Chiral Iron Porphyrins Catalyze Enantioselective Intramolecular C(sp³)−H Bond Amination Upon Visible‐Light Irradiation

Abstract

Iron‐catalyzed asymmetric amination of C(sp3)−H bonds is appealing for synthetic applications due to the biocompatibility and high earth abundance of iron, but examples of such reactions are sparse. Herein we describe chiral iron complexes of meso‐ and β‐substituted‐porphyrins that can catalyze asymmetric intramolecular C(sp3)−H amination of aryl and arylsulfonyl azides to afford chiral indolines (29 examples) and benzofused cyclic sulfonamides (17 examples), respectively, with up to 93 % ee (yield: up to 99 %) using 410 nm light under mild conditions. Mechanistic studies, including DFT calculations, for the reactions of arylsulfonyl azides reveal that the Fe(NSO2Ar) intermediate generated in situ under photochemical conditions reacts with the C(sp3)−H bond through a stepwise hydrogen atom transfer/radical rebound mechanism, with enantioselectivity arising from cooperative noncovalent interactions between the Fe(NSO2Ar) unit and the peripheral substituents of the chiral porphyrin scaffold.

Enantioselective and Enantioconvergent Iron‐Catalyzed C(sp3)‐H Aminations to Chiral 2‐Imidazolidinones

“…Che and coworkers recently disclosed iron‐porphyrin‐catalyzed enantioselective ring‐closing C(sp 3 )‐H aminations of aryl azides and arylsulfonyl azides upon visible light irradiation. [ 32 ] The here presented work contributes to the handful of recent examples on iron‐catalyzed enantioselective nitrene‐ mediated C(sp 3 )‐H aminations. The use of an iron catalyst with a chiral tetradentate N4‐ligand is noteworthy because this type of catalyst is very well established for catalyzing asymmetric C—H and C=C oxidations [ 17‐21 ] but not for C—H aminations as revealed in this work and our two previous studies.…”

Protonation of Pendant Pyridine Substituents in an Iron Porphyrin Hangman Complex: Influence on Spectral Visibility and Electrocatalysis

“…10 Naturally occurring heme enzymes usually perform catalysis via oxygen binding, whereas synthetic iron porphyrins have been shown to additionally show activity in hydrogen evolution reaction (HER), 11 carbon dioxide reduction reaction (CO 2 RR), 12 or even aminations. 13 All of these reactions are not only influenced by the redox chemistry of the iron center but also by the second coordination sphere of the catalyst. 11,14 Possible influences include the additional supply (or uptake) of protons and the (de)stabilization of certain intermediates that control the course of the reaction.…”