70 mg (0.18 mmol) of the compound obtained in Step 3 was dissolved in 1.5 ml of methylene chloride, and 57 mg (0.27 mmol) of NaBH(OAc)3 and 30 μl (0.40 mmol) of formaldehyde were added thereto. After stirring at room temperature for 22 hours, the reaction mixture was treated with a saturated sodium bicarbonate aqueous solution, and the water layer was separated and extracted twice with 10 ml of methylene chloride. The organic layers were combined, dried over anhydrous MgSO4, and concentrated under a reduced pressure. The residue was subjected to column chromatography using 20% ethyl acetate/hexane as an eluent to obtain 50 mg (yield 73%) of (E)-methyl-2-[2-((4-(N-isobutyl-N-methylamino)-2-fluorophenoxy)methyl)phenyl]-3-methoxyacrylate as an oil.
