Switchable construction of oxa-heterocycles with diverse ring sizes via chemoselective cyclization controlled by dibrominated compounds

The controllable synthesis of spirooxindole-fused dibenzo[ b , f ]oxocines and chromans from oxindole-embedded four-atom synthons and dibrominated compounds through, respectively, [4 + 4] and [4 + 2] cyclization reactions has been developed. In addition, the indole-fused nine-membered oxa-heterocycles also could be accessed switchably through the carbocation-rearrangement-initiated ring expansion of spirooxindole-fused dibenzo[ b , f ]oxocines by facile operation.