Convenient Synthesis and Molecular Structures of Diverse Functionalized Polycyclic Spirooxindoles

The diverse functionalized polycyclic spirooxindoles were efficiently synthesized by base promoted cyclization reaction of cyclic β ‐enamino esters and MBH carbonates of isatins. Three kinds of MBH carbonates of isatins showed very different reactivity and gave different kinds of polycyclic compounds. A very interesting ring contraction process from six‐membered 3,4‐dihydrobenzo[ b ][1,4]oxazine to 5‐membered 2,3‐dihydrobenzo[ d ]oxazole on spirooxindole skeleton was clearly observed. The relative configurations of the various polycyclic compounds were clearly elucidated by determining several single‐crystal structures.