Unexpected Copper-Catalyzed Cascade Reaction of 1,6-Enynes with Sulfoxonium Ylides

An unprecedented copper-catalyzed cascade reaction of 1,6-enynes with sulfoxonium ylides is reported, providing a series of structurally intriguing 2,3-disubstituted indolines bearing a conjugated dienone functionality at the 3-position in moderate to excellent yields with good chemo-, regio-, and diastereoselectivities under mild reaction conditions. Importantly, sulfoxonium-ylide-derived copper-carbene herein exhibits quite different reactivity from that of diazo copper-carbene. A rational mechanism, an initial ammonium ylide rather than allene formation, is proposed.