Ligand-Controlled, Tunable Silver-Catalyzed C–H Amination

Abstract

The development of readily tunable and regioselective C–H functionalization reactions that operate solely through catalyst control remains a challenge in modern organic synthesis. Herein, we report that simple silver catalysts supported by common nitrogenated ligands can be used to tune a nitrene transfer reaction between two different types of C–H bonds. The results reported herein represent the first example of ligand-controlled and site-selective silver-promoted C–H amination.

Chemo‐ and Enantioselective Intramolecular Silver‐Catalyzed Aziridinations

“…This is not an issue in Ag catalysts with fewer open coordination sites on the metal. [12,13] Attempts to utilize [Cu(MeCN) 4 ]PF 6 with carbamates gave no reaction (entry 2), while sulfamates were successful as previously reported (entry 4). [10] These results highlight the impact of differences in metal identity and nitrogen transfer reagent on reaction behavior and point to the importance of further studies to better understand such effects.…”

“…This was surprising, as we have previously shown sulfamates to be effective in other Ag-catalyzed nitrene transfers. [12,13] Closer examination by 1 H NMR showed formation of an iminoiodinane intermediate, which eventually furnished the aziridine over a period of days (Figure S2 for details). We propose this arises from either increased Lewis acidity of Ag(I) compared to Cu(I), or more likely, the increased size of the Ag(I) cation (115–126 pm) vs. a Cu(I) ion (96 pm).…”

Metal-Catalyzed and Metal-Free Intermolecular Amination of Light Alkanes and Benzenes

“…Naturally, intramolecular versions of sp 3 and sp 2 -C–H aminations are more numerous. 94–100 Nevertheless, important issues remain unresolved, especially for light alkanes, for which C–H bond activation is frequently the turnover-limiting step. Exceptionally electrophilic metal-bound or metal-free nitrogen-donor carriers are needed to accomplish this goal, due to the strength and low polarity of the C–H bond in these unfunctionalized alkanes.…”

Silver-Mediated Direct sp3 C–H Bond Functionalization

“…The ratio of AgOTf/ligand is critical since it controlled the reaction pathways to form either aziridination or C-H insertion product. The substrate scopes were Later in 2014, ligand-controlled tunable, site-selective silver-catalyzed intramolecular amination/amidation between two different types of C-H bonds has been described by Schomaker and coworkers (Scheme 8) [30]. In the reaction, AgOTf with 4,4 0 -di-tert-butyl-2,2 0 -bipyridine ( t Bubipy) or tris(2-pyridylmethyl)amine (tpa) as the catalyst, PhIO as the oxidant, and 4 Å molecular sieves as additive were used.…”