[CH2:1]([C:3]1[N:7]=[C:6]([CH:8]([CH3:12])[C:9]([OH:11])=O)[O:5][N:4]=1)[CH3:2].[CH2:13]([N:16]=C=O)[CH2:14][CH3:15].COC1C=C[N+]([O-])=CC=1.O>C1(C)C=CC=CC=1.C(N1C=CN=C1)=C>[CH2:13]([NH:16][C:9](=[O:11])[CH:8]([C:6]1[O:5][N:4]=[C:3]([CH2:1][CH3:2])[N:7]=1)[CH3:12])[CH2:14][CH3:15]
Employing anhydrous conditions, 17 mmol of about 90% pure α-(3-ethyl-1,2,4-oxadiazol-5-yl)-propionic acid (=3 ethyl-α-methyl-1,2,4-oxadiazol-5-yl-acetic acid) were dissolved in 40 ml of toluene and about 20.5 mmol of n-propyl-isocyanate and about 60 mg of the catalyst (a saturated solution of 4-methoxy-pyridine-1-oxide.1 H2O in N-vinyl-imidazole) were added to the solution. While a slow stream of nitrogen was continuously passed over the surface, the reaction mixture was stirred for 5.5 hours at room temperature and the reaction mixture was evaporated in vacuo. The residue was dissolved in 100 ml of a 1:1 mixture of ethyl acetate and diethyl ether and this solution was extracted 4 times at pH 2.0 with 10 ml of water. The combined acid washings were extracted once with 10 ml of ethyl acetate and discarded. The two organic layers were combined and extracted 3 times at pH 7.0 with 10 ml of water. The combined washings were extracted once with 10 ml of ethyl acetate and discarded. The combined organic layers were treated with activated carbon, dried over anhydrous magnesium sulfate, filtered and completely evaporated in vacuo. The residue was stirred in 20 ml of n-hexane, whereupon diethyl ether was added slowly till the solid was almost completely dissolved. After filtration, the solution was gradually cooled to -18° C. and the crystalline precipitate was collected by filtration, washed repeatedly with n-hexane and with very cold diethyl ether to obtain 1.7 g (about 50% yield) of N-propyl-α-(3-ethyl-1,2,4-oxadiazol-5-yl)-propionamide with a purity of about 95% (according to TLC and PMR spectrum) and a m.p. of 52°-53° C.
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