Sodium hydride → (R)-tert-butyl 4-(2-methoxy-2-oxoethyl)-5-oxo-3-phenyl-8,11-dioxa-1,4-diazaspiro[5.6]dodecane-1-carboxylate

24 mg (0.55 mmol) sodium hydride were added to 0.18 g (0.5 mmol) (3R)-tert-butyl 5-oxo-3-phenyl-8,11-dioxa-1,4-diazaspiro[5.6]dodecane-1-carboxylate in 3 ml DMF. After 5 min at RT 54 μl (0.91 mmol) methyl bromoacetate were added and then the reaction mixture was stirred for 1 h at RT. The reaction was poured onto ice water and extracted with ethyl acetate. The organic phase was washed with water, dried and evaporated down.