[O:1]=[C:2](N1CCOC1=O)[CH2:3][CH2:4][CH:5]=O.[CH3:13][C:14]1([NH2:24])[CH2:23][CH2:22][C:17]2([O:21][CH2:20][CH2:19][O:18]2)[CH2:16][CH2:15]1.C(O)(=O)C.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>ClCCCl.O>[CH3:13][C:14]1([N:24]2[CH2:5][CH2:4][CH2:3][C:2]2=[O:1])[CH2:23][CH2:22][C:17]2([O:18][CH2:19][CH2:20][O:21]2)[CH2:16][CH2:15]1Dissolve 4-oxo-4-(2-oxo-oxazolidin-3-yl)-butyraldehyde (7.35 g, 42.96 mmol) in DCE (400 mL). Add 8-methyl-1,4-dioxa-spiro[4.5]dec-8-ylamine (7.36 g, 42.96 mmol), and acetic acid (2.58 g, 42.96 mmol) at room temperature under nitrogen. Stir the solution for one hour and then add sodium triacetoxyborohydride (18.21 g, 85.92 mmol). Stir the reaction mixture for over night and then add water (400 mL). Extract the aqueous layer with dichloromethane (3×400 mL). Combine the organic layers and dry with Na2SO4, filter, concentrate and purify by flash column chromatography (silica gel, 20-50% of EtOAc-Hexane) to give 0.92 g (9.0%) of 1-(8-Methyl-1,4-dioxa-spiro[4.5]dec-8-yl)-pyrrolidin-2-one as a colorless oil.
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