A Recyclable Palladium-Catalyzed Synthesis of 2-Methylene-2,3-Dihydrobenzofuran-3-ols by Cycloisomerization of 2-(1-Hydroxyprop-2-ynyl)phenols in Ionic Liquids
作者:Raffaella Mancuso、Bartolo Gabriele
DOI:10.3390/molecules180910901
日期:——
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.
本文介绍了在离子液体介质(BmimBF4)中通过 2-(1-羟基丙-2-炔基)苯酚 1 的杂环合成 2-亚甲基-2,3-二氢苯并呋喃-3-醇 2 的可循环钯催化合成方法。该过程是在相对温和的条件下(100 °C,5 小时),在催化量(2 摩尔%)的 PdI2 与 KI(相对于 PdI2 为 5 等份)和有机碱(如吗啉,相对于 1 为 1 等份)的存在下进行的,从而得到高产率(70%-86%)的 2。PdI2-KI 催化系统可循环使用多达六次,而不会明显丧失活性。此外,通过酸催化的烯丙基异构化或烯丙基亲核取代,产物 2 可以很容易地以一锅方式转化为 2-羟甲基苯并呋喃 3(52%-71%,以 1 为基准)和 2-甲氧基甲基苯并呋喃 4(52%-80%,以 1 为基准)。