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

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 (BmimBF(4)) is presented. The process takes place under relatively mild conditions (100 °C, 5 h) in the presence of catalytic amounts (2 mol %) of PdI(2) in conjunction with KI (5 equiv with respect to PdI(2)) and an organic base, such as morpholine (1 equiv with respect to 1), to give 2 in high yields (70%–86%). The PdI(2)-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.