FC(F)(F)C(O)=O.[CH3:8][O:9][C:10]([C@@H:12]1[CH2:16][C@H:15]([N:17]=[N+:18]=[N-:19])[CH2:14][NH:13]1)=[O:11].[CH:20]1([CH:26]=O)[CH2:25][CH2:24][CH2:23][CH2:22][CH2:21]1.C(O)(=O)C.C(O[BH-](OC(=O)C)OC(=O)C)(=O)C.[Na+]>ClCCl>[CH3:8][O:9][C:10]([C@@H:12]1[CH2:16][C@H:15]([N:17]=[N+:18]=[N-:19])[CH2:14][N:13]1[CH2:26][CH:20]1[CH2:25][CH2:24][CH2:23][CH2:22][CH2:21]1)=[O:11]To a solution of (2S,4S)-4-azido-pyrrolidine-2-carboxylic acid methyl ester trifluoroacetate salt (9.6 g, 33.08 mmol) in 60 mL dichloromethane were added cyclohexanecarbaldehyde (2.6 g, 23.66 mmol), acetic acid (2.5 mL) and sodium triacetoxyborohydride (14.2 g, 66.16 mmol) and the reaction mixture was stirred at room temp. for 20 h. The reaction mixture was diluted with dichloromethane, washed with water, dried over anhydrous sodium sulfate and concentrated to give (2S,4S)-4-azido-1-cyclohexylmethyl-pyrrolidine-2-carboxylic acid methyl ester (11.2 g, crude) as a light brown liquid. The compound was used in the next step without further purification. MS calcd. for C13H23N4O2 [(M+H)+] 267.0, obsd. 267.2.
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