4-Ethoxycarbonyl-5-iodothiazole (71.47 g) was dissolved in 250 ml of DMF. Triethylamine (70 ml), 53.4 ml of ethynyltrimethylsilane, 960 mg of copper(I) iodide, and 3.54 g of bis(triphenylphosphine) palladium(II) dichloride were added in that order, and the mixture was stirred at 60° C. under an argon atmosphere for 1.5 hr. The reaction solution was added to 1000 ml of ethyl acetate and 500 ml of brine. The mixture was adjusted to pH 3 by the addition of 1 N aqueous hydrochloric acid. The organic layer was separated and was washed with 500 ml of sodium bicarbonate water and 500 ml of brine in that order. The organic layer was dried over anhydrous magnesium sulfate, was filtered, and was concentrated under the reduced pressure. The residue was purified by column chromatography on silica gel (hexane:ethyl acetate=4:1 to 3:1) to give 53.66 g of 5-(2-trimethylsilylethynyl)-4-ethoxycarbonylthiazole. This product was dissolved in 250 ml of methanol, 3.1 of potassium carbonate was added to the solution under ice cooling, and the mixture was stirred at the same temperature for 45 min. The reaction solution was added to 500 ml of ethyl acetate and 250 ml of brine. The organic layer was separated and was washed twice with 500 ml of brine. The organic layer was dried over anhydrous magnesium sulfate, was filtered, and was concentrated under the reduced pressure. The residue was purified by column chromatography on silica gel (hexane:ethyl acetate=2:1 to 1:1) to give 29.91 g of 5-ethynyl-4-methoxycarbonylthiazole.
