A yellow solution of 4-{[(2,4-dimethoxy-benzyl)-ethoxycarbonylmethyl-amino]-methyl}-2-phenyl-thiazole-5-carboxylic acid ethyl ester (5.60 g, 0.01 mol) in THF (45 mL) was added 1 M potassium tert-butoxide (KOtBu) in THF (24.7 mL, 0.02 mmol) at −78° C., a dark red suspension quickly appeared. The mixture was stirred at −78° C. for 20 min, warmed to room temperature and stirred at that temperature for 2 h before it was quenched with aqueous ammonium chloride, extracted with ethyl acetate. The organic layer was washed with water, brine, dried over anhydrous sodium sulfate and concentrated in vacuo to give 5-(2,4-dimethoxy-benzyl)-7-oxo-2-phenyl-4,5,6,7-tetrahydro-thiazolo[4,5-c]pyridine-6-carboxylic acid ethyl ester as a yellow oil (4.63 g). It was dissolved in dichloromethane (40 mL) and thionyl chloride (1.12 mL, 0.02 mmol) was added drop wise. The mixture was stirred at room temperature for 3.5 h before it was quenched with saturated sodium bicarbonate, extracted with dichloromethane. The organic layer was washed with water, brine, dried over anhydrous sodium sulfate and concentrated in vacuo. The residue was purified by flash column chromatography on silica gel with a gradient of ethyl acetate and dichloromethane to give the title compound as a yellow solid (2.74 g): 1H NMR (CDCl3, 200 MHz): δ=11.52 (s, 1H), 9.00 (s, 1H), 8.13 (m, 2H), 7.55 (m, 3H), 4.58 (q, J=7.0 Hz, 2H), 1.53 (t, J=7.0 Hz, 3H); MS: (+) m/z 301.0 (M+1).
