[CH2:1]([O:8][C:9](Cl)=[O:10])[C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1.O.Cl[CH:14](Cl)C.C(=O)(O)[O-].[Na+].C([N:24]([CH2:27][CH3:28])[CH2:25][CH3:26])C>C(OCC)(=O)C.C(Cl)(Cl)Cl.O.CC(C)=O>[C:9]([N:24]1[CH2:25][CH2:26][CH2:14][CH2:28][CH2:27]1)([O:8][CH2:1][C:2]1[CH:7]=[CH:6][CH:5]=[CH:4][CH:3]=1)=[O:10]The compound of formula XV is then treated with benzylchloroformate in a polar solvent such as water, water/acetone, chloroform, dichloroethane or ethyl acetate, in the presence of a base such as triethylamine or sodium bicarbonate, to yield the N-carbobenzyloxy piperidine (N--Cbz piperidine) of formula XVI having the same stereochemistry (i.e., wherein R2 and --COOCH3 are in the cis configuration). This reaction may be carried out at temperatures from about 0° C. to about 100° C., preferably about 25° C., for about 5 minutes to 18 hours. Treatment of the compound of formula XVI so formed with about 5 equivalents each of trimethyl aluminum and ammonium chloride in a nonpolar solvent such as benzene or toluene for about 0.5 to about 16 hours yields a compound of the formula XVII having the same stereochemistry. Reaction temperature may range from about room temperature to about 100° C., with about 50° C. being preferred.
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