Lithium salt activated radical–radical cross‐coupling reactions of amines and carbonyls; DMAP=4‐(dimethylamino)pyridine. Figure 2. On the Pd and Pt surfaces, CO formation is observed from dissociative adsorption and decarbonylation upon benzaldehyde introduction, suggesting surface adsorbate instability under reducing conditions. We report a strategy for net redox-neutral generation and reaction of ketyl radicals. Finally, protonation of 35 produces target 1,2‐amino alcohol 30 as the major diastereomer. Next, 8 and 9 go through an asymmetric radical–radical cross‐coupling reaction to afford iridium‐complex‐bound 1,2‐diamino alcohol 10. We are grateful to the National Natural Science Foundation of China (grant nos. Ketyls react quickly with the water and with oxygen. By continuing you agree to the use of cookies. Chemistry. (2013) and M.Sc. Org Lett. Abstract. Jianyang Dong obtained his B.Sc. Cyclopropylamine radical 76 then undergoes ring cleavage to generate radical 77, which subsequently couples with ketyl radical 72 to produce imine intermediate 78. 0 comentarii. (Scheme 13).36 Hantzsch ester acts as both an electron/proton donor and an activator in this reaction. Journal of the American Chemical Society. -Aryl tetrahydroisoquinolines Initiated by Electron Donor–Acceptor Complexes Enantioselective 1,2-Addition of α-Aminoalkyl Radical to Aldehydes via Visible-Light Photoredox Initiated Chiral Oxazaborolidinium Ion Catalysis. The method for drying, while popular in some laboratories, is inferior in terms of safety and effectiveness relative to molecular sieves. Then, quinuclidinium radical cation 144 abstracts a hydrogen atom from the α‐hydroxy group of alcohol 141, which is activated by hydrogen bonding of TBAP, to produce ketyl radical 146; this occurs along with the formation of quinuclidinium ion 145. DMA=dimethylacetamide. In 2015, Macmillan and co‐workers realized the construction of γ‐lactones through the photocatalytic reaction of various alcohols with methyl acrylates (Scheme 20).43 Tetra‐n‐butylammonium phosphate (TBAP) seems to be the hydrogen‐bonding catalyst that induces HAT under the cooperation of quinuclidine as a HAT catalyst. Benzophenone is a common photosensitizer in photochemistry. 2016 Aug 16;49(8):1546-56. doi: 10.1021/acs.accounts.6b00272. Figure 2. You have 10 minutes for 6 questions. Reduction of *IrIII by 52 affords pyridinium ion 53, the subsequent deprotonation of which by the phosphate anion completes the catalytic cycle. Enantioselective reductive cross‐coupling of nitrones with aldehydes; Sc(OTf)3=scandium(III) trifluoromethanesulfonate, TEEDA=tetramethylethylenediamine, DCE=1,2‐dichloroethane. 2‐Acylimidazole or 2‐acylpyridine 155 first coordinates with the Rh catalyst, Δ‐RhS2, which then goes through base‐induced deprotonation to produce Rh enolate 159. N‐Arylamines coupled with aldehydes, ketones, and imines by means of photocatalytic proton‐coupled electron transfer. However, the use of a reductant in a stoichiometric quantity poses a substantial challenge for enantioselective induction from chiral ligands. Copyright © 1988 Published by Elsevier B.V. Journal of Photochemistry and Photobiology A: Chemistry, https://doi.org/10.1016/1010-6030(88)85002-0. In all cases the Ref. The scope of the reaction is broad, and even alkyl imines can be successfully reduced into the corresponding α‐amino radicals. of the whole article in a thesis or dissertation. From the combined reactivity and spectroscopic evidence, we propose that the ability of a catalyst to produce and stabilize the ketyl radical intermediate is a key descriptor in its ability to mediate the C–C coupling chemistry of aldehydes and ketones. The ketyl molecule is intensely colored. iScience. (A) Current synthetic approaches to ketyl radicals rely on strong reductants that reduce both the carbonyl and subsequent radical intermediates. Li SS, Zhu N, Jing YN, Li Y, Bao H, Wan WM. Descărcaţi. O‐H hydrogen bonding promotes H‐atom transfer from α‐C−H bonds for C alkylation of alcohols. reported a visible‐light‐activated asymmetric process involving a Rh catalyst acting as both a photocatalyst and a Lewis acid catalyst. In addition, stoichiometric quantities of the reductant lead to unavoidable side reactions such as reduction of the substrates.16 Moreover, limited substrates and high costs have also pushed chemists to find more efficient reactions for the generation of ketyl radicals. Reactions that involve the concerted shift of a single electron and a single proton are often called proton‐coupled electron‐transfer (PCET) reactions.27 The umpolung reactions of carbonyl compounds that exploit PCET often utilize an acid activator to lower the energy barrier during the SET process, as this facilitates the formation of ketyl radical intermediates.28. Both 88 and 89 are able to engage in PCET with substrate 85 to produce ketyl radical 87. Finally, 119 and 120 rapidly couple through a radical coupling reaction to afford target reduction product 116 after elimination of a cyanide anion. and RuI(bpy)3+. Silylated ketyl radical 18 subsequently couples with α‐aminomethyl radical 15 to afford rhodium‐bound silylated product 19. Spectroscopic features of the ketyl radical are observed on Au and Cu surfaces at benzaldehyde reduction potentials, but not on Pd and Pt. Moreover, a wide range of functionalized alcohols such as amino alcohols, benzyl alcohols, cyclitols, pinacols, and lactones, which are impossible to produce with traditional reaction procedures, can be easily obtained through mild and efficient photocatalytic transformations. Fava E, Millet A, Nakajima M, Loescher S, Rueping M. Angew Chem Int Ed Engl. With the inclusion of acetic acid, the reduction potential of aryl ketone 60 is dramatically elevated.

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