Chemoselective silver-catalyzed nitrene insertion reactions

Scamp, Ryan J.; Rigoli, Jared W.; Schomaker, Jennifer M.

doi:10.1515/pac-2014-5040

Cited by 43 publications

(21 citation statements)

References 11 publications

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“…Our group has reported tunable, chemo‐ and site‐selective nitrene transfers catalyzed by silver(I) complexes supported by diverse N‐chelating ligands . We wondered if the flexibility exhibited by these catalysts might improve both the scope and the ee value of intramolecular alkene and allene aziridinations.…”

Section: Methodsmentioning

confidence: 99%

Chemo‐ and Enantioselective Intramolecular Silver‐Catalyzed Aziridinations

Weatherly

Guzei

et al. 2017

Angew Chem Int Ed

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Asymmetric nitrene transfer reactions are a powerful tool for the preparation of enantioenriched amine building blocks. Herein, we report chemo- and enantioselective silver-catalyzed aminations that transform di- and trisubstituted homoallylic carbamates into [4.1.0]-carbamate-tethered aziridines in good yields and ee up to 92%. The effects of the substrate, silver counteranion, ligand, solvent and temperature on both chemoselectivity and ee were explored to complement the scope of traditional metal-catalyzed nitrene transfer reactions. Stereochemical models were proposed to rationalize the observed absolute stereochemistry of the aziridines, which undergo nucleophilic ring-opening to yield enantioenriched amines with no erosion in stereochemical integrity.

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Section: Methodsmentioning

confidence: 99%

Chemo‐ and Enantioselective Intramolecular Silver‐Catalyzed Aziridinations

Weatherly

Guzei

et al. 2017

Angew Chem Int Ed

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“…The Schomaker group has reported silver-catalyzed nitrene transfer reactions that override substrate control to achieve nondirected and tunable intramolecular aminations . For example, catalysts 1 and 2 , based on AgOTf and 1,10-phenanthroline (phen) (Scheme ), enable selective aziridination or C–H amination of homoallylic and homoallenic carbamates, , where the reaction outcome is controlled by simply varying the ligand to AgOTf ratio.…”

Section: Introductionmentioning

confidence: 99%

Catalyst-Controlled Nitrene Transfer by Tuning Metal:Ligand Ratios: Insight into the Mechanisms of Chemoselectivity

et al. 2017

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Catalyst-controlled, selective nitrene transfer is often challenging when both C−H and CC bonds are present in a substrate. Interestingly, a simple change in the Ag(I):L ratio (L = bidentate N,N-donor ligand) enables tunable, chemoselective nitrene transfer that favors either C C bond aziridination using an ∼1:1 Ag:L ratio (AgLOTf) or insertion into a C−H bond when the Ag:L ratio in the catalyst is 1:2 (AgL 2 OTf). In this paper, mechanistic studies, coupled with kinetic profiling of the entire reaction course, are employed to examine the reasons for this unusual behavior. Steady-state kinetics were found to be similar for both AgLOTf and AgL 2 OTf; both complexes yield electronically similar reactive intermediates that engage in nitrene transfer involving formation of a short-lived radical intermediate and barrierless radical recombination. Taken together, experimental and computational studies point to two effects that control tunable chemoselectivity: suppression of aziridination as the steric congestion around the silver center is increased in AgL 2 OTf and a decrease in the rate of C−H insertion with AgLOTf in comparison to AgL 2 OTf. The observation that the sterics of Ag catalysts can be varied, with minor effects on the electronic features of the putative nitrene, has important implications for the development of other silver catalysts that enable tunable, site-selective C−H bond aminations.

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“…Aziridines are important synthetic intermediates in organic synthesis, medicinal chemistry, and polymer chemistry, Catalytic approaches to their syntheses have rapidly expanded in recent years , . Transition metal‐catalyzed reactions involving nitrene transfer to alkenes have gained prominence in this regard , . Of these latter catalysts, copper(I) and silver(I) scorpionate complexes [tris(pyrazolyl)borates, (normal scorpionates, or Tp R , Scheme , top left), tris(pyrazolyl)methanes (Tpm R or C ‐scorpionates, Scheme , top right), certain C‐heteroscorpionates (Scheme , bottom left), and certain nitrogen‐confused C‐scorpionates (Scheme , bottom right)] have proven adept at catalytically affording aziridines from alkenes and various nitrene sources under mild conditions.…”

Section: Introductionmentioning

confidence: 99%

Silver(I) and Copper(I) Complexes of Semi‐Bulky Nitrogen‐Confused C‐Scorpionates

et al. 2020

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Two new sterically demanding nitrogen-confused C-scorpionate ligands with a bis(3,5-diisopropylpyrazol-1yl)methyl group bound to the 3-position of a normal pyrazole ( H L iPr2 ) or an N-toluenesulfonyl pyrazole ( Ts L iPr2 ) have been prepared. Reactions between the ligands ( x L iPr2 ) and silver trifluoromethanesulfonate, AgOTf, gave four new compounds of the types [Ag(Ts, 1b; x = H, 2b) depending on the initial metal:ligand ratio. Similarly, the reactions with [Cu(CH 3 CN) 4 ](PF 6 ) produce [a] Dr.to trap and spectroscopically characterize the nitrene intermediates {[(2-py)Bpm R3R5 ]Cu(NTs)} + in CH 2 Cl 2 at -78°C using (2-tBuSO 2 )C 6 H 4 I=NTs [34] as a soluble nitrene source. The spectroscopic and magnetic data were consistent with diamagnetic, singlet species at -78°C. Calculations showed ground state triplet but all spin states [ 1/3 Cu I -nitrene or 1/3 Cu II -N·(iminyl)] and nitrene binding modes (κ 1 N-, κ 2 N,O-) are thermally accessible. These intermediates were capable of stoichiometrically transferring a nitrene unit to a variety of substrates. Then, different {[(2-py)Bpm R3R5 ]Cu(CH 3 CN)}(PF 6 ) complexes were found to be capable catalysts for nitrene transfer to unsubstituted or p-substituted styrenes giving modest yields (> 65 %) of aziridine under mild ocnditions (PhI=NTs/CH 2 Cl 2 /295 K, 24 h).In a previous study, [27] eight complexes of the type [Ag( x L R ) n ](OTf ) (n = 1, 2 and x L R = H L, Ts L, H L*, and Ts L*) were characterized and evaluated for their ability to catalyze aziridination of styrene. Both ESI(+) MS and NMR spectroscopic studies indicated that the analytically pure [Ag( x L R ) n ](OTf ) compounds did not retain their structure in CH 3 CN rather were involved in multiple dynamic equilibria in solution. These dynamic processes remained in the fast exchange regime on the NMR timescale down to the freezing point of the solvent, thereby obfuscating structural information. These silver complexes of nitrogen-confused C-scorpionates showed no or very little capacity to participate in styrene aziridination using PhI= NTs in room temperature CH 2 Cl 2 . However, [Ag( x L R ) n ](OTf ) showed modest catalytic activity at 80°C in CH 3 CN when employing a nitrene generated in-situ from H 2 NTs and PhI(OAc). Interestingly, the bulkiest derivative [Ag( Ts L * ) 2 ](OTf ) was reported to have the highest activity giving 34 % yield of the desired N-tosyl aziridine. This observation prompted the current study to determine if further increasing steric bulk of the ligands would lead to an increase in catalytic activity of silver complexes. Herein we report on the preparation of two new semi-bulky nitrogen confused scorpionates, Ts L iPr2 and H L iPr2 and their silver(I) and copper(I) complexes. The copper(I) complexes were prepared to compare catalytic activity with their silver congeners, and possibly to demonstrate the generality of any trends in ligand sterics on catalytic activity. It was also hoped that the slower ligand exchange rates associated with the smaller copper(I) compared ...

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Chemoselective silver-catalyzed nitrene insertion reactions

Cited by 43 publications

References 11 publications

Chemo‐ and Enantioselective Intramolecular Silver‐Catalyzed Aziridinations

Chemo‐ and Enantioselective Intramolecular Silver‐Catalyzed Aziridinations

Catalyst-Controlled Nitrene Transfer by Tuning Metal:Ligand Ratios: Insight into the Mechanisms of Chemoselectivity

Silver(I) and Copper(I) Complexes of Semi‐Bulky Nitrogen‐Confused C‐Scorpionates

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