13 g (61.2 mmol) of tert.-butyl 2,7-diazabicyclo[3.3.0]octane-7-carboxylate are dissolved in 100 ml of toluene, a solution of 3 g of sodium hydroxide in 20 ml of water is added, and 7 g (64.5 mmol) of ethyl chloroformate are added dropwise at room temperature. The mixture is stirred for 3 hours at room temperature, and the aqueous phase is separated off and extracted twice using 100 ml portions of methylene chloride. The organic solutions are dried over magnesium sulphate, concentrated and distilled.
