Abstract
In this review, the journey of free radicals, from being shrewdly untamable until its emergence as a powerful tool in chemistry, has been tracked. A modern perspective on the generation of radicals has been offered through the lens of photoredox, metal mediation, redox-active scaffolds, and EDA complexes. Spotlight has been on the catalysis of radical reactions harboring unique strategies like smart initiation, electron and hole catalysis, and polarity reversal catalysis.
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(a) Romero K J, Galliher M S, Pratt D A and Stephenson C R 2018 Radicals in natural product synthesis Chem. Soc. Rev. 47 785; (b) Plesniak M P, Huang H-M and Procter D J 2017 Radical Cascade Reactions Triggered by Single Electron Transfer Nat. Rev. Chem. 1 0077; (c) Motherwell W B and Crich D 2013 Free Radical Chain Reactions in Organic Synthesis (London: Elsevier); (d) Gibian M and Corley R C 1973 Organic Radical-Radical Reactions. Disproportionation vs. Combination Chem. Rev. 73 441; (e) Curran D P 1988 The design and application of free radical chain reactions in organic synthesis. Part 1 Synthesis 6 417; (f) Gao Y, Zhou D, Lyu J, Sigen A, Xu Q, Newland B, Matyjaszewski K, Tai H and Wang W 2020 Complex Polymer Architectures through Free-Radical Polymerization of Multivinyl Monomers Nat. Rev. Chem. 4 194; (g) Studer A and Curran D P 2016 Catalysis of Radical Reactions: A Radical Chemistry Perspective Angew. Chem. Int. Ed. 55 58
Hedstrand D M, Kruizinga W H and Kellogg R M 1978 Light Induced and Dye Accelerated Reductions of Phenacyl Onium Salts by 1,4-Dihydropyridines Tetrahedron Lett. 19 1255
Pandey G, Ghorai M K and Hajra S 1996 Design of a Photosystem to Harvest Visible-Light into Electrons: Photosensitised One Electron Redox Reactions in Organic Synthesis Pure Appl. Chem. 68 653
Ischay M A, Anzovino M E, Du J and Yoon T P 2008 Efficient Visible Light Photocatalysis of [2+2] Enone Cycloadditions J. Am. Chem. Soc. 130 12886
Nicewicz D A and MacMillan D W C 2008 Merging Photoredox Catalysis with Organocatalysis: The Direct Asymmetric Alkylation of Aldehydes Science 322 77
Lu Z and Yoon T P 2012 Visible Light Photocatalysis of [2+2] Styrene Cycloadditions by Energy Transfer Angew. Chem. - Int. Ed. 51 10329
Tucker J W, Zhang Y, Jamison T F and Stephenson C R J 2012 Visible-Light Photoredox Catalysis in Flow Angew. Chem. 124 4220
Iqbal J, Bhatia B and Nayyar N K 1994 Transition Metal-Promoted Free-Radical Reactions in Organic Synthesis: The Formation of Carbon-Carbon Bonds Chem. Rev. 94 519
Nugent W A and RajanBabu T V 1988 Transition-Metal-Centered Radicals in Organic Synthesis. Titanium(III)-Induced Cyclization of Epoxyolefins J. Am. Chem. Soc. 110 8561
Basch C H, Liao J, Xu J, Piane J J and Watson M P 2017 Harnessing Alkyl Amines as Electrophiles for Nickel-Catalyzed Cross Couplings via C-N Bond Activation J. Am. Chem. Soc. 139 5313
(a) Crisenza G E, Mazzarella D and Melchiorre P 2020 Synthetic Methods Driven by the Photoactivity of Electron Donor–Acceptor Complexes J. Am. Chem. Soc. 142 5461; (b) Lima C G, de M Lima T, Duarte M, Jurberg I D and Paixao M W 2016 Organic synthesis enabled by light-irradiation of EDA complexes: theoretical background and synthetic applications ACS Catal. 6 1389; (c) Yuan Y Q, Majumder S, Yang M H and Guo S R 2020 Recent advances in catalyst-free photochemical reactions via electron-donor-acceptor (EDA) complex process Tetrahedron Lett. 61 151506; (d) Sun J, He Y, An X De, Zhang X, Yu L and Yu S 2018 Visible-Light-Induced Iminyl Radical Formation: Via Electron-Donor-Acceptor Complexes: A Photocatalyst-Free Approach to Phenanthridines and Quinolines Org. Chem. Front. 5 977
(a) Narayanam J M and Stephenson C R 2011 Visible light photoredox catalysis: applications in organic synthesis Chem. Soc. Rev. 40 102; (b) Majek M, Filace F and von Wangelin A J 2014 On the mechanism of photocatalytic reactions with eosin Y Beilstein J. Org. Chem. 10 981; (c) Cismesia M A and Yoon T P 2015 Characterizing chain processes in visible light photoredox catalysis Chem. Sci. 6 5426; (d) Kärkäs M D, Matsuura B S and Stephenson C R 2015 Enchained by visible light-mediated photoredox catalysis Science 349 1285; (e) Silvi M, Schrof R, Noble A and Aggarwal V K 2018 Enantiospecific Three-Component Alkylation of Furan and Indole Chem. - A Eur. J. 24 4279
Ho H E, Pagano A, Rossi-Ashton J A, Donald J R, Epton R G, Churchill J C, James M J, O’Brien P, Taylor R J K and Unsworth W P 2020 Visible-Light-Induced Intramolecular Charge Transfer in the Radical Spirocyclisation of Indole-Tethered Ynones Chem. Sci. 11 1353
Budén M E, Vaillard V A, Martin S E and Rossi R A 2009 Synthesis of Carbazoles by Intramolecular Arylation of Diarylamide Anions J. Org. Chem. 74 4490
Rossi R A, Alonso R A and Palacios S M 1981 Photostimulated Reactions of Potassium Diphenylarsenide with Haloarenes by the SRNl Mechanism J. Org. Chem. 46 2498
Camargo Solórzano P, Brigante F, Pierini A B and Jimenez L B 2018 Photoinduced Synthesis of Dibenzofurans: Intramolecular and Intermolecular Comparative Methodologies J. Org. Chem. 83 7867
Woods E F, Berl A J and Kalow J A 2020 Photocontrolled Synthesis of N-Type Conjugated Polymers Angew. Chemie - Int. Ed. 59 6062
Studer A and Curran D P 2014 The Electron is a Catalyst Nat. Chem. 6 765
Gu Z Y, Cao J J, Wang S Y and Ji S J 2016 The involvement of the trisulfur radical anion in electron-catalyzed sulfur insertion reactions: facile synthesis of benzothiazine derivatives under transition metal-free conditions Chem. Sci. 7 4067
Hokamp T, Dewanji A, Lübbesmeyer M, Mück‐Lichtenfeld C, Würthwein EU and Studer A 2017 Radical Hydrodehalogenation of Aryl Bromides and Chlorides with Sodium Hydride and 1, 4‐Dioxane Angew. Chem. Int. Ed. 56 13275
Tang X and Studer A 2018 Alkene 1, 2‐Difunctionalization by Radical Alkenyl Migration Angew. Chem. Int. Ed. 130 822
Okura K, Teranishi T, Yoshida Y and Shirakawa E 2018 Electron‐Catalyzed Cross‐Coupling of Arylboron Compounds with Aryl Iodides Angew. Chem. Int. Ed. 57 7186
Huang H M, McDouall J J and Procter D J 2019 SmI2-catalysed cyclization cascades by radical relay Nat. Catal. 2 211
Pabon R A, Bellville D J and Bauld N L 1983 Cation radical Diels-Alder reactions of electron-rich dienophiles J. Am. Chem. Soc. 105 5158
Pitzer L, Sandfort F, Strieth-Kalthoff F and Glorius F 2017 Intermolecular Radical Addition to Carbonyls Enabled by Visible Light Photoredox Initiated Hole Catalysislena J. Am. Chem. Soc. 139 13652
Jiang H and Studer A 2018 Amidyl Radicals by Oxidation of α-Amido-Oxy Acids: Transition-Metal-Free Amidofluorination of Unactivated Alkenes Angew. Chem. Int. Ed. 57 10707
Goulet-Hanssens A, Rietze C, Titov E, Abdullahu L, Grubert L, Saalfrank P and Hecht S 2018 Hole Catalysis as a General Mechanism for Efficient and Wavelength-Independent Z → E Azobenzene Isomerization Chem. 4 1740
Haque M B and Roberts B P 1996 Enantioselective radical-chain hydrosilylation of prochiral alkenes using optically active thiol catalysts Tetrahedron Lett. 37 9123
Zhou R, Goh Y Y, Liu H, Tao H, Li L and Wu J 2017 Visible-Light-Mediated Metal-Free Hydrosilylation of Alkenes through Selective Hydrogen Atom Transfer for Si−H Activation Angew. Chem. Int. Ed. 56 16621
Ren S C, Zhang F L, Qi J, Huang Y S, Xu A Q, Yan H Y and Wang Y F 2017 Radical Borylation/Cyclization Cascade of 1,6-Enynes for the Synthesis of Boron-Handled Hetero- and Carbocycles J. Am. Chem. Soc. 139 6050
Hell S M, Meyer C F, Misale A, Sap J B I, Christensen K E, Willis M C, Trabanco A A and Gouverneur V 2020 Hydrosulfonylation of Alkenes with Sulfonyl Chlorides under Visible Light Activation Angew. Chem. Int. Ed. 59 11620
Dimakos V, Su H Y, Garrett G E and Taylor M S 2019 Site-Selective and Stereoselective C-H Alkylations of Carbohydrates via Combined Diarylborinic Acid and Photoredox Catalysis J. Am. Chem. Soc. 141 5149
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VG thanks Ramanujan Fellowship (RJN-2018/085) for the financial support. The authors thank IIT Kharagpur for the infrastructure provided.
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Khamrai, A., Ganesh, V. How to train free radicals for organic synthesis? A modern approach. J Chem Sci 133, 5 (2021). https://doi.org/10.1007/s12039-020-01868-0
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DOI: https://doi.org/10.1007/s12039-020-01868-0