Azodicarboxylic dipiperidide (0.756 g, 3.0 mmol) was added at 0-5°C. to a stirred solution of tributylphosphine (0.74 ml, 0.61 g, 3.0 mmol), (S)-ethyl 2-ethoxy-3-(4-hydroxyphenyl)-propionate (0.500 g, 2.10 mmol) and (E)-3-(4-bromophenyl)-but-2-en-1-ol (0.454 g, 2.0 mmol) in dry benzene (20 ml), the mixture warmed to room temperature, and stirred for 2.5 days. The resulting mixture was diluted with water and ethyl acetate (50 ml each), the aqueous layer collected and further extracted with ethyl acetate (50 ml). The organic layers were combined, washed with brine, dried (MgSO4) and evaporated. The crude product was then purified by column chromatography on silica gel (20% ethyl acetate in n-heptane eluent) to give (E)-(S)-ethyl 3-{4-[3-(4-bromophenyl)-but-2-enyloxy]-phenyl}-2-ethoxy-propionate as an oil; 0.780 g (87%).
