Dipartimento di Chimica e Tecnologie Chimiche, Università della Calabria, Ponte Pietro Bucci 12/C, Arcavacata di Rende (CS) 87036, Italy.
Molecules. 2013 Sep 4;18(9):10901-11. doi: 10.3390/molecules180910901.
A recyclable palladium-catalyzed synthesis of 2-methylene-2,3-dihydrobenzofuran-3-ols 2 by heterocyclization of 2-(1-hydroxyprop-2-ynyl)phenols 1 in an ionic liquid medium (BmimBF4) is presented. The process takes place under relatively mild conditions (100 °C, 5 h) in the presence of catalytic amounts (2 mol %) of PdI2 in conjunction with KI (5 equiv with respect to PdI2) and an organic base, such as morpholine (1 equiv with respect to 1), to give 2 in high yields (70%-86%). The PdI2-KI catalytic system could be recycled up to six times without appreciable loss of activity. Moreover, products 2 could be easily converted in a one-pot fashion into 2-hydroxymethylbenzofurans 3 (52%-71%, based on 1) and 2-methoxymethylbenzofurans 4 (52%-80%, based on 1) by acid-catalyzed allylic isomerization or allylic nucleophilic substitution.
本文报道了一种在离子液体介质（BmimBF4）中，通过 2-（1-羟丙-2-炔基）苯酚 1 的杂环化反应，以钯催化合成 2-亚甲基-2,3-二氢苯并呋喃-3-醇 2 的可回收方法。该过程在相对温和的条件下（100°C，5 h）进行，催化量（2 mol %）的 PdI2 与 KI（相对于 PdI2 为 5 当量）和有机碱，如吗啉（相对于 1 为 1 当量）一起使用，可以以高收率（70%-86%）得到 2。PdI2-KI 催化体系可以回收使用六次而活性没有明显损失。此外，产物 2 可以通过酸催化的烯丙基异构化或烯丙基亲核取代，很容易一锅法转化为 2-羟甲基苯并呋喃 3（基于 1 的 52%-71%）和 2-甲氧基甲基苯并呋喃 4（基于 1 的 52%-80%）。
