CON(C)[C:4]([C@@H:6]1[CH2:10][C@H:9]([CH3:11])[CH2:8][N:7]1[C:12]([O:14][C:15]([CH3:18])([CH3:17])[CH3:16])=[O:13])=[O:5].[H-].[Al+3].[Li+].[H-].[H-].[H-]>C1COCC1>[CH:4]([C@@H:6]1[CH2:10][C@H:9]([CH3:11])[CH2:8][N:7]1[C:12]([O:14][C:15]([CH3:16])([CH3:18])[CH3:17])=[O:13])=[O:5](2S,4S)-tert-butyl 2-(methoxy(methyl)carbamoyl)-4-methylpyrrolidine-1-carboxylate (5.30 g, 19.5 mmol) was dissolved in 120 mL THF, cooled to −78° C. and treated with lithium aluminum hydride (1M in THF, 19.5 mL, 19.5 mmol) dropwise via addition funnel. After 1 hour, the mixture was brought to 0° C. and kept at that temperature for 2 hours. It was quenched by dropwise addition of a 50 mL solution of 3.0 g KHSO4 in water, removed from the ice bath, and stirred 15 minutes at room temperature. The product was extracted with three 75 mL portions of ethyl acetate and washed with brine. The organic phase was dried over sodium sulphate, filtered, and concentrated to give crude (2S,4S)-tert-butyl 2-formyl-4-methylpyrrolidine-1-carboxylate. (4.89 g)
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