[C:1]([C@@H:3]1[CH2:7][N:6]([C:8]([O:10][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:9])[C@H:5]([C:15]([O:17][CH3:18])=[O:16])[CH2:4]1)#N.Cl.[C:20](OC(OC(C)(C)C)=O)(OC(C)(C)C)=[O:21].C[OH:36]>>[N:6]1([C:8]([O:10][C:11]([CH3:14])([CH3:13])[CH3:12])=[O:9])[CH2:7][C@@H:3]([C:1]([O:21][CH3:20])=[O:36])[CH2:4][C@H:5]1[C:15]([O:17][CH3:18])=[O:16]To a solution of (2S,4S)-1-tert-butyl 2-methyl 4-cyanopyrrolidine-1,2-dicarboxylate (9.0 g, 35.4 mmol) in MeOH (196 mL) was added HCl (4M in 1,4-dioxane, 100 mL, 403 mmol). The solution was stirred at room temperature for 16 h and concentrated in vacuo. The crude intermediate was dissolved in EtOAc (180 mL) and basified with aqueous bicarbonate (sat.). Di-tert-butyl dicarbonate (8.5 g, 38.9 mmol) was added and the biphasic solution was stirred at room temperature for 12 h. The layers were then separated and the aqueous layer was backextracted with EtOAc. The combined organic layers were washed with brine, dried over Na2SO4, and concentrated. The crude oil was purified by silica gel chromatography (15% to 40% to 100% EtOAc/Hexanes) to provide (2S,4S)-1-tert-butyl 2,4-dimethyl pyrrolidine-1,2,4-tricarboxylate (9.56 g, 94%).
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