Mechanistic Studies on the Synthesis of Pyrrolidines and Piperidines via Copper-Catalyzed Intramolecular C–H Amination

We have recently developed a method for the synthesis of pyrrolidines and piperidines via intramolecular C–H amination of N-fluoride amides using [TpxCuL] complexes as precatalysts [Tpx = tris­(pyrazolyl)­borate ligand and L = THF or CH3CN]. Herein, we report mechanistic studies on this transformation, which includes the isolation and structural characterization of a fluorinated copper­(II) complex, [(TpiPr2OH)­CuF] [TpiPr = hydrotris­(3,5-diisopropylpyrazolyl)­borate], pertinent to the mechanistic pathway. The effects of the nature of the Tpx ligand in the copper catalyst as well as of the halide in the N–X amides employed as reactants have been investigated both from experimental and computational perspectives.