To a ice-cooled solution of (4-methanesulfonylamino-2-methoxy-5-vinyl-benzyl)-carbamic acid tert-butyl ester (220 mg, 0.73 mmol) in methylene chloride was treated with trifluoroacetic acid (100 mg, 0.88 mmol)) for 1 hr, and then concentrated under reduced pressure. The part of crude residue (100 mg, 0.27 mmol) was suspended in methylene chloride and treated with triethylamine followed by (4-tert-butyl-benzyl)-carbamic acid phenyl ester (92 mg, 0.32 mmol). The resulting mixture was heated with reflux for 3 days and concentrated under reduced pressure. The crude residue was column-chromatographed (hexane/ethylacetate=1/2) to yield a white solid (8.8 mg, 7.0%).
