Reductive Amination by Photoredox Catalysis and Polarity‐Matched Hydrogen Atom Transfer

Guo, Xingwei; Wenger, Oliver S.

doi:10.1002/anie.201711467

Cited by 92 publications

(81 citation statements)

References 29 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The simplicity, selectivity, near‐quantitative isotope substitution (as opposed to other methods in the literature), and potentially large number of substrates that can be dechlorinated by

e_{aq}^{• -}

could make this an attractive method for deuteration and—with no changes in mechanism expected—tritiation, which is of importance for investigations of pharmaceuticals . Using

e_{aq}^{• -}

as mediator seems to obviate the necessity of polarity matching by adding a thiol: with the mechanism of this work, the ascorbate species efficiently serve as both the electron and the hydrogen‐isotope donors in these photoredox‐driven atom transfers …”

Section: Resultsmentioning

confidence: 92%

Micellized Tris(bipyridine)ruthenium Catalysts Affording Preparative Amounts of Hydrated Electrons with a Green Light‐Emitting Diode

Naumann

Lehmann

Goez

2018

Chemistry A European J

View full text Add to dashboard Cite

We have explored alkyl substitution of the ligands as a means to improve the performance of the title complexes in photoredox catalytic systems that produce synthetically useable amounts of hydrated electrons through photon pooling. Despite generating a super-reductant, these electron sources only consume the bioavailable ascorbate and are driven by a green light-emitting diode (LED). The substitutions influence the catalyst activity through the interplay of the quenching parameters, the recombination rate of the reduced catalyst OER and the ascorbyl radical across the micelle-water interface, and the quantum yield of OER photoionization. Laser flash photolysis yields comprehensive information on all these processes and allows quantitative predictions of the activity observed in LED kinetics, but the latter method provides the only access to the catalyst stability under illumination on the timescale of the syntheses. The homoleptic complex with dimethylbipyridine ligands emerges as the optimum that combines an activity twice as high with an undiminished stability in relation to the parent compound. With this complex, we have effected dehalogenations of alkyl and aryl chlorides and fluorides, hydrogenations of carbon-carbon double bonds, and self- as well as cross-coupling reactions. All the substrates employed are impervious to ordinary photoredox catalysts but present no problems to the hydrated electron as a super-reductant. A particularly attractive application is selective deuteration with high isotopic purity, which is achieved simply by using heavy water as the solvent.

show abstract

“…The simplicity, selectivity, near‐quantitative isotope substitution (as opposed to other methods in the literature), and potentially large number of substrates that can be dechlorinated by

e_{aq}^{• -}

could make this an attractive method for deuteration and—with no changes in mechanism expected—tritiation, which is of importance for investigations of pharmaceuticals . Using

e_{aq}^{• -}

Section: Resultsmentioning

confidence: 92%

Micellized Tris(bipyridine)ruthenium Catalysts Affording Preparative Amounts of Hydrated Electrons with a Green Light‐Emitting Diode

Naumann

Lehmann

Goez

2018

Chemistry A European J

View full text Add to dashboard Cite

show abstract

“…[1] This methodology allows single-electron transfer (SET) to replace the conventional two electron transfer process by using photoredox and transition metal dual-catalytic systems,t hus significantly reducing the barrier for each step in crosscoupling reactions. Av ariety of primary,s econdary,a nd tertiary alkylb romides are activated by the photoexcited palladium metal catalyst to provide aseries of olefins at room temperature under mild reaction conditions.Mechanistic investigations and density functional theory (DFT) studies suggest that ap hotoinduced inner-sphere mechanism is operative in whichabarrierless,single-electron transfer oxidative addition of the alkyl halide to Pd 0 is key for the efficient transformation.…”

mentioning

confidence: 99%

mentioning

confidence: 99%

Oxidative Addition to Palladium(0) Made Easy through Photoexcited‐State Metal Catalysis: Experiment and Computation

et al. 2019

View full text Add to dashboard Cite

Visible-light induced, palladium catalyzeda lkylations of a,b-unsaturated acids with unactivated alkyl bromides are described. Av ariety of primary,s econdary,a nd tertiary alkylb romides are activated by the photoexcited palladium metal catalyst to provide aseries of olefins at room temperature under mild reaction conditions.Mechanistic investigations and density functional theory (DFT) studies suggest that ap hotoinduced inner-sphere mechanism is operative in whichabarrierless,single-electron transfer oxidative addition of the alkyl halide to Pd 0 is key for the efficient transformation.Cross-coupling reactions are one of the most important synthesis tools for the formation of C À Co rC-heteroatom bonds.C onventionally,t hree key steps are involved in the cross-coupling reaction:o xidative addition, transmetalation, and reductive elimination. Often challenges arise in the individual steps,d epending on the coupling partners,m etal catalysts or reaction conditions employed. In recent decades, numerous catalysts,aswell as ligands,have been developed in order to reduce the energy barrier in the bond-forming and breaking steps.More recently,ithas been shown that visiblelight enhances cross-couplings employing radicals. [1] This methodology allows single-electron transfer (SET) to replace the conventional two electron transfer process by using photoredox and transition metal dual-catalytic systems,t hus significantly reducing the barrier for each step in crosscoupling reactions. [2] Despite developments made in crosscoupling chemistry,t he conventional oxidative addition of alkyl electrophiles to Pd 0 remains sluggish, even at elevated temperature,o wing to the electron-rich nature of the alkyl halide bond. [3] In fact, computational studies have revealed that the alkyl bromide oxidative addition to Pd 0 is endothermic with ah igh energy barrier of 41.6 kcal mol À1 .F urther, alkyl-palladium(II) species that are formed through at wo-electron transfer are considerably less stable because of the lack of p-electrons interacting with the empty d-orbitals of the metal. This results in fast b-hydride (b-H) elimination from salkyl-palladium(II) intermediates which outcompetes the required olefin insertion in decarboxylative alkylation crosscoupling reactions. [3,4] In contrast to the photoredox dual-catalysis strategy which promotes cross-coupling by lowering the energy barrier, we now report the use of am echanistically distinct, SET barrierless oxidative addition strategy for alkylation of vinylic acids,using Pd complexes as both photosensitizer and cross-coupling catalyst. [5] This lowers the oxidative addition barrier resulting in an alkyl radical and aP d I intermediate (Figure 1) which can add to an a,b-unsaturated acids. Subsequent carbon dioxide elimination provides the akylated olefin and the regenerated catalyst. To the best of our knowledge,avisible light-induced palladium catalyzed decarboxylative C(sp 3 ) À C(sp 2 )c ross-coupling alkylation has not been reported.Vinylic acids are readily available and stable,...

show abstract

“…The first method for reductive amination by photoredox catalysis was reported only very recently . The photochemical point of attack is the iminium species formed from condensation of the carbonyl and amine substrates in equilibrium (Scheme a).…”

Section: Photochemical Reductive Aminationmentioning

confidence: 99%

“…(b) Relevant bond dissociation energies (BDEs). (c) Mechanism for interception of α‐amino alkyl radicals via polarity‐matched HAT …”

Section: Photochemical Reductive Aminationmentioning

confidence: 99%

Reductive Amination and Enantioselective Amine Synthesis by Photoredox Catalysis

et al. 2019

Self Cite

View full text Add to dashboard Cite

Photochemistry usually functions on a one‐photon‐one‐electron basis, leading to unstable radical intermediates that must be intercepted rapidly to allow efficient product formation. This can render multi‐electron reductions and enantioselective reactions particularly challenging. In this minireview, we discuss recent advances in the area of photo‐driven multi‐electron transfer with a particular focus on our own work on reductive amination and the enantioselective synthesis of amines by combined photoredox and enzyme catalysis. Polarity‐matched hydrogen atom transfer (HAT) between photochemically‐generated α‐amino alkyl radicals and thiols is a key step in these reactions. A cyclic reaction network comprised of light‐driven imine reduction by an Ir‐photocatalyst and enantioselective amine oxidation by the enzyme monoamine oxidase (MAO‐N‐9) was used to obtain enantioenriched amines from imines.

show abstract

Reductive Amination by Photoredox Catalysis and Polarity‐Matched Hydrogen Atom Transfer

Cited by 92 publications

References 29 publications

Micellized Tris(bipyridine)ruthenium Catalysts Affording Preparative Amounts of Hydrated Electrons with a Green Light‐Emitting Diode

Micellized Tris(bipyridine)ruthenium Catalysts Affording Preparative Amounts of Hydrated Electrons with a Green Light‐Emitting Diode

Oxidative Addition to Palladium(0) Made Easy through Photoexcited‐State Metal Catalysis: Experiment and Computation

Reductive Amination and Enantioselective Amine Synthesis by Photoredox Catalysis

Contact Info

Product

Resources

About