R35 GM119812/GM/NIGMS NIH HHS/United States. The reaction is initiated by visible‐light‐induced photoexcitation of IrIII[F(CF3)ppy]2(bpy)+ to its excited state, *IrIII[F(CF3)ppy]2(bpy)+. Single‐electron reduction of *IrIII(ppy)2(dtbbpy)+ by Hünig's base (iPr2NEt) produces the Hünig's base cation radical, which then undergoes the [1,2]‐H shift to generate ammonium radical 89. Presumably, secondary orbital interactions of the π orbital of the carbonyl group of the isatin lead to the generation of d,l‐isatide 167. O‐H hydrogen bonding promotes H‐atom transfer from α‐C−H bonds for C alkylation of alcohols. RuI(bpy)3+ is then oxidized by O2 through SET to regenerate the RuII(bpy)32+ photocatalyst, which closes the photocatalytic cycle. Then, the exciplex abstracts a hydrogen atom from isopropanol 148 to afford ketyl radical 151, and a mandelic acid radical is also generated that quickly dimerizes to give diphenyl tartaric acid (152). 1 Discovery of a redox-neutral ketyl radical coupling. Following this hypothesis, the Knowles group has developed an asymmetric intramolecular aza‐pinacol coupling reaction under synergistic catalysis conditions (Scheme 7).30 Chiral phosphoric acid (R,R)‐PA‐1 is supposed to be the asymmetric catalyst that merges the intramolecular radical‐coupling reaction to produce a wide range of cis‐amino alcohol products in high yields with excellent enantioselectivities. In the same year, he became a lecturer at the College of Science, Nanjing Agriculture University, China. Epub 2016 May 2. In 2013, Knowles and co‐workers developed a new photocatalytic protocol for an intramolecular ketyl–olefin coupling reaction by using the PCET concept (Scheme 6).29 The catalytic cycle is started with SET from Hantzsch ester (HEH) to photoexcited *RuII(bpy)32+ to release reduced RuI(bpy)3+ and the Hantzsch radical cation (HEH+.). reported a photocatalytic Barbier reaction to realize the synthesis of allylic and benzylic alcohols under photoredox reductive radical–radical cross‐coupling reaction conditions (Scheme 24).47 Different kinds of substituted aromatic aldehydes and ketones are transformed into the corresponding ketyl radicals and are then coupled with benzyl radicals or allyl radicals in moderate yields. In 2015, Rueping and co‐workers utilized the α‐ammonium radical as a hydrogen‐bond activator to induce the umpolung of carbonyl derivatives to produce the ketyl radical by a PCET process (Scheme 11).34 Different kinds of aldehydes, ketones, and aldimines can be readily dimerized under mild reaction conditions without additives. Finally, 1,2‐amino alcohol product 22 is generated by a protonation step. Synthetic Applications of Proton-Coupled Electron Transfer. See this image and copyright information in PMC. Synthetic scope of redox-neutral ketyl…. The reactivity of ketyl radical intermediates generated from carbonyls in the presence of in situ generated Brønsted acid activators was studied by the Pac group in 1983.33 In recent years (after 2015), however, much more elegant work has been reported, and the field has undergone rapid growth. Photoredox‐catalyzed coupling reaction between aldehydes/imines and 4‐vinylpyridine. (2015) degrees under the supervision of Prof. Hanhong Xu at South China Agriculture University.
Concerted PCET from IrII to ketone 55 activated by hydrogen bonding of the chiral phosphoric acid furnishes the ketyl radical, which binds to chiral phosphate 57. Ynamide Smiles Rearrangement Triggered by Visible-Light-Mediated Regioselective Ketyl-Ynamide Coupling: Rapid Access to Functionalized Indoles and Isoquinolines. However, a lack of mechanistic understanding hinders rational catalyst development for this coupling chemistry. In this work, the electrochemical reduction of benzaldehyde is employed as a model reaction to investigate the impact of four metals (Au, Cu, Pd and Pt) on the two carbonyl reduction pathways, i.e., direct electrochemical reduction to benzyl alcohol and reductive C–C coupling to a diol product, i.e., hydrobenzoin. Meaning of ketyl.
Reproduced material should be attributed as follows: If the material has been adapted instead of reproduced from the original RSC publication 4 0 obj<> endobj The reaction affords 1,2‐diamino alcohols 13 in high yields with excellent enantioselectivities.
Photoredox‐catalyzed intramolecular ketyl–olefin coupling reaction. In all cases the Ref. Moreover, the subsequent C−C bond‐coupling reaction between the ketyl radicals and C‐centered radicals or unsaturated bonds under photoredox conditions are also included, as they demonstrate the versatility and capacity for further applications. as radical anion by one-electron reduction of carbonyls with sodium. Moreover, ketone 48 is activated by the Brønsted acid catalyst (HX) through hydrogen bonding, and it then undergoes PCET to transfer an electron from RuI(bpy)3+ and a hydrogen atom from HX to the Brønsted acid–ketone complex. The benzophenone/sodium still is a widely used method to produce water, oxygen, and peroxide free solvents for organic synthesis1,2. demonstrated a visible‐light‐activated asymmetric process involving an Ir catalyst acting as both the photocatalyst and Lewis acid catalyst. Chemistry. The authors propose a catalytic cycle on the basis of experimental and computational studies; it is shown in Scheme 22. The most popular solvent for these reactions is tetrahydrofura…
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