Hydrochloric Acid → 2,3-Dihydroxy-4-methoxybenzaldehyde

2,3,4-trimethoxybenzaldehyde, 1 (9.8 g, 50 mmol) was dissolved in anhydrous dichloromethane (150 ml) under argon at ambient temperature. It was stirred for 10 minutes and boron trichloride (100 ml, 100 mmol, 2 eq; 1.0M solution in dichloromethane) was added. The dark reaction mixture was stirred for 24 hours and then slowly poured into 10% sodium bicarbonate (aq) (40 g/360 ml). The resulting solution was acidified with concentrated hydrochloric acid to pH 1. The dichloromethane layer was separated and the aqueous layer was extracted with ethyl acetate (4×100 ml) and dried. Evaporation of the solvent in vacuo gave a brown oil which was absorbed onto silica gel and subjected to flash chromatography (70:30, hexane-ethyl acetate). The diol 2 was obtained as a pale yellow solid (6.70 g, 80%).