Synthesis of Functionalized Benzofurans via Pd-Catalyzed Cycloisomerization

Significance

Reported is a Pd-catalyzed cyclo­isomerization of 2-(1-hydroxyprop-2-ynyl)phenols to afford 2-methylene-2,3-dihydrobenzofuran-3-ols in very good yields. The reaction conditions were extensively screened and other metal ­sources, such as AuCl and CuCl₂, function as well albeit in lower yields. The products were further isomerized to 2-hydroxymethylbenzofurans (acid- catalyzed) or converted into 2-alkoxymethylbenzofurans (nucleophilic allylic substitution with alcohols). Both steps proceed in good to very good yields. Substrate scope was well studied and three plausible alternate mechanisms were suggested without evidence.