Oxalyl chloride (3.5 ml, 40 mmol) was added to a solution of (3aS,4S,6R,6aR)-6-methoxy-2,2-dimethyltetrahydrofuro[3,4-d][1,3]dioxole-4-carboxylic acid (Justus Liebigs Ann. Chem., 1974, 11, 1856) (3 g, 13.8 mmol) in dichloromethane (25 ml). The solution was stirred at room temperature for 3 hours and the solvent was then evaporated under reduced pressure. The acid chloride was re-dissolved in dichloromethane (25 ml) and treated with benzyl carbazate (2.3 g, 13.8 mmol) and triethylamine (5.7 ml, 41.4 mmol). After having been stirring at room temperature for 12 hours, the mixture was partioned between ethyl acetate (100 ml) and water (50 ml). The ethyl acetate layer was separated, washed with 1M aqueous citric acid solution (50 ml), saturated sodium hydrogencarbonate solution (50 ml) and brine (50 ml) and dried (anhydrous sodium sulphate). Evaporation of solvent under reduced pressure yielded the title compound as a yellow foam (4.87 g).
