Rhodium(ii)-catalyzed C–H aminations using N-mesyloxycarbamates: reaction pathway and by-product formation

Abstract

N-Mesyloxycarbamates are practical nitrene precursors that undergo C–H amination reactions in the presence of rhodium dimer catalysts. Under these conditions, both oxazolidinones and chiral amines have been prepared in a highly efficient manner. Given the elevated reactivity of the intermediates involved in the catalytic cycle, mechanistic details have remained hypothetical, relying on indirect experiments. Herein a density functional theory (DFT) study is presented to validate the catalytic cycle of the rhodium-catalyzed C–H amination with N-mesyloxycarbamates. A concerted pathway involving Rh–nitrene species that undergoes C–H insertion is found to be favored over a stepwise C–N bond formation manifold. Density functional calculations and kinetic studies suggest that the rate-limiting step is the C–H insertion process rather than the formation of Rh–nitrene species. In addition, these studies provide mechanistic details about competitive by-product formation, resulting from an intermolecular reaction between the Rh–nitrene species and the N-mesyloxycarbamate anion.