0.7 ml of Jones' reagent (chromium trioxide/4N aqueous sulfuric acid: Bowden, Heibron, Jones & Weedon, J. Chem. Soc., 1946, 39) was added, whilst ice-cooling, to a solution of 245 mg (0.74 mmol) of (3R)-1-t-butoxycarbonyl-3-t-butyldimethylsilyloxy-L-prolinol [prepared as described in step (a) above] in 10 ml of acetone, and the mixture was stirred at 0° C. for 2 hours. At the end of this time, the reaction mixture was diluted with water and extracted with diethyl ether. The extract was washed with a saturated aqueous solution of sodium chloride and dried over anhydrous sodium sulfate. The solvent was then removed by distillation under reduced pressure, and the residue was triturated with hexane, to give 191 mg of the title compound as colorless crystals, melting at 146°-147° C.
