[C:1]([C:4]1[CH:9]=[CH:8][C:7]([N:10]2[C:14](=[O:15])[NH:13][NH:12][C:11]2=[O:16])=[CH:6][CH:5]=1)(=O)[CH3:2].Cl.[CH2:18]([O:21][NH2:22])[C:19]#[CH:20].Cl.O1CCOCC1>C(O)C>[CH2:18]([O:21]/[N:22]=[C:1](/[C:4]1[CH:9]=[CH:8][C:7]([N:10]2[C:14](=[O:15])[NH:13][NH:12][C:11]2=[O:16])=[CH:6][CH:5]=1)\[CH3:2])[C:19]#[CH:20]
To 4-(4-acetylphenyl)-1,2,4-triazolidine-3,5-dione (500 mg, 2.281 mmol) in ethanol (6.912 mL) was added O-(prop-2-ynyl)hydroxylamine hydrochloride (368 mg, 3.42 mmol) and HCl 4N in dioxane (1.711 mL, 6.84 mmol). The mixture was stirred at 50° C. for 2 hours and then concentrated in vacuo. Saturated sodium bicarbonate was added, extracted with ethyl acetate twice, dried over MgSO4, filtered, and concentrated in vacuo. The residue was purified by silica gel chromatography (60-100% ethyl acetate/heptane, and then 5% MeOH/ethyl acetate) giving (E)-4-(4-(1-(prop-2-ynyloxyimino)ethyl)phenyl)-1,2,4-triazolidine-3,5-dione (I-6a: 46 mg, 7%) as a white solid. LC-MS (M+1) 273.1, t=0.81 minute. 1H NMR (400 MHz, DMSO-d6) δ ppm 2.23 (s, 3 H) 3.48 (t, J=2.40 Hz, 1 H) 4.80 (d, J=2.27 Hz, 2 H) 7.53 (d, J=8.59 Hz, 2 H) 7.76 (d, J=8.59 Hz, 2 H) 10.52 (s, 2 H).
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