An approach to 2,3-dihydropyrroles and β-iodopyrroles based on 5-endo-dig cyclisations
作者:David W. Knight、Adele L. Redfern、Jeremy Gilmore
DOI:10.1039/b110751h
日期:2002.2.22
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。