Benzaldehyde → 1-((3R)-6,8-Difluoro-3,4-dihydro-2H-1-benzopyran-3-yl)-1,3-dihydro-5-(2-((phenylmethyl)amino)ethyl)-2H-imidazole-2-thione

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Reaction Steps

To (R)-5-(2-aminoethyl)-1-(6,8-difluorochroman-3-yl)-1,3-dihydroimidazole-2-thione (2.36 g, 7.58 mmol) and benzaldehyde (0.85 ml, 8.34 mmol) in a mixture of methanol (15 ml), and dichloromethane (15 ml) sodium cyanoborohydride (0.67 g, 10.66 mmol) was added at 20-25° C. in portions. The mixture was stirred for 64 h, quenched with 1N HCl (12 ml) with stirring followed by 3N NaOH (12 ml). The mixture was extracted with DCM (100 ml), the organic phase was washed with brine (50 ml), dried (MgSO4) and evaporated to dryness. The residue was purified on a silica gel column with ethyl acetate and a mixture of ethyl acetate with methanol (9:1) as eluents. Fractions containing the product were collected, evaporated under reduced pressure to approx 20 ml then cooled on ice. The precipitate was collected, washed with ethyl acetate—petroleum ether (1:1) mixture, dried on air. Yield was 1.25 g (41%), the product having a mp 188-90° C. (2-propanol-DCM).

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