Cl.C(N=C=NCCCN(C)C)C.[C:13]([N:20]1[CH2:27][CH2:26][CH2:25][C@@H:21]1C(O)=O)([O:15][C:16]([CH3:19])([CH3:18])[CH3:17])=[O:14].ClC1C=C(C=CC=1Cl)CN1CCNCC1>C(Cl)Cl>[C:16]([O:15][C:13]([N:20]1[CH2:27][CH2:26][CH2:25][CH2:21]1)=[O:14])([CH3:19])([CH3:17])[CH3:18]1-Ethyl-3-(3′-dimethylaminopropyl)carbodiimide hydrochloride (1.03 g, 7 mmol) was added to absolution of N-BOC-D-Proline (1.51 g, 7 mmol) in methylene chloride (12 ml) and the reaction mixture was stirred at room temperature. After 0.5 h, 3,4-dichlorobenzylpiperazine (1.32 g, 5.4 mmol) [prepared as described in Example 1] was added and the stirring was continued for 16 h. The reaction mixture was then quenched with water, basified with saturated sodium bicarbonate solution and extracted with ethyl acetate. The ethyl acetate layer was separated and washed with brine, dried over magnesium sulfate and concentrated. Flash chromatography with 30% acetone in dichloromethane as the eluant gave 2(R)-[4-(3,4-dichlorobenzyl)piperazin-1-ylcarbonyl]}-N-(tert-butoxycarbonyl)pyrrolidine (1.2 g) as an oil.
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