[CH3:1][N:2]1[C:6](=[O:7])[NH:5][NH:4][C:3]1=[O:8].C1C=CC=CC=1.CN(C)C=O.CC(C)([O-])C.[K+].[CH:26]([C:28]([CH2:30][CH2:31][CH2:32][CH2:33][CH3:34])=[O:29])=[CH2:27]>CN(C)C=O>[O:29]=[C:28]([CH2:30][CH2:31][CH2:32][CH2:33][CH3:34])[CH2:26][CH2:27][N:4]1[C:3](=[O:8])[N:2]([CH3:1])[C:6](=[O:7])[NH:5]1
A solution of 4-methyl-1,2,4-triazolidine-3,5-dione (16 g; 0.14 mmole) in dry 1:1 benzene-dimethylformamide (100 ml) was heated under reflux, with stirring under nitrogen, and potassium t-butoxide (17.62 g), was added. The resultant suspension was heated under reflux for 2 hr. and then n-pentyl vinyl ketone (12,568; 0.10 mole) in dry dimethylformamide (10 ml) added dropwise. After 2 days the mixture was allowed to cool to room temperature and partitioned between 5 M HCl (200 ml) and ethyl acetate (100 ml). The aqueous layer was extracted with ethyl acetate (5×70 ml) and the combined organic layers washed with water (2×100 ml) and brine (100 ml) and dried (Na2SO4). Evaporation in vacuo gave an oil. Recrystallisation from ethyl acetate - 60/80 petroleum ether gave 2-(3'-oxo-octyl)-4-methyl-1,2,4-triazolidine-3,5-dione (16.03 g; 66%). m.pt., 75°-76°
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