Yield: 99%

Reaction Conditions:

Stage #1:4-cyano-4-methoxytetrahydropyran with water;potassium hydroxide for 4 h;Reflux;
Stage #2: with hydrogenchloride;water

Steps:

182.2
Step 2 4-Methoxytetrahydropyran-4-carbonitrile (3.30 g, 232.2 mmol) obtained in the above was dissolved in water (30 mL), and potassium hydroxide (9.90 g, 177 mmol) was added thereto, and then, the mixture was stirred under reflux for 4 hours. The mixture was left to cool to room temperature, and then washed with diethyl ether. To the aqueous layer, concentrated hydrochloric acid (20 mL) was added, and the mixture was extracted with chloroform-isopropanol (6/1). The organic layer was dried over anhydrous magnesium sulfate, and the solvent was evaporated under reduced pressure to give a roughly purified product of 4-methoxytetrahydropyran-4-carboxylic acid (3.73 g, 23.2 mmol, yield: 99%). This roughly purified product was used in the subsequent step as such.

References:

Kyowa Hakko Kirin Co., Ltd. EP2090570, 2009, A1 Location in patent:Page/Page column 95