CS(C)=O.C(Cl)(=O)C(Cl)=O.[OH:11][CH2:12][C@@H:13]1[CH2:18][CH2:17][CH2:16][N:15]([C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])[CH2:14]1.C(N(CC)CC)C>ClCCl.[Cl-].[Na+].O>[CH:12]([C@@H:13]1[CH2:18][CH2:17][CH2:16][N:15]([C:19]([O:21][C:22]([CH3:25])([CH3:24])[CH3:23])=[O:20])[CH2:14]1)=[O:11]
DMSO (3.3 ml, 46.6 mmol, 2.2 eq) in dichloromethane (20 ml) is added dropwise to a solution of oxalyl chloride (2.03 ml, 23.2 mmol, 1.1 eq) in dichloromethane (80 ml) cooled to −78° C. This mixture is stirred for 10 mins and then tert-butyl (3R)-3-(hydroxymethyl)piperidine-1-carboxylate (4.56 g, 21.1 mmol, 1 eq) in dichloromethane (20 ml) is added dropwise. This is stirred for 20 mins and then triethylamine (15.0 ml, 105 mmol, 5 eq) is added in one portion and then warmed to room temperature over 30 mins. The solution is poured onto diethyl ether (300 ml) and brine (300 ml), separated and the aqueous layer is extracted with diethyl ether (2×100 ml). The organic layers are combined, washed with brine (100 ml), dried over magnesium sulphate, filtered and concentrated in vacuo to give tert-butyl (3R)-3-formylpiperidine-1-carboxylate (4.33 g, 96%) 1H NMR (300 MHz, CDCl3) δH 9.63 (1H, s), 3.75-3.98 (1H, m), 3.48-3.66 (1H, m), 3.16-3.34 (1H, m), 2.90-3.11 (1H, m), 2.26-2.44 (1H, m), 1.79-1.97 (1H, m), 1.53-1.70 (2H, m) and 1.20-1.49 (10H, m).
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