A representative series of homopropargylic sulfonamides 19 and 22b have been found to undergo smooth 5-endo-dig cyclisation upon exposure to excess iodine in acetonitrile containing potassium carbonate. The resulting 4-iodo-2,3-dihydropyrroles 23 readily react with two equivalents of DBU in DMF at 20 °C to give the corresponding β-iodopyrroles 24 and 26 in excellent yields by the elimination of toluene-p-sulfinic acid. Use of less than two equivalents of base results in some loss of iodine. The iodo-2,3-dihydropyrroles 23 can be used in palladium-catalysed coupling reactions as shown by the efficient formation of the Sonogashira product 29 under
mild conditions.
研究发现,在含有
碳酸钾的
乙腈中接触过量
碘后,一系列具有代表性的均
丙炔基磺酰胺 19 和 22b 会发生顺利的 5-endo-dig 环化反应。生成的 4-
碘-2,3-二氢
吡咯 23 很容易与两当量的
DBU 在
DMF 中于 20°C 发生反应,通过消除
甲苯对
亚硫酸生成相应的 δ-
碘吡咯 24 和 26,收率极高。使用少于两个当量的碱会导致一些
碘损失。
碘-2,3-二氢
吡咯 23 可用于
钯催化的偶联反应,在温和的条件下有效地生成 Sonogashira 产物 29 即是证明。