Bicyclo[2.2.1]heptane-1-methanesulfonic acid, 7,7-dimethyl-2-oxo-, (1S)- → (S)-tert-butyl 1-hydroxy-4-(1-methoxycyclopentyl)butan-2-ylcarbamate

The above (S)-tert-butyl 4-(2-(1-methoxycyclopentyl)ethyl)-2,2-dimethyloxazolidine-3-carboxylate (1170 mg, 3.5 mmol, 1.0 equiv) was dissolved in 40 mL of methanol. Camphorsulphonic acid (417 mg, 1.8 mmol, 0.5 equiv) was added and the mixture stirred for 4 h at ambient temperature. The mixture was quenched by addition of ca. 1 mL of NEt3 and the reaction evaporated. The residue was taken up in EtOAc, washed with brine, then dried over MgSO4, filtered through a pad of silica gel, and evaporated. This afforded 1.03 g (3.5 mmol, 100% yield) of the desired (S)-tert-butyl 1-hydroxy-4-(1-methoxycyclopentyl)butan-2-ylcarbamate.