[CH3:1][N:2]1[C:6](=[O:7])[NH:5][NH:4][C:3]1=[O:8].[H-].[Na+].[CH2:11]=[CH:12][C:13](=[O:19])[CH2:14][CH2:15][CH2:16][CH2:17][CH3:18]>CN(C)C=O.C(OCC)(=O)C>[CH3:1][N:2]1[C:6](=[O:7])[NH:5][N:4]([CH2:11][CH2:12][C:13](=[O:19])[CH2:14][CH2:15][CH2:16][CH2:17][CH3:18])[C:3]1=[O:8]To a solution of 4-methyl-1,2,4-triazolidine-3,5-dione (5.75 g, 0.05 mol) in dry dimethylformamide (40 ml) stirred at 75° under a nitrogen atmosphere was added portionwise sodium hydride (1.575 g, 0.055 mol, as an 80% dispersion in mineral oil) and the resultant solution stirred at 75° for 0.5 hr. To this solution was added oct-1-en-3-one (6.57 g, 0.055 mol) dropwise in dimethylformamide (20 ml) and the solution heated with stirring for 48 hr at 75°. The reaction mixture was then cooled, taken up in ethyl acetate (100 ml) and poured into ice-cold 5N aqueous hydrochloric acid (200 ml). The aqueous layer was separated and extracted with ethyl acetate (4×100 ml). The combined extracts were washed with 5N aqueous hydrochloric acid, water and then brine, then dried (Na2SO4), filtered and the solvent removed by evaporation in vacuo, to leave a gum (6.55 g). This was chromatographed on silica gel (Merck, Kieselgel 60) with a packing ratio of 1:20 with chloroform as eluant, to afford the triazolidine-3,5-dione (4.61 g) as a gum, which later solidified. (In subsequent preparations the crude material from the reaction mixture could be triturated with hexane to induced crystallisation), m.p. 76°-8°.
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