A solution of Intermediate 1a (250 mg) obtained in Example 1-1, Step A, 2,6-di(tert-butyl)-4-methylphenol (0.5 mg, Tokyo Kasei Kogyo), and tri(n-butyl)vinyltin (0.25 ml, Tokyo Kasei Kogyo) in toluene (8 ml) was added with tetrakis(triphenylphosphine)palladium(0) (13 mg, Kanto Chemicals) under a nitrogen gas atmosphere, and the mixture was refluxed by heating for 12 hours. The reaction mixture was cooled to room temperature, and then the solvent was evaporated under reduced pressure. The residue was purified by silica gel chromatography (n-hexane:ethyl acetate=2:1) to obtain the title compound (195 mg).
