A solution of tert-butyl 4-[(6-hydroxy-3-oxo-2,3-dihydrobenzofuran-7-yl)methyl]piperazine-1-carboxylate (0.400 g, 1.15 mmol) obtained in Example A16, Step 1, methanol (0.0442 g, 1.38 mmol) and triphenylphosphine (0.454 g, 1.73 mmol) in THF (8 mL) was added with a solution of a 40% solution of diethyl azodicarboxylate in toluene (0.901 g, 2.07 mmol) in THF (2 mL), and the mixture was stirred overnight at room temperature. The reaction mixture was concentrated, and the resulting residue was purified by silica gel column chromatography (chloroform/ethyl acetate) to obtain tert-butyl 4-[(6-methoxy-3-oxo-2,3-dihydrobenzofuran-7-yl)methyl]piperazine-1-carboxylate (0.107 g, 25%).
