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7.42 g (0.02 mol) of N-benzyloxycarbonyl-L-tyrosine tert-butyl ester were refluxed for 6 h together with 9.77 g(0.03 mol) of cesium carbonate and 3.9 g (0.02 mol) of ethyl 4-bromo-butyrate in about 60 ml of acetone. After cooling the reaction mixture, the solvent was removed in vacuo. The residue was partitioned between ethyl acetate and water (1/1). After separation of the phases, the organic phase was washed two times each with water and saturated sodium chloride solution, dried over sodium sulfate and concentrated in vacuo. The oily crude product was purified by flash chromatography on silica gel (dichloromethane/acetonitrile 25/1). Yield: 9.4 g (97%) of viscous oil. Rf=0.36 (silica gel, dichloromethane/methanol 9911).

1. temperatureAfter cooling the reaction mixture
2. customthe solvent was removed in vacuo
3. customThe residue was partitioned between ethyl acetate and water (1/1)
4. customAfter separation of the phases
5. washthe organic phase was washed two times each with water and saturated sodium chloride solution
6. dry with materialdried over sodium sulfate
7. concentrationconcentrated in vacuo
8. customThe oily crude product was purified by flash chromatography on silica gel (dichloromethane/acetonitrile 25/1)