Stereoselective Radical Amination of Electron-Deficient C(sp³)–H Bonds by Co(II)-Based Metalloradical Catalysis: Direct Synthesis of α-Amino Acid Derivatives via α-C–H Amination

Abstract

The cobalt(II) complex of 3,5-DitBu-IbuPhyrin, [Co(P1)], is an effective catalyst for intramolecular amination of electron-deficient C–H bonds, including those adjacent to electron-withdrawing CO2R, C(O)NR2, C(O)R, and CN groups, in excellent yields with high regio- and stereoselectivity. The [Co(P1)]-catalyzed amination system provides a direct method for the synthesis of α-amino acid derivatives from the corresponding carboxylate precursors.

Characterization of Porphyrin-Co(III)-‘Nitrene Radical’ Species Relevant in Catalytic Nitrene Transfer Reactions

“…4 Given the ubiquity of nitrogen atoms in biologically active compounds, 8 nitrene transfer reactions also have very important applications in making molecules of interest. However, the applicability of metal-nitrenoids has so far been limited to alkene aziridination, 9,10 C–H amination 11,12 and amidation. 13 …”

“…Thus, well-studied complexes with redox active aminyl ligand radicals are limited to only a few well-characterized examples, 65 and related complexes bearing redox non-innocent nitrene ligands are even scarcer. 9,43,65–67 Given the importance of these radicaloid nitrene species in metal-catalyzed nitrene transfer and C–H functionalization reactions, 10,12,13,39–42,68 we gathered more experimental evidence for the formation of the previously reported mono-nitrene radical complexes upon reaction of cobalt(II) porphyrins with nitrene transfer reagents. 9,43 Furthermore, we here reveal the first example of a bis-nitrene species of 1 P1 upon reacting the stronger oxidizing nitrene transfer agent N -nosyl iminoiodane 4 Ns with 1 P1 .…”

Comparative Study of the Catalytic Amination of Benzylic C–H Bonds Promoted by Ru(TPP)(py)2 and Ru(TPP)(CO)

“…They are also efficient in the amination of benzylic C-H bonds in the α or β positions with respect to an ester group to yield the corresponding and biologically relevant α-and β-amino esters. [23,[31][32][33] One of the most extensively used amination catalyst is the five-coordinate complex Ru(TPP)(CO) (1) (TPP = dianion of tetraphenylporphyrin), which has the π-acceptor CO ligand in the axial position. The vacant coordination site in the trans position is suitable for azide activation.…”

Efficient synthesis of 2-arylquinazolines via copper-catalyzed dual oxidative benzylic CH aminations of methylarenes

“…In these syntheses, the key step is to construct C-N bonds of the cyclization. Recently, transition-metal-catalyzed oxidative aminations of sp 3 C-H bond have emerged as important methods for C-N bond formations because of short steps and atom-economical advantages [21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38]. In particular, copper as an inexpensive and lowly toxic metal catalyst, has been employed to catalyze the formation of C-N bond via a sp 3 C-H amination [39][40][41][42][43][44][45][46][47][48][49].…”