Methanol → Methyl 5-(2,4-dichlorophenyl)-4-imidazol-2-yl-5-oxo-2-phenylthiopentanoate

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A solution (1 M) of tert-butoxide in tert-butanol (54.9 ml) was added to a stirred solution of 1-(2,4-dichlorophenyl)-2-imidazol-2-ylethan-1-one (0.11 M) and methyl 2-phenylthioprop-2-enoate (0.14 M) dissolved in dichloromethane (300 ml) and methanol (200 ml) at room temperature. The reaction, which developed a dark color, was typically stirred overnight (ca. 16 h) under argon. The reaction was monitored by TLC using 5% methanol in dichloromethane as the solvent system. Additional methyl 2-phenylthioprop-2-enoate was added as needed to consume all of the starting 1-(2,4-dichlorophenyl)-2-imidazol-2-ylethan-1-one. The reaction was quenched by the addition of sat. aq. NH4Cl (˜100 ml). The mixture was transferred to a separatory funnel and diluted with ethyl acetate (300 ml). The aqueous layer was removed and the organic layer was washed with sat. aq. NH4Cl (3×100 ml), brine (100 ml), and dried with Na2SO4. After filtration and evaporation, the residue was purified by flash chromatography over silica gel. The column was eluted starting with 100% dichloromethane to remove the non-polar methyl 2-phenylthioprop-2-enoate. The product was eluted with 3% methanol in dichloromethane. After drying overnight in vacuo, methyl 5-(2,4-dichlorophenyl)-4-imidazol-2-yl-5-oxo-2-phenylthiopentanoate as a deep red glass was obtained in 71% yield. A further 10% yield of product could be obtained by resubmitting side product contaminated fractions to a second purification by flash chromatography.

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