6-Fluorochromane-2-carboxylic acid

99199-59-4

99199-60-7

General procedure for the synthesis of 6-fluorobenzodihydropyran-2-carboxylic acid from 6-fluoro-4-oxo-4H-1-benzopyran-2-carboxylic acid: 30 g (0.144 mol) of 6-fluoro-4-oxo-4H-1-benzopyran-2-carboxylic acid, 5 g of wet palladium-carbon (5% Pd/carbon, 50% aqueous content) and 500 mL of glacial acetic acid were placed in an autoclave. After sealing three times under nitrogen protection, the nitrogen was replaced with hydrogen. Subsequently, the hydrogen was pressurized to 2.0 MPa and the reactor was heated to 7080°C. During the reaction, when the hydrogen pressure in the kettle dropped, the hydrogen was promptly replenished to 2.0 MPa. The reaction was considered to be completed when the reactor pressure remained stable and did not change any more within half an hour. After the reaction was completed, the hydrogen in the autoclave was released and the reaction solution was filtered to recover the Pd/C catalyst. The filtrate was concentrated under reduced pressure to recover glacial acetic acid. The remaining concentrate was poured into 30 mL of petroleum ether and heated to give a white crystalline solid. The solid was filtered and dried to give a final 25 g of white 6-fluorobenzodihydropyran-2-carboxylic acid solid in 88.4% yield and 99.8% purity.