Organic Letters
Letter
Radicals from 2-S-Pyridyl Thioesters. Adv. Synth. Catal. 2017, 359,
3560−3565.
Functionalised Oximes: Emergent Precursors for Carbon-, Nitrogen-
and Oxygen-Centred Radicals. Molecules 2016, 21, 63−86.
(8) (a) Portela-Cubillo, F.; Surgenor, B. A.; Aitken, R. A.; Walton, J.
C. Thermal rearrangement of indolyl oxime esters to pyridoindoles. J.
Org. Chem. 2008, 73, 8124−8127. (b) Portela-Cubillo, F.; Scott, J. S.;
Walton, J. C. 2-(Aminoaryl)alkanone O-phenyl oximes: versatile
reagents for syntheses of quinazolines. J. Org. Chem. 2008, 73, 5558−
5565.
(3) (a) Zhang, M.; Xie, J.; Zhu, C. A general deoxygenation
approach for synthesis of ketones from aromatic carboxylic acids and
alkenes. Nat. Commun. 2018, 9, 3517−3526. (b) Stache, E. E.; Ertel,
A. B.; Rovis, T.; Doyle, A. G. Generation of Phosphoranyl Radicals via
Photoredox Catalysis Enables Voltage−Independent Activation of
Strong C−O Bonds. ACS Catal. 2018, 8, 11134−11139.
(9) For selected transition metal catalytic reactions of oxime to
produce iminyl radical, see: (a) Ran, L.; Ren, Z.-H.; Wang, Y.-Y.;
Guan, Z.-H. Copper-catalyzed homocoupling of ketoxime carbox-
ylates for synthesis of symmetrical pyrroles. Green Chem. 2014, 16,
112−115. (b) Zhao, M. N.; Ren, Z. H.; Yu, L.; Wang, Y. Y.; Guan, Z.
H. Iron-Catalyzed Cyclization of Ketoxime Carboxylates and Tertiary
Anilines for the Synthesis of Pyridines. Org. Lett. 2016, 18, 1194−
1197. (c) Yang, L.; Gao, P.; Duan, X. H.; Gu, Y. R.; Guo, L. N. Direct
C-H Cyanoalkylation of Quinoxalin-2(1H)-ones via Radical C-C
Bond Cleavage. Org. Lett. 2018, 20, 1034−1037. (d) Zhao, J. F.;
Duan, X. H.; Gu, Y. R.; Gao, P.; Guo, L. N. Iron-Catalyzed
Decarboxylative Olefination of Cycloketone Oxime Esters with
alpha,beta-Unsaturated Carboxylic Acids via C-C Bond Cleavage.
Org. Lett. 2018, 20, 4614−4617. (e) Zhang, J. J.; Duan, X. H.; Wu, Y.;
Yang, J. C.; Guo, L. N. Transition-metal free C-C bond cleavage/
borylation of cycloketone oxime esters. Chem. Sci. 2019, 10, 161−166.
(10) For UV-induced homolysis of oxime, see: (a) Portela-Cubillo,
F.; Scanlan, E. M.; Scott, J. S.; Walton, J. C. From dioxime oxalates to
dihydropyrroles and phenanthridines via iminyl radicals. Chem.
Commun. 2008, 4189−4191. (b) McBurney, R. T.; Slawin, A. M.;
Smart, L. A.; Yu, Y.; Walton, J. C. UV promoted phenanthridine
syntheses from oxime carbonate derived iminyl radicals. Chem.
Commun. 2011, 47, 7974−7976. (c) McBurney, R. T.; Walton, J. C.
Dissociation or cyclization: options for a triad of radicals released
from oxime carbamates. J. Am. Chem. Soc. 2013, 135, 7349−7354.
(11) For the generation of iminyl radical from oxime via visible-light
catalysis, see: (a) Jiang, H.; An, X.; Tong, K.; Zheng, T.; Zhang, Y.;
Yu, S. Visible-light-promoted iminyl-radical formation from acyl
oximes: a unified approach to pyridines, quinolines, and phenan-
thridines. Angew. Chem., Int. Ed. 2015, 54, 4055−4059. (b) An, X. D.;
Yu, S. Visible-light-promoted and one-pot synthesis of phenanthri-
dines and quinolines from aldehydes and O-acyl hydroxylamine. Org.
Lett. 2015, 17, 2692−2695. (c) Davies, J.; Booth, S. G.; Essafi, S.;
Dryfe, R. A. W.; Leonori, D. Visible-Light-Mediated Generation of
Nitrogen-Centered Radicals: Metal-Free Hydroimination and Imino-
hydroxylation Cyclization Reactions. Angew. Chem., Int. Ed. 2015, 54,
14017−14021. (d) Shu, W.; Nevado, C. Visible-Light-Mediated
Remote Aliphatic C-H Functionalizations through a 1,5-Hydrogen
Transfer Cascade. Angew. Chem., Int. Ed. 2017, 56, 1881−1884.
(e) Li, J.; Zhang, P.; Jiang, M.; Yang, H.; Zhao, Y.; Fu, H. Visible
Light as a Sole Requirement for Intramolecular C(sp3)-H Imination.
Org. Lett. 2017, 19, 1994−1997.
(12) For the generation of C-radical from oxime via visible-light
catalysis, see: (a) Li, L.; Chen, H.; Mei, M.; Zhou, L. Visible-light
promoted gamma-cyanoalkyl radical generation: three-component
cyanopropylation/etherification of unactivated alkenes. Chem. Com-
mun. 2017, 53, 11544−11547. (b) Yu, X.-Y.; Chen, J.-R.; Wang, P.-Z.;
Yang, M.-N.; Liang, D.; Xiao, W.-J. A Visible-Light-Driven Iminyl
Radical-Mediated C−C Single Bond Cleavage/Radical Addition
Cascade of Oxime Esters. Angew. Chem., Int. Ed. 2018, 57, 738−
743. (c) Shen, X.; Zhao, J. J.; Yu, S. Photoredox-Catalyzed
Intermolecular Remote C-H and C-C Vinylation via Iminyl Radicals.
Org. Lett. 2018, 20, 5523−5527. (d) Dauncey, E. M.; Morcillo, S. P.;
Douglas, J. J.; Sheikh, N. S.; Leonori, D. Photoinduced Remote
Functionalisations by Iminyl Radical Promoted C-C and C-H Bond
Cleavage Cascades. Angew. Chem., Int. Ed. 2018, 57, 744−748.
(e) Wang, P. Z.; Yu, X. Y.; Li, C. Y.; He, B. Q.; Chen, J. R.; Xiao, W. J.
A photocatalytic iminyl radical-mediated C-C bond cleavage/
addition/cyclization cascade for the synthesis of 1,2,3,4-tetrahydro-
phenanthrenes. Chem. Commun. 2018, 54, 9925−9928. (f) Yu, X.-Y.;
Wang, P.-Z.; Yan, D.-M.; Lu, B.; Chen, J.-R.; Xiao, W.-J. Photo-
(4) (a) Norrish, R. G. W.; Bamford, C. H. Photodecomposition of
aldehydes and ketones. Nature 1936, 138, 1016. (b) Liu, J.; Liu, Q.;
Yi, H.; Qin, C.; Bai, R.; Qi, X.; Lan, Y.; Lei, A. Visible-light-mediated
decarboxylation/oxidative amidation of alpha-keto acids with amines
under mild reaction conditions using O2. Angew. Chem., Int. Ed. 2014,
53, 502−506. (c) Morack, T.; Muck-Lichtenfeld, C.; Gilmour, R.
Bioinspired Radical Stetter Reaction: Radical Umpolung Enabled by
Ion-Pair Photocatalysis. Angew. Chem., Int. Ed. 2019, 58, 1208−1212.
(d) Tan, H.; Li, H.; Ji, W.; Wang, L. Sunlight-Driven Decarboxylative
Alkynylation of alpha-Keto Acids with Bromoacetylenes by Hyper-
valent Iodine Reagent Catalysis: A Facile Approach to Ynones. Angew.
Chem., Int. Ed. 2015, 54, 8374−8377. (e) Wang, G. Z.; Shang, R.;
Cheng, W. M.; Fu, Y. Decarboxylative 1,4-Addition of alpha-
Oxocarboxylic Acids with Michael Acceptors Enabled by Photoredox
Catalysis. Org. Lett. 2015, 17, 4830−4833. (f) Cheng, W. M.; Shang,
R.; Yu, H. Z.; Fu, Y. Room-Temperature Decarboxylative Couplings
of alpha-Oxocarboxylates with Aryl Halides by Merging Photoredox
with Palladium Catalysis. Chem. - Eur. J. 2015, 21, 13191−13195.
(g) Huang, H.; Zhang, G.; Chen, Y. Dual Hypervalent Iodine(III)
Reagents and Photoredox Catalysis Enable Decarboxylative Ynony-
lation under Mild Conditions. Angew. Chem., Int. Ed. 2015, 54, 7872−
7876. (h) Jia, K.; Pan, Y.; Chen, Y. Selective Carbonyl-C(sp3) Bond
Cleavage To Construct Ynamides, Ynoates, and Ynones by Photo-
redox Catalysis. Angew. Chem., Int. Ed. 2017, 56, 2478−2481. (i) Goti,
G.; Bieszczad, B.; Vega-Penaloza, A.; Melchiorre, P. Stereocontrolled
Synthesis of 1,4-Dicarbonyl Compounds by Photochemical Organo-
catalytic Acyl Radical Addition to Enals. Angew. Chem., Int. Ed. 2019,
58, 1213−1217. (j) Zhou, Q. Q.; Guo, W.; Ding, W.; Wu, X.; Chen,
X.; Lu, L. Q.; Xiao, W. J. Decarboxylative alkynylation and
carbonylative alkynylation of carboxylic acids enabled by visible-
light photoredox catalysis. Angew. Chem., Int. Ed. 2015, 54, 11196−
11199.
(5) (a) Prier, C. K.; Rankic, D. A.; MacMillan, D. W. Visible light
photoredox catalysis with transition metal complexes: applications in
organic synthesis. Chem. Rev. 2013, 113, 5322−5363. (b) Beatty, J.
W.; Stephenson, C. R. Amine Functionalization via Oxidative
Photoredox Catalysis: Methodology Development and Complex
Molecule Synthesis. Acc. Chem. Res. 2015, 48, 1474−1484.
(c) Romero, N. A.; Nicewicz, D. A. Organic Photoredox Catalysis.
Chem. Rev. 2016, 116, 10075−10166. (d) Chen, J. R.; Hu, X. Q.; Lu,
L. Q.; Xiao, W. J. Visible light photoredox-controlled reactions of N-
radicals and radical ions. Chem. Soc. Rev. 2016, 45, 2044−2056.
(e) Chen, J. R.; Hu, X. Q.; Lu, L. Q.; Xiao, W. J. Exploration of
Visible-Light Photocatalysis in Heterocycle Synthesis and Function-
alization: Reaction Design and Beyond. Acc. Chem. Res. 2016, 49,
1911−1923. (f) Xuan, J.; Zhang, Z. G.; Xiao, W. J. Visible-Light-
Induced Decarboxylative Functionalization of Carboxylic Acids and
Their Derivatives. Angew. Chem., Int. Ed. 2015, 54, 15632−15641.
(6) Mohammed, A. H. A.; Nagendrappa, G. A remarkably simple α-
oximation of ketones to 1,2-dione monooximes using the chloro-
trimethylsilane−isoamyl nitrite combination. Tetrahedron Lett. 2003,
44, 2753−2755.
(7) (a) Walton, J. C. The oxime portmanteau motif: released
heteroradicals undergo incisive EPR interrogation and deliver diverse
heterocycles. Acc. Chem. Res. 2014, 47, 1406−1416. (b) Walton, J. C.
E
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