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 three hours at room temperature, and the aqueous phase is separated off and extracted twice with 100 ml of methylene chloride each time. The organic solutions are dried over magnesium sulphate and concentrated, and the residue is distilled.
