2-Chloromethylbenzimidazole → (E)-2-(4-[2-Phenylethenyl]-1,2,3,6-tetrahydropyridin-1-ylmethyl)benzimidazole

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A solution of 4-styrylpyridine (4.0 g, 22.1 mmol) and 2-chloromethylbenzimidazole (3.7 g, 22.1 mmol) in dimethylformamide (20 ml) was heated at 110°-120° C. under a nitrogen atmosphere for 1.5 hours. The mixture was cooled to room temperature, diluted with ethanol (380 ml) and carefully treated with sodium borohydride (880 mg, 23.2 mmol). The mixture was stirred at room temperature for 2 hours, then heated at reflux for 1 hour before stirring at room temperature overnight. The ethanol was evaporated in vacuo and the residue partitioned between ethyl acetate (100 ml) and sodium carbonate (half saturated, 100 ml). The phases were separated and the aqueous was extracted with ethyl acetate (2×100 ml). The combined organics were washed with water (50 ml) and brine (50 ml), dried (MgSO4) and evaporated in vacuo to give a reddish gummy residue which was purified by flash chromatography (eluting with 5% methanol in dichloromethane) to give a yellow gummy solid. The gum was triturated with ethyl acetate and recrystallised from ethyl acetate to give the title compound as a mustard solid (912 mg, 13%). M.p. 225°-227° C. (EtOAc); (Found: C, 79.74; H, 6.89; N, 13.47. C21H21N3 requires C, 79.97; H, 6.71; N, 13.32%); δH (DMSO-d6) 2.37 (2H, br s, tetrahydropyridinyl CH2), 2.69 (2H, t, J 5.6 Hz, tetrahydropyridinyl CH2), 3.17 (2H, br s, tetrahydropyridinyl CH2), 3.83 (2H, s, NCH2Ar), 5.91 (1H, s, CH=CR), 6.48 (1H, d, J 16.2 Hz, CHCHPh), 6.91 (1H, d, J-16.2 Hz, CHPh), 7.13-7.22 (3H, m, ArH), 7.29-7.33 (2H, m, ArH), 7.42-7.47 (3H, m, ArH), 7.54 (1H, m, ArH), and 12.31 (1H, br s, NH); m/z (CI+, NHs) 316 (M+1)+.

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