[CH3:1][C:2]1[C:6]([OH:7])=[C:5]([C:8]([O:10][CH:11]([CH3:13])[CH3:12])=[O:9])[S:4][C:3]=1[C:14]([O:16][CH:17]([CH3:19])[CH3:18])=[O:15].C(N(CC)CC)C.[C:27](Cl)(=[O:34])[C:28]1[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=1>O1CCOCC1>[CH3:1][C:2]1[C:6]([O:7][C:27](=[O:34])[C:28]2[CH:33]=[CH:32][CH:31]=[CH:30][CH:29]=2)=[C:5]([C:8]([O:10][CH:11]([CH3:13])[CH3:12])=[O:9])[S:4][C:3]=1[C:14]([O:16][CH:17]([CH3:19])[CH3:18])=[O:15]A mixture of di-isopropyl 3-methyl-4-hydroxy-2,5-thiophene-dicarboxylate (656 g, 2.30 mol), triethylamine (297 g, 2.98 mol) and dioxane (2 l) was cooled with ice to about 10° C. The solution was added, while stirring, with benzoyl chloride (351 g, 2.5 mol) over about 10 minutes, followed by further stirring for 30 minutes at room temperature. After removing the precipitate of triethylamine hydrochloride salt by filtration, the solution was distilled in vacuo to remove dioxane. Toluene was then added to the remaining residue, and the solution was washed with 5% aqueous sodium bicarbonate and water, and then dried over MgSO4. The solvent was removed by distillation to give almost pure di-isopropyl 3-methyl-4-benzoyloxy-2,5-thiophene dicarboxylate (851 g, 95%). nD10 1.5499.
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