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Example 52(b) Synthesis of 5-bromopyridine-2-sulfonyl chloride: 2-(benzylthio)-5-bromopyridine (3.0 g, 10.71 mmol) was dissolved in dichloromethane (500 mL) in a 1 L Schlenk flask, followed by addition of water (250 mL) and formic acid (250 mL). The resulting non-homogeneous mixture was cooled to 0°C and chlorine gas was bubbled into the mixture through a Pasteur pipette under vigorous stirring. The chlorine gas was continuously passed for three minutes or until the mixture took on a deep yellow color. Upon completion of the reaction, the organic phase was separated and diluted with dichloromethane (100 mL). The aqueous phase was extracted with dichloromethane (3 x 250 mL) and the combined organic phases were washed sequentially with 1 M sodium hydroxide solution (500 mL) and saturated brine (500 mL). The organic phase was dried over anhydrous sodium sulfate and concentrated to afford the target product 5-bromopyridine-2-sulfonyl chloride (2.73 g, 99% yield). Mass spectrum (ESI) m/z 258 ([M+H]+).

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