Copper-Catalyzed Cascade Coupling/Cyclization/Switchable aza-Claisen Rearrangement for Indole Skeletons

A copper-catalyzed cascade coupling/cyclization/switchable aza-Claisen rearrangement was disclosed for the first time, realizing the divergent synthesis of 2,3-disubstituted, C3-allylated, or C2-but-3-en-1-ylated indole derivatives from N-allyl-2 alkynylanilines and diazo compounds. Compared to previous works, the application of diazo compounds as coupling partners significantly expanded the variety of functional groups on the C2 position. Importantly, a catalytic amount of organic base, triethylamine, was found to act as a chemical switch to govern two different aza-Claisen rearrangement pathways.