Access to Fused Indolines with a Quaternary <i>N</i> , <i>N</i> ′-Aminal Center: Aza-Wacker-Type Cyclization for a Telescoped Reaction Sequence

A highly efficient one-pot sequence has been developed for the rapid construction of fused polycyclic indolines bearing a C2-<i>N,N</i>'-aminal quaternary center. The process, which employs 1,2-diaza-1,3-dienes and 2-substituted indoles as key substrates, proceeds through a Zn(II)-catalyzed Michael addition, followed by an intramolecular Cu(II)-catalyzed dearomative oxidative cyclization. This sequence enabling N-C(sp²) bond formation via formal C(sp²)-H activation, azoalkene addition, and aza-Wacker-type cyclization exhibits broad substrate tolerance and delivers unprecedented tricyclic indole architectures (namely 9a-substituted 9,9a-dihydro-1<i>H</i>-pyridazino[3,4-<i>b</i>]indoles) in good to excellent yields.