Stereoselective construction of Bi-spirooxindole frameworks via a Michael addition/cyclization and an unexpected redox/oxidative coupling/cyclization

A series of polyheterocyclic bi-spirooxindole derivatives with skeletal diversity and molecular complexity were prepared via a cascade synthesis strategy. The key step transfer hydrogenation is smoothly fulfilled by using 3-hydroxyoxindole derivatives as the hydrogen source and the oxidative coupling happened by using simple and green molecular oxygen as the oxidant. The plausible mechanisms for the unexpected redox/oxidative coupling/cyclization were also given.