反应详情

(R)-3-(Benzyloxycarbonylamino)-4-hydroxybutanoic acid (INTERMEDIATE 2, 27.7 g, 109.38 mmol) was dissolved in toluene (648 ml). p-Toluenesulfonic acid (367 mg, 2.13 mmol) was added to the solution and the resulting mixture was heated at reflux under Dean-Stark conditions for 3 hours. The reaction mixture was cooled to room temperature and concentrated in vacuo. Diethyl ether (200 ml) was added, and formation of crystals was observed upon standing. The crystals were filtered in vacuo. The mother liquors were concentrated in vacuo and additional diethyl ether (40 ml) was added. More crystals appeared which were filtered in vacuo. Both sets of crystals combined to give the title product (22.8 g, yield: 83%).

1. temperaturethe resulting mixture was heated
2. temperatureat reflux under Dean-Stark conditions for 3 hours
3. concentrationconcentrated in vacuo
4. additionDiethyl ether (200 ml) was added
5. filtrationThe crystals were filtered in vacuo
6. concentrationThe mother liquors were concentrated in vacuo and additional diethyl ether (40 ml)
7. additionwas added
8. filtrationwere filtered in vacuo