反应详情

A solution of L-pyroglutamic acid (Aldrich, 25.0 g, 195 mmol) and para-toluenesulfonic acid mono hydrate (3.71 g, 19.5 mmol) was refluxed in isopropanol (40 mL) under nitrogen for 6 hours using a Dean-Stark trap variation (condensate returned through a Soxhlet extractor filled with 4 Å molecular sieves). After cooling to room temperature, the reaction was diluted with ether, washed with saturated aqueous sodium bicarbonate and then saturated aqueous NaCl, dried (MgSO4) and evaporated to give a colorless syrup. It crystallized upon setting. Triturating the crystalline residue in hexane provided 31.9 g (96%) of isopropyl pyrrolidin-5-one-2(S)-carboxylate as white prisms: 1H NMR (300 MHz, Chloroform-D) δ 6.35 (br s, 1 H), 5.04 (sept. 1H, J=6.2 Hz), 4.18 (dd, 1H, J=8.4, 5.3 Hz), 2.51-2.28 (m, 3H), 2.27-2.12 (m, 1H), 1.24 (d, 6H, J=6.2 Hz). LCMS m/z 172 (M+H)+.

1. additionfilled with 4 Å molecular sieves)
2. washwashed with saturated aqueous sodium bicarbonate
3. dry with materialsaturated aqueous NaCl, dried (MgSO4)
4. customevaporated
5. customto give a colorless syrup
6. customIt crystallized
7. customTriturating the crystalline residue in hexane