Sodium borohydride → Benzyl carbamate

To a solution of (9-oxo-3-thia-bicyclo[3.3.1]non-7-yl)-carbamic acid benzyl ester (16, 4.2 g, 13.7 mmol) in ethanol (172 ml) was added sodium borohydride (0.78 g, 20.6 mmol) portionwise at room temperature. The solution was stirred for 1 hour before addition of sodium borohydride (0.2 g, 5 mmol). The reaction mixture was stirred for 2 days, a further portion of sodium borohydride (0.340 g, 9 mmol) was added, and stirring was continued for 4 hours. The mixture was then concentrated under reduced pressure and cold water was added to the residue as well as dichloromethane. After a extraction of the aqueous phase with dichlormethane, the combined organic layer was dried over anhydrous sodium sulphate, filtered and concentrated under reduced pressure. The crude product was purified by silica gel chromatography (cyclohexane:ethyl acetate 40:60) to yield 9-hydroxy-3-thia-bicyclo[3.3.1]non-7-yl)-carbamic acid benzyl ester as a white solid (0.84 g).