To a solution of 5-(benzyloxy)-3-methyl-2-(propan-2-yloxy)pyridine-4-carboxylic acid (131a, 1.4 g, 4.7 mmol) in dry CH2Cl2 (50 mL) and dry MeOH (5 mL) was added dropwise TMSCHN2 (2.6 mL, 5.1 mmol, 2M in hexane) at 0° C. under N2. The reaction mixture was stirred at room temperature for 2 hours then concentrated under vacuum. The residue was purified by column chromatography (petroleum ether/EtOAc, 10/1) to give methyl 5-(benzyloxy)-3-methyl-2-(propan-2-yloxy)pyridine-4-carboxylate (131b, 1.1 g, 75%) as a colorless oil.
