IC.[C:3]([O:7][C:8]([NH:10][C@@H:11]([CH2:15][C:16]#[N:17])[C:12]([OH:14])=[O:13])=[O:9])([CH3:6])([CH3:5])[CH3:4].[CH2:18]1CCN2C(=NCCC2)CC1.OS([O-])(=O)=O.[K+]>C1(C)C=CC=CC=1.C(OCC)(=O)C.O>[CH3:18][O:13][C:12](=[O:14])[C@@H:11]([NH:10][C:8]([O:7][C:3]([CH3:6])([CH3:5])[CH3:4])=[O:9])[CH2:15][C:16]#[N:17]Iodomethane (2.18 ml, 35.01 mmol) was added to a mixture of (S)-2-(tert-butoxycarbonylamino)-3-cyanopropanoic acid (5.00 g, 23.34 mmol) and DBU (3.67 ml, 24.51 mmol) in toluene (20 mL) at rt. The reaction was stirred at 50 C for 2 days. Water (20 mL), saturated KHSO4 (20 mL) and ethyl acetate (50 mL) were added. The organic layer was separated, washed with brine and dried over sodium sulfate. After removal of solvent, the residue was purified by chromatography (hexane:Ethyl acetate=2:1) to give the (S)-methyl-2-(tert-butoxycarbonylamino)-3-cyanopropanoate as white solid (4.6 g, 86%). 1H NMR (400 MHz, d6-DMSO) δ7.64 (d, J=8.8 Hz, 1H), 4.39 (m, 1H), 3.66 (s, 3H), 2.96 (dd, J=16.8 Hz & 5.1 Hz, 1H), 2.85 (dd, J=16.8 Hz & 5.2 Hz, 1H), 1.40 (s, 9H).
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