in vacuo, 1 L of ice is added, and the precipitate filtered, washed with ice water (3×200 mL), and then dried in a vacuum oven at 75° C. to afford 4-oxo-4,5,6,7-tetrahydrobenzofuran-3-carboxylic acid (560 g). m.p. 137-138° C.

1. custom4-Oxo-4,5,6,7-tetrahydrobenzofuran-3-carboxylic acid is prepared
2. temperaturethen cooled in an ice water bath
3. additionis added dropwise to the cold
4. customto reach ambient temperature
5. temperatureWhile cooling the reaction mixture via a water bath
6. stirringAfter stirring at ambient temperature for 15.5 h
7. temperaturethe reaction mixture is cooled in an ice water bath
8. concentrationThe reaction mixture is concentrated in vacuo, 1 L of ice
9. additionis added
10. filtrationthe precipitate filtered
11. washwashed with ice water (3×200 mL)
12. customdried in a vacuum oven at 75° C.