General procedure for the synthesis of 2,5-dimethyl-4-hydroxybenzaldehyde from 2,5-dimethyl-p-anisaldehyde:
Step A: 4-methoxy-2,5-dimethylbenzaldehyde (1.24 g, 7.55 mmol) was dissolved in anhydrous dichloromethane (12 mL). Pure boron tribromide (1.75 g, 18.5 mmol) was added slowly and dropwise under stirring conditions. Formation of a tan colored precipitate was observed during the reaction. The resulting suspension was stirred continuously at room temperature for 5 days. After completion of the reaction, the homogeneous reaction mixture was carefully poured into ice (150 g). After complete melting of the ice, the solid product 2,5-dimethyl-4-hydroxybenzaldehyde was isolated by filtration and dried to give 1.28 g of product (quantitative yield).
Product characterization data: 1H-NMR (400 MHz, DMSO-d6) δ= 10.40 (s, 1H), 9.98 (s, 1H), 7.54 (s, 1H), 6.68 (s, 1H), 3.36 (s, 1H), 2.49 (s, 3H), 2.13 (s, 3H).
