Nitropyridines: X. Palladium-catalyzed cross-coupling of 2-bromo-5-nitropyridine with terminal acetylenes

Substituted 5-nitro-2-ethynylpyridines were synthesized by the Sonogashira reaction of 2-bromo-5-5-nitropyridine with terminal acetylenes. Desilylation, oxidative decarbonylation, and the retro-Favorskii reaction of the cross-coupling products of 2-bromo-5-nitropyridine with trimethylsilylacetylene, prop-2-ynyl alcohol, and 2-methylbut-3-yn-2-ol, respectively, gave 2-ethynyl-5-nitropyridine. The hydration of 2-ethynyl-5-nitropyridine and 5-nitro-2-(phenylethynyl)pyridine according to Kucherov afforded 2-acetyl-5-nitropyridine and 5-nitro-2-phenacylpyridine, respectively.