C(N(S(F)(F)[F:7])CC)C.[C:10]([O:14][C:15]([N:17]1[CH2:22][CH2:21][C:20]([CH2:24][C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)(O)[CH2:19][CH2:18]1)=[O:16])([CH3:13])([CH3:12])[CH3:11].O.C(=O)([O-])[O-].[K+].[K+]>ClCCl>[C:10]([O:14][C:15]([N:17]1[CH2:22][CH2:21][C:20]([CH2:24][C:25]2[CH:30]=[CH:29][CH:28]=[CH:27][CH:26]=2)([F:7])[CH2:19][CH2:18]1)=[O:16])([CH3:13])([CH3:12])[CH3:11]To a cooled (-71° C.) and stirred solution of diethylaminosulfur trifluoride (634 μl, 4.80 mmol) in anhydrous dichloromethane (15 ml) was added dropwise, via cannula, a solution of 1-tert-butyloxycarbonyl-4-benzyl-4-hydroxypiperidine (700 mg, 2.40 mmol) in anhydrous dichloromethane (15 ml) over 20 minutes, under nitrogen. After a further 50 minutes at -75° C., the mixture was warmed to -10° C. and stirred for a further 2 hours. Water (20 ml) and saturated aqueous potassium carbonate (7 ml) were added and products were extracted with diethyl ether (1×70 ml). The organic solution was washed with brine (1×25 ml), dried (MgSO4) and concentrated. Flash chromatography of the residue (silica gel, hexane-diethyl ether, 86:14) gave 190 mg of 1-tert-butyloxycarbonyl-3,4-dehydro-4-benzylpiperidine and 360 mg (51%) of the title compound as pale yellow oils; δH (360 MHz, CDCl3) 1.44 (9H, s), 1.46-1.78 (4H, m), 2.90 (2H, d, J=22 Hz), 2.98-3.08 (2H, m), 3.86-3.94 (2H, m), 7.16-7.34 (5H, m); m/z (ES) 294 (M+ 1).
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