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

A cyanide-free one-pot procedure was developed to access 2-amino-3-hydroxy-3H-indoles, which involved: (1) in situ formation of ketenimines by the reaction of N′-(1-(2-amino­phenyl)­ethylidene)-p-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-3H-indoles. This strategy represents not only a key compliment to the sporadic synthetic methods toward 2-amino-3-hydroxy-3H-indoles but also progress in N-tosylhydrazone, isonitrile, and ketenimine chemistry.