Tetramethylene sulfoxide → 2-Chloro-5-[(1-oxidotetrahydrothien-2-yl)methyl]-pyridine

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Tetramethylene sulfoxide (6.5 g, 62 mmol) was dissolved in 30 mL anhydrous THF, stirred and cooled to −70° C. and then treated with 2.5 M n-BuLi in hexane (24 mL, 61 mmol) over a period of 10 min. The temperature was raised to −20 to −30° C. (Liquid N2/o-xylene bath) and the mixture was stirred for a further 30 min. The mixture was cooled to −70° C. and treated dropwise with a solution of 6-chloro-3-chloromethylpyridine in 15 mL THF. The reaction was stirred for 2 h at −70° C. and then treated dropwise with trifluoroacetic acid (8.0 g, 70 mmol). The mixture was warmed to room temperature, poured into 75 mL water and extracted with dichloromethane (2×50 mL). The combined organic extracts were washed with dilute sodium bicarbonate and saturated NaCl, dried over Na2SO4 and concentrated. The residue was chromatographed on silica gel with 5% methanol in dichloromethane to give 2.5 g of the desired sulfoxide as a brown oil in 35% yield.

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