To a mixture of tert-butyl 10-(methoxymethyl)-11-oxa-3,8-diazaspiro[5.5]undecane-3-carboxylate and K2CO3 (115 mg, 0.832 mmol) in acetonitrile (1.4 mL) was added 1-bromopropan-2-one (304 mg, 2.00 mmol). The reaction mixture was heated under argon in a sealed tube for 16 h. The mixture was cooled, diluted with dichloromethane and washed with water. The organic layer was dried over Na2SO4, filtered and concentrated in vacuo to provide tert-butyl 2-(methoxymethyl)-4-(2-oxopropyl)-1-oxa-4,9-diazaspiro[5.5]undecane-9-carboxylate. ESI-MS m/z calc. 356.2. Found 357.3 (M+1)+; Retention time: 0.98 minutes (3 min run).
