Reaction Conditions-Dependent Divergent Synthesis of Spirooxindoles and Bisoxindoles

The ability to access structurally diverse and complex compounds efficiently and economically from readily available starting materials is an important goal in organic synthesis and medicinal chemistry. Herein, DABCO-catalyzed reactions between isatin-derived MBH carbonates and 3-formylchromones selectively leading to either benzopyrone fused spirocyclopentene oxindoles or spirocyclopentadiene 2-oxindole incorporating a 2-hydroxybenzoyl moiety are described. Interestingly, in the absence of 3-formylchromones, the first synthesis of bisoxindoles containing highly functionalized tri- and tetra-substituted alkene groups can be achieved using the same catalytic system. In this case, the in situ generated tert-butyl carbonate anion (BocO-), which is usually produced as a precursor to the tert-butoxide anion (tBuO-) or as waste, could be finely merged into the products as an efficient nucleophilic partner. Importantly, this tunable approach not only represents a rare example of isatin-derived MBH carbonate-based α-regioselective [3 + 2] annulations, but also constitutes the first intermolecular allylic alkylation reaction between two isatin-derived MBH carbonate molecules.