One-Pot Sulfonylated Pyridines

Process chemists at Merck & Co. report concise synthesis of functionalized sulfonylated pyridines—valuable building blocks in both medicinal and agricultural chemistry (Org. Lett., DOI: 10.1021/ol102629c). Besides their utility as intermediates in organic synthesis, these compounds have been shown to be anti-­inflammatory, antihyperglycemic, and ­immunosuppressive agents, as well as inhibitors of HIV-1 reverse transcriptase. Sulfonylated pyridines are typically synthesized by displacing a halogen from a halopyridine with a thiol in basic solution, followed by oxidation. But this two-step approach is problematic because of the odiferous thiols and the large amount of hazardous waste generated. Merck’s Kevin M. Maloney, Jeffrey T. Kuethe, and Kathleen Linn developed a more streamlined nucleophilic aromatic substitution reaction in which a sulfinic acid salt converts chloropyridines directly to sulfonylated pyridines. The one-pot reactions, accelerated by the addition of tetrabutylammonium chloride (TBACl) as a phase-transfer catalyst, provided high yields and required no chromatographic purification. The team prepared a variety of sulfonylated pyridines starting from chloropyridines, substituted chloropyridines, and dichloropyridines. “The method is safe, scalable, and significantly greener than current alternatives,” the researchers write.