440122-66-7

67-56-1

440123-20-6

440122-66-7

Step e) Route for the synthesis of 7-bromo-2-(4-hydroxyphenyl)-1,3-benzoxazol-5-ol a) The operation was as follows: boron tribromide (1M, 89.9 mL, 89.8 mmol) was added dropwise to a mixture of 7-bromo-5-methoxy-2-(4-methoxyphenyl)-1,3-benzoxazolol (10.0 g, 29.94 mmol) in suspension at -70 °C with dichloromethane (50 mL) in suspension. The reaction mixture was gradually warmed up to room temperature, during which the suspension transformed into a black solution. After continuous stirring of the reaction mixture for 2 days at room temperature, it was slowly poured into pre-cooled (0 °C) ether (1000 mL). Subsequently, methanol (200 mL) was slowly added to the above mixture over a period of 20 minutes. The mixture was poured into water (1.5 L) and the organic layer was separated, washed three times with water and dried with anhydrous magnesium sulfate. After concentration by evaporation, the product was crystallized from a mixed solvent of acetone/ether/hexane to give an off-white solid product (8.4 g, 92% yield, melting point 298-299 °C); mass spectrometry analysis showed m/e 306 (M + H)+.