(4-Bromo-phenyl)-tert-butoxycarbonylamino-acetic acid benzyl ester (1.5 g, 3.6 mmol), methyl vinyl sulfone (406 μL, 4.6 mmol), palladium(II) acetate (80 mg, 10 mol %), tri-o-tolylphosphine (217 mg, 20 mol %) and triethylamine (2.0 ml, 14.3 mmol) were combined in acetonitrile (18 mL), degassed and refluxed for 8 hours. Additional palladium(II) acetate (80 mg, 10 mol %) and tri-o-tolylphosphine (217 mg, 20 mol %) were added and refluxing continued overnight. The reaction was cooled, solvent removed in vacuo and the residue was purified by chromatography over silica gel gradient eluted from 20 to 90% v/v ethyl acetate in hexane to afford tert-butoxycarbonylamino-[4-((E)-2-methanesulfonyl-vinyl)-phenyl]-acetic acid benzyl ester (1.2 g, 75%).
