sodium hydrogencarbonate in dichloromethane; water 3 h;

pyridinium p-toluenesulfonate in benzene 8 h; Reflux;

toluene-4-sulfonic acid in toluene 72 h; RefluxInert atmosphere;

in toluene

1: N,N,N',N,-tetramethylethylenediamine; sec.-butyllithium / diethyl ether / 2 h / -70 - -60 °C / |Inert atmosphere 2: potassium tert-butylate / isopropyl alcohol / 4 h / |Reflux; |Inert atmosphere 3: sodium methylate; 5 palladium on charcoal; hydrogen / methanol / 2 h / 50 °C / |Inert atmosphere View Scheme

1: 1,1-dimethylethyl 1,4-dioxo-8-azaspiro[4.5]-8-carboxylate With N,N,N',N,-tetramethylethylenediamine; sec.-butyllithium in diethyl ether T=-78 - -70°C; 5.5 h; 2: methyl iodide in diethyl ether T=-78 - 20°C;

1: 1,1-dimethylethyl 1,4-dioxo-8-azaspiro[4.5]-8-carboxylate With N,N,N',N,-tetramethylethylenediamine; sec.-butyllithium in tetrahydrofuran T=-78°C; 2 h; 2: methyl iodide in tetrahydrofuran T=-78 - 20°C; 16 h;