Metal-Free, Mild, Nonepimerizing, Chemo- and Enantio- or Diastereoselective N‑Alkylation of Amines by Alcohols via Oxidation/Imine–Iminium Formation/Reductive Amination: A Pragmatic Synthesis of Octahydropyrazinopyridoindoles and Higher Ring Analogues
journal contributionposted on 06.12.2013, 00:00 by Imran A. Khan, Anil K. Saxena
A mild step and atom-economical nonepimerizing chemo- and enantioselective N-alkylating procedure has been developed via oxidation/imine–iminium formation/reduction cascade using TEMPO–BAIB–HEH–Brønsted acid catalysis in DMPU as solvent and a stoichiometric amount of amine. The optimized conditions were further extended for the nonenzymatic kinetic resolution of the chiral amine thus formed under nonenzymatic in situ hydrogen-transfer conditions using VAPOL-derived phosphoric acid (VAPOL-PA) as the Brønsted acid catalyst. The enantioselective cascade of the presented reaction was successfully utilized in the synthesis of octahydropyrazinopyridoindole and its higher ring analogues.