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(Buckley III, T. F.; Rapoport, H. J. Org. Chem. 1984, 48, 4222) Concentrated sulfuric acid (11 mL) was added to a suspension of d,l-glutamic acid (0.17 mol, 25 g) in 2-propanol/toluene (675 mL, 1/1). The solution was refluxed for 24 hours using a Soxhlet apparatus containing 3 Å molecular sieves, and then evaporated to approximately 100 mL. The residue was diluted with cold saturated NaHCO3 (300 mL), adjusted to pH 9.5 and extracted with CH2Cl2 (4×150 mL). The combined extracts were dried over Na2SO4 and concentrated in vacuo to give diisopropyl glutamate as an oil (38.6 g): 1H NMR (Buckley III, T. F.; Rapoport, H. J. Org. Chem. 1984, 48, 4222) (300 MHz) δ 5.04 (heptet, J=6.3 Hz, 1 H), 5.01 (heptet, J=6.3 Hz, 1 H), 3.41 (dd, J=8.6, 5.3 Hz, 1 H), 2.42 (t, J=7.7 Hz, 2 H), 2.05 (m, 1 H), 1.82 (m, 1 H), 1.26 (d, J=6.3 Hz, 6 H), 1.23 (d, J=6.3 Hz, 6 H); 13C NMR (75 MHz) δ 175.14, 172.67, 68.47, 67.72, 53.87, 31.00, 29.84, 21.78.

1. temperatureThe solution was refluxed for 24 hours
2. additioncontaining 3 Å molecular sieves
3. customevaporated to approximately 100 mL
4. additionThe residue was diluted with cold saturated NaHCO3 (300 mL)
5. extractionextracted with CH2Cl2 (4×150 mL)
6. dry with materialThe combined extracts were dried over Na2SO4
7. concentrationconcentrated in vacuo