A solution of (9H-fluoren-9-yl)methyl 2,5-dioxopyrrolidin-1-yl carbonate (3.2 g, 9.5 mmol) in dioxane (30 ml) was added to a solution of 3-amino-oxetane-3-carboxylic acid (1.17 g, mmol) and potassium carbonate (2.76 g, 20.0 mmol) in water (30 ml). The light yellow opaque solution was stirred at room temperature for 75 minutes. During that time, a white solid precipitated. The mixture was diluted with water and extracted two times with diethyl ether. The white solid did not dissolve and was kept therefore in the aqueous layer, which was acidified to pH 2 by addition of 1N HCl and extracted three times with EtOAc. The combined EtOAc layers were washed with brine, dried with Na2SO4 and evaporated. The crude title compound was obtained as white solid and was used without further purification.
