Controllable Synthesis of Polyheterocyclic Spirooxindoles and 3,3-Bistryptophol Oxindoles via Fe(ClO4)3 . 6H2O-Promoted Hetero-Pictet-Spengler Reaction

An efficient Fe(ClO4)(3) . 6H(2)O-promoted hetero-Pictet-Spengler reaction has been developed, enabling divergent approaches to plenty of structurally diverse polyheterocyclic spirooxindoles and 3,3-bistryptophol oxindoles from readily available isatins and substituted aromatic heterocyclic derivatives in up to 98% yield. Mechanistic investigation reveals that the perchloric acid generated upon on hydrolysis of Fe(ClO4)(3) . 6H(2)O by residual water was the real catalyst. The synthetic robustness of this transformation is demonstrated by the friendly, easy handling of the catalyst and the controllable access of diverse privileged heterocyclic skeletons.