[C:1](Cl)(=[O:5])[C:2](Cl)=O.CS(C)=[O:9].O[CH2:12][CH:13]1[CH2:18][CH2:17][N:16]([C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])[CH2:15][CH2:14]1.C(N([CH2:31][CH3:32])CC)C>O1CCCC1.O>[CH2:31]([O:9][C:1](/[CH:2]=[CH:12]/[CH:13]1[CH2:18][CH2:17][N:16]([C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])[CH2:15][CH2:14]1)=[O:5])[CH3:32]To a solution of 10.7 g (84.4 mM) of oxalyl chloride in 100 ml of tetrahydrofuran was added 12.0 ml (169 mM) of dimethyl sulfoxide dropwise at −78° C. and the mixture was stirred for 5 minutes. Then, a solution of [ ]g ( mM) of tert-butyl 4-(hydroxymethyl)piperidine-1-carboxylate in 100 ml of tetrahydrofuran was added dropwise and the mixture was stirred at −78° C. for 15 minutes. To this mixture was added 47.0 ml (338 mM) of triethylamine at −78° C. and the temperature was increased to room temperature. This reaction mixture was poured in water and extracted with 3 portions of ethyl acetate. The organic layers were pooled and dried over MgSO4 and the solvent was distilled off under reduced pressure. The resulting crude tert-butyl 4-formylpiperidine-1-carboxylate was not purified but used as it was in the next reaction.
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