C-H Functionalization by Copper-Catalyzed Vinyl Nitrene Transfer

Abstract

Copper-catalyzed nitrene transfer reactions including aziridination of alkenes and amination of C-H bonds are among the appealing methods of C-N bond formation in organic syntheses. In the literature, these copper-catalyzed reactions are mainly focused on the transfer of sulfonyl nitrenes;1 reports on the transfer of other types of nitrenes by copper catalysis are sparse. Vinyl nitrene transfer catalyzed by copper was recently proposed for three-component synthesis of 1,2,3-triazole derivatives, which proceeds through vinyl nitrene insertion into Cu-C bond.2 On the other hand, the nitrene sources used in copper catalysis are iminoiodanes in most of the literature reports, with limited cases in which organic azide nitrene sources were employed. We are interested in developing novel nitrene transfer reactions mediated by transition metals, including C-H functionalization and mechanistic studies.3 Following our previous studies in this area using ruthenium porphyrins,4 we turned our attention to metal complexes with tripodal S-ligands, which have rarely been employed in nitrene transfer chemistry. We have found that copper(II) complexes of these tripodal S-ligands are highly selective catalysts for nitrene transfer reactions. Notably, with a series of vinyl azides as nitren source, the copper-catalyzed reactions resulted in intramolecular vinyl nitrene insertion into C-H bonds to afford amination products in up to 98% yields.