Dearomative 1,6-enyne cycloisomerization of alkyne-tethered benzofurans and indoles via a 6-endo-dig cyclization

Abstract

A palladium-catalyzed dearomative 1,6-enyne cycloisomerization of C2- or C3-alkyne-tethered benzofurans and C2-alkyne-tethered indoles has been developed via a 6-endo-dig cyclization. By employing Pd(OAc)₂ as a catalyst, an array of spiro dihydrobenzofurans and indolines were afforded in air with moderate to high yields. This protocol features 100% atom economy and high regioselectivity. A deuterium experiment and Hammett plot analysis provide insights into a possible dearomative electrophilic cyclization mechanism.