We have developed a Brønsted acid-catalyzed 1,8-conjugate addition/3,3-rearrangement between propargylic p-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.
Chen et al. (Fri,) studied this question.