Triethylamine → 3,4-Dihydro-1H-2-benzopyran-1-ol

Participants

Reaction Steps

To a stirred solution of crude product from step 5 (1.89 g; 5.49 mmol) in a mixture of acetone (80 ml) and water (25 ml) was added p-toluene sulfonic acid monohydrate (70 mg; 0.37 mmol). After stirring at room temperature for 3 hours, triethylamine (2 ml; 1.43 mmol) was added and stirred for 5 minutes. The mixture was evaporated until volume went down to 10 ml. A mixture of acetone (80 ml) and water (15 ml) was added followed by addition of p-toluene sulfonic acid monohydrate (70 mg; 0.37 mmol). After 3.5 hours, triethylamine (3 ml; 2.15 mmol) was added, evaporated to a small volume, extracted with ether (3×100 ml). The extract was washed with brine (50 ml), dried over MgSO4 and evaporated yielding quite pure 1-hydroxyisochroman (1.3 g; 94%), (MP. 136°-138° C.). NMR (CDCl3 ; 300 MHz) δ:2.32 (3H, s, CH3O), 2.51 (1H, dd, J=12.4, 17.5 Hz, H-4), 2.97 (1H, d, J=3.5 Hz; --OH), 3.06 (1H, dd, J=4.1, 17.5 Hz, H-4), 3.77, 3.82 (3H, s each, ArOCH3), 4.70 (1H, dd, J=4.1, 12.4 Hz, H-3), 6.22 (1H, d, J=3.4 Hz, 1H), 6.71, 6.76, (1H, d each, J=9.0 Hz, ArH).

Provenance & Evidence