[CH:1]([CH:3]=[CH2:4])=O.[NH2:5][C:6]([CH2:13][CH2:14][CH3:15])=[CH:7][C:8]([O:10][CH2:11][CH3:12])=[O:9].[S].C(OCC)C>N1CCCCC1.C(O)C.O>[CH2:13]([C:6]1[C:7]([C:8]([O:10][CH2:11][CH3:12])=[O:9])=[CH:4][CH:3]=[CH:1][N:5]=1)[CH2:14][CH3:15]Acrolein (30 g, 0.52 mmol) was added during a period of 2 hours to a stirred solution of ethyl 3-amino-hex-2-enoate (62 g, 0.4 mmol) dissolved in 2 g of piperidine and 300 ml of anhydrous ethanol. The mixture was refluxed for 3 hours and the ethanol was evaporated. The remaining oil was heated to 100° C. and solid sulfur (52 g, 1.6 mmol) was carefully added in portions. The temperature was elevated to 150° C. for 3 hours. The mixture was cooled to room temperature and 200 ml of diethyl ether and 800 ml of water was added. The organic material was extracted into diethyl ether (2×200 ml). The combined organic layer were dried overmagnesium sulfate, and evaporated to an oil. The crude product was purified by column chromatography over silica gel 60, using diethyl ether as the eluent to afford 50 g (65%) of ethyl 2-n-propylpyridine-3-carboxylate as an oil. 1H--NMR (CDCl3, 200 MHz) δ: 1.01 (t, 3 H); 1.40 (t, 3 H); 1.75 (sextet, 2 H); 3.12 (t, 2 H); 4.38 (q, 2 H); 7.19 (dd, 1 H); 8.13 (dd, 1 H); 8.63 (dd, 1 H).
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