Construction of Hydrodibenzo[b,d]furan Frameworks from Morita–Baylis–Hillman Carbonates of Isatins and o-Hydroxy Enones via Palladium and Brønsted Base Relay Catalysis

A cascade assembly between isatin-derived Morita–Baylis–Hillman carbonates and o-hydroxybenzylideneacetones has been developed under the relay catalysis of Pd(PPh3)4 and DBU, affording a spectrum of 1,2,3,4-tetrahydrodibenzo[b,d]furan architectures incorporating a spirooxindole motif in moderate to good yields with excellent diastereoselectivity. The fused indole analogues were similarly furnished by employing the benzylideneacetones having an o-TsNH group.