Diethyl Oxalate → (3,4,5-Tribromothiophen-2-yl)-oxo-acetic acid ethyl ester

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To tetrabromothiophene (2.0 g, 5.0 mmol) in an oven dried 50 mL flask, evacuated and flushed with nitrogen, was added anhydrous diethyl ether (12 ml). The resulting solution was cooled to −18° C., then n-butyllithium (1.6 M in hexane) (3.1 ml, 5.0 mmol ) was added dropwise via a syringe. After stirring for 10 min at −18° C., diethyl oxalate (0.75 ml, 5.5 mmol) was added dropwise. Stirring was continued for 30 min, then the reaction mixture was quenched with 1N HCl. The organic layer was separated, dried over Na2SO4 and concentrated under vacuum. Purification was performed by column chromatography using hexane/ethyl acetate (20:1) to yield (3,4,5-tribromothiophen-2-yl)-oxo-acetic acid ethyl ester as a yellow solid (1.5 g, 71%). MS (M+H)+: 422.55; 1H NMR (300 MHz, CDCl3) δ4.45 (2H, q, J=7.1 Hz), 1.44 (3H, t, J=7.1 Hz). 13C NMR (75 MHz, CDCl3) δ173.89, 161.64, 133.35, 124.81, 123.05, 122.54, 63.75, 14.11.

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