Part 7. dimethyl (2S,3S,5R)-5-hydroxy-2-[(4-phenylpiperazin-1-yl)carbonyl]piperidine-1,3-dicarboxylate: To a mixture of (2S,3S,5R)-5-hydroxy-3-(methoxycarbonyl)piperidine-2-carboxylic acid (3.140 g, 0.01545 mol), 1-phenyl-piperazine (2.597 mL, 0.01700 mol) and benzotriazol-1-yloxytris(dimethylamino)phosphonium hexafluorophosphate (7.518 g, 0.01700 mol) in N,N-dimethylformamide (10.00 mL, 0.1291 mol) was added N,N-diisopropylethylamine (3.230 mL, 0.01854 mol) at 0 Celsius. After stirred at rt overnight the reaction mixture was diluted with methylene chloride (90.0 mL, 1.40 mol) and then cooled to 0 Celsius. To the mixture was added N,N-diisopropylethylamine (5.38 mL, 0.0309 mol) followed by methyl chloroformate (2.39 mL, 0.0309 mol). The mixture was stirred at rt for 2 h and then concentrated to dry. The residue was diluted with water and extracted with ethyl acetate. The combined organic layers were washed with brine, dried and concentrated to dry. The residue was purified on silica gel, eluting with 0 to 100% EtOAc in hexane, to give the titled compound (5.20 g, 83.0%). MS (ESI): (M+H)+=406.1.
