[CH3:1][O:2][C:3](=[O:10])[CH2:4][C:5]1[S:6][CH:7]=[CH:8][CH:9]=1.Cl.[CH2:12]=O.[CH3:14][S:15]([NH2:18])(=[O:17])=[O:16]>O1CCOCC1.[Cl-].[Zn+2].[Cl-].CCOC(C)=O>[CH3:1][O:2][C:3](=[O:10])[CH2:4][C:5]1[S:6][C:7]([CH2:12][NH:18][S:15]([CH3:14])(=[O:17])=[O:16])=[CH:8][CH:9]=1
To a solution of thiophen-2-yl-acetic acid methyl ester (2 mL, 12.8 mmol) in 1,4-dioxane (10 mL) was added concentrated HCl (0.4 mL, 4.8 mmol) dropwise over 10 minutes. Zinc chloride (78 mg, 0.57 mmol) was added and the reaction was lowered into a pre-heated water bath at 45° C. and was stirred for 15 minutes. HCl (g) was bubbled into the solution for 2-3 minutes. The temperature of the reaction rose to about 60° C. Upon cooling, 37% aqueous formaldehyde (1.24 mL, 16 mmol) was added dropwise and the temperature rose to 70° C. The reaction was cooled to room temperature and methanesulfonamide (1.25 g, 12.8 mmol) was added in portions. The reaction was stirred for 3 h and was poured into EtOAc (60 mL). The organic solution was washed with water and the aqueous solution was washed with EtOAc (60 mL). The combined organic solutions were washed with brine, dried over MgSO4, filtered, and concentrated. Purification by flash chromatography (CHCl3) provided the title compound (69%) as a gold oil. 1H NMR (400 MHz, CDCl3) δ 6.85 (d, 1H), 6.70 (d, 1H), 5.20 (m, 1H), 4.40 (s, 2H), 3.80 (s, 2H), 3.70 (s, 3H), 2.80 (s, 3H).
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