[C:1]([O:5][C:6]([N:8]1[CH2:12][CH2:11][CH2:10][C@H:9]1[CH:13]=O)=[O:7])([CH3:4])([CH3:3])[CH3:2].[CH:15]1([NH2:18])[CH2:17][CH2:16]1.[BH4-].[Na+].O>CO.CC(C)[O-].[Ti+4].CC(C)[O-].CC(C)[O-].CC(C)[O-]>[CH:15]1([NH:18][CH2:13][C@@H:9]2[CH2:10][CH2:11][CH2:12][N:8]2[C:6]([O:5][C:1]([CH3:4])([CH3:3])[CH3:2])=[O:7])[CH2:17][CH2:16]1
3.78 mL (13 mmol) of titanium isopropoxide and 2 g (10 mmol) of (S)-1-tert-butoxycarbonyl-pyrrolidine-2-carbaldehyde are added to a solution of 1.7 mL (30 mmol) of cyclopropylamine in 10 mL of anhydrous methanol. The solution is stirred for 5 hours at room temperature then 378 mg (10 mmol) of sodium borohydride is added. Stirring is continued for a further 2 hours then 2 mL of water is added. The reaction mixture is filtered then the solvents are evaporated. Water is added and the compound is extracted with diethyl ether. The organic phases are dried over magnesium sulfate, filtered and evaporated to give 2.34 g (97%) of (S)—N-cyclopropyl-1-tert-butoxycarbonyl-pyrrolidin-2-ylmethyl-amine in the form of a colourless oil.
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