To a stirring 0° C. solution of triphenylphosphine (1.2 equiv) in 23 mL of THF was added di-tert-butyl azodicarboxylate (1.2 equiv). The mixture was stirred at 0° C. for 10 minutes. Then a solution of (3R,5R)-benzyl 3-(tert-butyldimethylsilyloxy)-5-hydroxypiperidine-1-carboxylate (1.0 equiv) in 11 mL of THF was added and stirred for 20 minutes at 0° C. Benzoic acid (1.2 equiv) was then added and the reaction mixture was allowed to slowly warm to rt. After 16 hours the reaction mixture was concentrated in vacuo then diluted with EtOAc and washed with water then brine. The organic layer was dried with Na2SO4, filtered, and concentrated in vacuo. The crude residue was purified by flash chromatography (EtOAc:hexanes=1:8) to yield (3S,5R)-benzyl 3-(benzoyloxy)-5-(tert-butyl-dimethylsilyloxy)piperidine-1-carboxylate (77%). LC/MS (m/z): 470.2 (MH+), HPLC Rt=6.05 min.
