Hydrochloric Acid → 6-Bromo-3,4-dihydro-2H-1-benzopyran-4-ol

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Reaction Steps

To a suspension of 7-bromo-3,4-dihydronaphthalen-1(2H)-one (3.95 kg, 17.4 mol) in ethanol (20 L) at room temperature add sodium borohydride (221 g, 5.84 mol) in portions over 3 hr. Concentrate the clear red solution. Add the residue into ice (about 3 kg) to form a suspension and then slowly add ice-cooled 0.5 M HCl (10 L) into the above suspension with stirring. Extract the mixture with methyl tert-butyl ether (20 L and 5 L). Wash the combined organic phase with saturated aqueous sodium bicarbonate (10 L) and brine (2×10 L), concentrate the solvent under reduced pressure and dry the wet solid in air overnight to obtain the title compound as a pale yellow solid (4.10 kg, quantitative). LC-ES/MS m/z 211 [M−H-2O+H]+.

Provenance & Evidence