Carbon–Nitrogen Bond Formation Through Cross-Dehydrogenative Coupling Reactions

Abstract

There are many methods available in the synthetic toolbox to construct carbon–nitrogen bonds, but these standardly require preactivation of the substrate. These involve classical, nonmetal catalyzed methods (e.g., nucleophilic substitutions) and catalytic methods (e.g., the Ullmann condensation reaction) as well as modern metal-catalyzed approaches with wide scope (Buchwald–Hartwig reaction, hydrogen-borrowing reactions). Cross-dehydrogenative couplings (CDCs) couple a C–H with an N–H bond and do not require any preactivation and are therefore considered the “nec plus ultra” in amination chemistry. Based on the ubiquitous nature of C–H bonds in substrates and the wide availability of amines as reactants they inherently show great application potential. Especially from a sustainable chemistry point of view it holds great promise, provided green oxidants can be used in a safe manner. However, though major advances have been made in the field, this last addition to the carbon–nitrogen bond forming toolbox is still in its infancy. The major investigations and advances dealing with CDCs for C–N bond formation since 2014 are summarized in this review. Intra- and intermolecular direct oxidative amination reactions on C(sp2)–H as well as C(sp3)–H bonds are included. Both metal-catalyzed and metal-free approaches are covered, as well as the corresponding mechanistic proposals.