Synthesis of 2‑Amino-3-hydroxy‑3<i>H</i>‑indoles via Palladium-Catalyzed One-Pot Reaction of Isonitriles, Oxygen, and <i>N</i>‑Tosylhydrazones Derived from 2‑Acylanilines

Abstract

A cyanide-free one-pot procedure was developed to access 2-amino-3-hydroxy-3<i>H</i>-indoles, which involved: (1) <i>in situ</i> formation of ketenimines by the reaction of <i>N</i>′-(1-(2-amino­phenyl)­ethylidene)-<i>p</i>-tosyl­hydrazones with isonitriles; (2) the intramolecular nucleophilic attack of ketenimines by the amino in phenyl furnishing the ring closure leading to 2-aminoindoles; (3) the oxidation of 2-aminoindoles by O₂ leading to 2-amino-3-hydroxy-3<i>H</i>-indoles. This strategy represents not only a key compliment to the sporadic synthetic methods toward 2-amino-3-hydroxy-3<i>H</i>-indoles but also progress in <i>N-</i>tosylhydrazone, isonitrile, and ketenimine chemistry