To a solution of 2.8 g (7.8 mmol) (3R,5R)-3-(tert-butyl-dimethyl-silanyloxy)-5-hydroxy-piperidine-1-carboxylic acid benzyl ester in 70 ml dry THF were consecutively added 1.0 g (8.5 mmol) benzoic acid, 1.7 g (8.5 mmol) diethyl azodicarboxylate and 2.2 g (8.5 mmol) triphenylphosphine at 0° C. After 6 h the reaction mixture was diluted with tert-butyl methyl ether washed with a 2N aqueous solution of sodium carbonate. The aqueous layer was extracted with 3 portions of tert-butyl methyl ether. The combined organic extracts were washed with a 2N aqueous solution of sodium carbonate and brine and dried over sodium sulfate. Flash chromatography gave 2.8 g (78%) of the title compound as a yellow oil.
