Triethylamine (15 mmol) is added to an ice-cold stirring suspension of p-carboxybenzene sulfonylazide (5 mmol) and 3-azido-4-(3-benzyloxycarbonyl-2-oxopropyl)-azetidin-2-one (5 mmol) in anhydrous acetonitrile (30 ml). The resulting mixture is stirred at room temperature for 90 mins, then diluted with ethylacetate and filtered. The filtrate is washed with water, 0.5 N sodium hydroxide, water, and brine, dried over magnesium sulfate, filtered, and evaporated under vacuum to give 3-azido-4-(3-benzyloxycarbonyl-3-diazo-2-oxopropyl)-azetidin-2-one.
