[CH3:1][O:2][C:3]([C@H:5]1[CH2:10][CH2:9][C@@H:8]([C:11]([O:13][CH3:14])=[O:12])[CH2:7][NH:6]1)=[O:4].[CH3:15][S:16](Cl)(=[O:18])=[O:17]>ClCCl.CN(C)C1C=CN=CC=1>[CH3:1][O:2][C:3]([CH:5]1[CH2:10][CH2:9][CH:8]([C:11]([O:13][CH3:14])=[O:12])[CH2:7][N:6]1[S:16]([CH3:15])(=[O:18])=[O:17])=[O:4]6-ring: To rac-cis-Piperidine-2,5-dicarboxylic acid dimethyl ester [Frank J., J. Heterocyclic Chem. 32, 857–861 (1995)] (36.2 g) dissolved in dichloromethane (720 ml) were added 4-dimethylaminopyridine (33.0 g) and, dropwise, methanesulphonyl chloride (28.6 g) within 10 minutes and room temperature. The temperature rose to 35° C. The reaction mixture was stirred 1 h at room temperature, washed with 2 molar HCl, sodium carbonate-solution and brine, dried over magnesium sulphate and concentrated to dryness to obtain (2RS,5RS)-1-methanesulfonyl-piperidine-2,5-dicarboxylic acid dimethyl ester (46.8 g) as a syrup, MS: 220 (M+-59).
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