[N:1]1[CH:6]=[CH:5][C:4]([CH3:7])=[CH:3][CH:2]=1.[Br:8][CH2:9][CH2:10][S:11][S:12][CH2:13][CH2:14]Br.[CH3:16][N:17]1[CH2:21][CH2:20][CH2:19][C:18]1=O.[C:23](#N)C>>[Br-:8].[Br-:8].[S:12]([CH2:13][CH2:14][N+:17]1[CH:16]=[CH:23][C:19]([CH3:18])=[CH:20][CH:21]=1)[S:11][CH2:10][CH2:9][N+:1]1[CH:6]=[CH:5][C:4]([CH3:7])=[CH:3][CH:2]=167 g of 4-picoline are diluted in 100 ml of acetonitrile and the mixture is heated to 80° C. A mixture of 60 g of 1-bromo-2-[(2-bromoethyl)disulphanyl]ethane and 15 ml of N-methylpyrrolidone (NMP) is added over 5 minutes. After 4 hours of stirring at 85° C., the mixture is cooled. The solid obtained is filtered off, rinsed with 3×200 ml of acetonitrile and then dissolved in 800 ml of isopropanol (at reflux). After cooling, 1 l of ethyl ether is added. The precipitate formed is filtered off, rinsed with 3×200 ml of ethyl ether and then dried. The off-white powder obtained (73.77 g) contains a great majority (>90%) of the expected product, which is used as it is for the following step.
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