Chromocarb → 3,4-dihydro-2H-1-benzopyran-2-carboxylic acid

Participants

Reaction Steps

A mixture of 4-oxochromene-2-carboxylic acid (20.0 g, 105 mmol) and Pd/C (3.0 g, w/w=10%) in AcOH (200 mL) was placed in Parr hydrogenation apparatus under H2 (50 psi) and stirred for 25 h at rt. It was then filtered and concentrated. The residue was suspended in water (300 mL), stirred for 10 min, filtered and dried to give 3,4-dihydro-2H-chromene-2-carboxylic acid (13.5 g, 72%) as a white solid. BH3 (57 mL, 114 mmol, 2.0 M in THF) was added slowly to a solution of this carboxylic acid in THF (120 mL) at 0° C. The reaction mixture was then warmed to rt and stirred for 5 h at this temperature. THF/H2O (30 mL, 1:1) was added drop wise while keeping the temperature between 0-5° C. and stirred for 20 min. K2CO3 (26.0 g, 189 mmol) was added and the reaction was vigorously stirred for 30 min. The THF layer was separated and concentrated to give the title compound (11.0 g, 89%) as a brown oil. 1H NMR (400 MHz, CDCl3): δ 7.10-7.03 (m, 2H), 6.86-6.81 (m, 2H), 4.14-4.08 (m, 1H), 3.85-3.68 (m, 2H), 2.92-2.84 (m, 1H), 2.80-2.73 (m, 1H), 1.98-1.92 (m, 1H), 1.90-1.79 (m, 1H). LCMS: 165 (M+1)+

Provenance & Evidence