A mixture of methyl thiosalicylate (2.80 g, 16.6 mmol), a mixture of tert-butyl 3-[(2-cyanopyridin-3-yl)propoxy]propionate and tert-butyl 3-[(2-cyanopyridin-5-yl)propoxy]propionate (ca. 9:1, 4.55 g, 15.7 mmol), triethylamine (2.02 g, 20 mmol) and toluene (20 ml) was refluxed under nitrogen atmosphere for 20 hrs. The reaction mixture was concentrated under reduced pressure. The residue was subjected to a silica gel column chromatography, eluted with ethyl acetate-hexane (2:1, v/v) to give the titled compound (1.10 g, 16%).
