A Versatile Tripodal Cu(I) Reagent for C-N Bond Construction via Nitrene-Transfer Chemistry: Catalytic Perspectives and Mechanistic Insights on C-H Aminations/Amidinations and Olefin Aziridinations

作者：Bagchi Vivek; Paraskevopoulou Patrina; Das Purak; Chi Lingyu; Wang Qiuwen; Choudhury Amitava; Mathieson Jennifer S; Cronin Leroy^*; Pardue Daniel B; Cundari Thomas R; Mitrikas George; Sanakis Yiannis; Stavropoulos Pericles

来源：Journal of the American Chemical Society, 2014, 136(32): 11362-11381.

DOI：10.1021/ja503869j

A Cu-I catalyst (1), supported by a framework of strongly basic guanidinato moieties, mediates nitrene-transfer from PhI=NR sources to a wide variety of aliphatic hydrocarbons (C-H amination or amidination in the presence of nitriles) and olefins (aziridination). Product profiles are consistent with a stepwise rather than concerted C-N bond formation. Mechanistic investigations with the aid of Hammett plots, kinetic isotope effects, labeled stereochemical probes, and radical traps and clocks allow us to conclude that carboradical intermediates play a major role and are generated by hydrogen-atom abstraction from substrate C-H bonds or initial nitrene-addition to one of the olefinic carbons. Subsequent processes include solvent-caged radical recombination to afford the major amination and aziridination products but also one-electron oxidation of diffusively free carboradicals to generate amidination products due to carbocation participation. Analyses of metal- and ligand-centered events by variable temperature electrospray mass spectrometry, cyclic voltammetry, and electron paramagnetic resonance spectroscopy, coupled with computational studies, indicate that an active, but still elusive, copper-nitrene (S = 1) intermediate initially abstracts a hydrogen atom from, or adds nitrene to, C-H and C=C bonds, respectively, followed by a spin flip and radical rebound to afford intra- and intermolecular C-N containing products.

• 出版日期2014-8-13