1,8-Addition/[3,3]-Rearrangement in the Functionalization of Unactivated Indole C(sp ³ )–H Bonds

We have developed a Brønsted acid-catalyzed 1,8-conjugate addition/[3,3]-rearrangement between propargylic <i>p</i>-QMs and 2,3-disubstituted indoles, achieving the direct functionalization of unactivated C(sp³)-H bonds of indoles. This method provides efficient access to a series of indole derivatives bearing an all-carbon quaternary center. The resulting indole products containing an alkynyl moiety can be readily transformed to indole-fused pyridine tricycles under gold catalysis, demonstrating the synthetic utility of this methodology. The mechanism of the reaction is proposed from several control experiments.