Step 9a: Synthesis of ethyl 4-(benzyloxy)-3-hydroxybenzoate (compound 502)
A mixture of ethyl 3,4-dihydroxybenzoate (9.1 g, 50 mmol), benzyl chloride (6.3 g, 50 mmol), potassium iodide (1.66 g, 10 mmol) and potassium carbonate (13.8 g, 100 mmol) in acetonitrile (250 mL) was reacted by stirring at 40 °C overnight. Upon completion of the reaction, the mixture was cooled to room temperature and filtered. The filtrate was concentrated under reduced pressure and the residue was purified by silica gel column chromatography with petroleum ether/ethyl acetate (10:1, v/v) as eluent to give the title compound 502 as a white solid (4.4 g, 33% yield).
LCMS (m/z): 273 [M+1]+.
1H NMR (DMSO-d6): δ 9.49 (s, 1H), 7.35 (m, 7H), 7.08 (d, J = 7.8 Hz, 1H), 5.16 (s, 2H), 4.21 (m, 2H), 1.26 (t, J = 7.5 Hz, 3H).
