Relay Annulation of Ammonium Ylides with Oxindole-Derived α,β-Unsaturated Ketimines: Catalytic Construction of Spiro-polycyclic Oxindoles.

An ammonium ylide-based relay annulation was disclosed, which uses DABCO as the catalyst and oxindole-derived α,β-unsaturated ketimines and γ-bromo-crotonates as the starting materials. This method enables the rapid assembly of a series of structurally novel spiro-polycyclic oxindoles containing a bicyclo[4.1.0]heptane moiety through simultaneous generation of three new bonds and two rings in one step under mild reaction conditions.