6.1 g (25 mmol) of t-butyl 2-(2-amino-4-thiazolyl)-2-(Z)-hydroxyimino-acetate are dispersed in 250 ml of dry acetonitrile. 13.7 g (50 mmol) of p-nitrobenzyl bromoacetate and 12.9 ml (75 mmol) of N-ethyldiisopropylamine are now added thereto at room temperature while stirring. 7.5 g (50 mmol) of sodium iodide are added thereto 5 minutes later. The mixture is stirred at room temperature for 3.5 hours in an argon atmosphere. The solvent is subsequently removed by evaporation and the residue is diluted with 500 ml of ethyl acetate. The solution obtained is washed four times with a total of 2 l of water. The aqueous phase is extracted with 300 ml of ethyl acetate and the combined ethyl acetate solutions are dried over sodium sulphate and evaporated to dryness. After crystallization from ethyl acetate/hexane, there are obtained 8.2 g (75%) of t-butyl 2-(2-amino-4-thiazolyl)-2-[[(p-nitrobenzyloxycarbonyl)methoxy]imino]-acetate of melting point 146.8° C. (decomposition).
