Iron complexes of tetramine ligands catalyse allylic hydroxyamination via a nitroso–ene mechanism

Abstract

SummaryIron(II) complexes of the tetradentate amines tris(2-pyridylmethyl)amine (TPA) and N,N′-bis(2-pyridylmethyl)-N,N′-dimethylethane-1,2-diamine (BPMEN) are established catalysts of C–O bond formation, oxidising hydrocarbon substrates via hydroxylation, epoxidation and dihydroxylation pathways. Herein we report the capacity of these catalysts to promote C–N bond formation, via allylic amination of alkenes. The combination of N-Boc-hydroxylamine with either FeTPA (1 mol %) or FeBPMEN (10 mol %) converts cyclohexene to the allylic hydroxylamine (tert-butyl cyclohex-2-en-1-yl(hydroxy)carbamate) in moderate yields. Spectroscopic studies and trapping experiments suggest the reaction proceeds via a nitroso–ene mechanism, with involvement of a free N-Boc-nitroso intermediate. Asymmetric induction is not observed using the chiral tetramine ligand (+)-(2R,2′R)-1,1′-bis(2-pyridylmethyl)-2,2′-bipyrrolidine ((R,R′)-PDP).

Intramolecular Pd-Catalyzed Reductive Amination of Enolizable sp3-C–H Bonds

“…This challenge has encouraged the development of methods to generate nitrosoarenes in situ from readily accessible precursors. While it is possible to access nitrosoarenes through the oxidation of N -hydroxyanilines, most efforts have focused on their reductive generation from nitroarenes . Using nitroarenes as precursors to nitrosoarenes is an attractive synthetic strategy, since these compounds are benchtop stable, the nitro group is easy to install, and many examples are commercially available.…”