Single-Electron Oxidation-Induced Chemical Transformations: Carbon-Carbon Bond Formation and Selective Oxaziridine Rearrangement

Shafrizal Rasyid Atriardi, and Sang Kook Woo*

Department of Chemistry University of Ulsan, 93 Daehak-Ro Nam-gu, Ulsan 44610, Republic of Korea

woosk@ulsan.ac.kr

Abstract

Visible-light photoredox catalysis is an important and growing research area in the field of green and sustainable organic synthesis. One of the main mechanisms involved in photoredox catalysis is single-electron transfer (SET), which has been extensively investigated in our group for the development of greener carbon–carbon bond forming reactions and oxaziridine rearrangement. In this review, we highlight our results on the development and application of neutral silicon radical precursors for the generation of alkyl radicals and the selective rearrangement of oxaziridines into nitrones or amides.

1. Introduction

In the past decade, visible-light photoredox catalysis has received significant attention in the field of sustainable organic synthesis because of its inexpensive, abundant, and clean light sources and mild reaction conditions, which have led to the development of many organic reactions that are facilitated by visible-light photocatalysts.¹ Single-electron transfer (SET), in which radical species are produced, is one of the main mechanisms by which photoredox catalysis takes place. The SET mechanism can be classified into oxidative and reductive quenching cycles according to the redox state of the catalyst in the catalytic cycle (Figure 1, Part (a)).^1b,f,2 The spontaneity of the SET mechanism can be easily predicted from the Gibbs energy of a photoinduced electron transfer (ΔG_PET = −F[E_red(A/A^•−) − E_ox(D^•+/D)] − w − ΔE_0,0), where the redox potentials of catalysts and substrates can be obtained from the literature or determined through cyclic voltammetry. Our research has focused on the use of SET in photoredox catalysis for carbon–carbon bond forming reactions and oxaziridine rearrangement using transition-metal-based and organic photocatalysts such as Ru(bpz)₃(PF₆)₂, Ir(dF(CF₃)ppy)₂(dtbpy)PF₆, Fukuzumi’s acridinium salt (Acr⁺–Mes), 2,4,5,6-tetrakis(9H-carbazol-9-yl)-isophthalonitrile (4CzIPN), and 2,4,5,6-tetrakis(3,6-dichloro-9H-carbazol-9-yl)isophthalonitrile (Cl-4CzIPN), which are good oxidizers (Figure 1, Part (b)). In particular, we have favored organic photocatalysts because of their low cost and easy preparation. In this review, we present the results of our investigations of neutral silicon-based radical precursors for the generation of alkyl radicals via SET and the selective rearrangement of oxaziridines into nitrones or amides.

Figure 1. (a) Single-Electron Transfer (SET) Mechanism. (b) Popular Oxidizer Photocatalysts. (Ref. 1)

2. Development and Application of Neutral Silicon-Based Radical Precursors

2.1. Photoredox-Catalyzed Giese Reaction

2.2. Radical–Polar Crossover (RPC) Reaction for the Synthesis of gem-Difluoroalkenes

2.3. Imine Addition and Sequential One-Pot Deprotection of para-Methoxyphenyl (PMP) Ether

 

3. Selective Rearrangement of Oxaziridines into Nitrones and Amides

 

4. Conclusion

In this review, we have summarized our contributions to the development of greener and more sustainable reactions proceeding via a SET mechanism in photoredox catalysis for the formation of carbon–carbon bonds and the rearrangement of oxaziridines. We have developed neutral, silicon-based precursors of alkoxymethyl, hydroxymethyl, and allylic radicals and used them in Giese reactions, RPC reactions, and imine addition reactions to form new carbon–carbon bonds. These reactions provide access to a wide range of valuable scaffolds such as ethers, alcohols, 2,3-dihydrofurans, α-cyano-γ-butyrolactones, γ-butyrolactones, allylic compounds, gem-difluoroalkenes, β-amino ethers, and β-amino alcohols. We have also demonstrated the selective rearrangement of oxaziridines into nitrones and amides under photocatalytic conditions. The rearrangement of oxaziridines to nitrones was selectively observed in acetonitrile, ethyl acetate, and acetone as solvents, while amides were formed through a weak-base–promoted rearrangement that utilizes weak bases such as CF₃CO₂⁻ and DMF. Our ongoing research efforts aim to further improve silicon-based alkyl radical precursors for the generation and utilization of various alkyl radicals and to further explore the chemical conversion of oxaziridines. It is our sincere hope that our research will contribute to the expansion of ecologically friendly organic synthesis.

 5. Acknowledgments

This work was supported by a National Research Foundation of Korea (NRF) grant funded by the Korean government (MSIT) (NRF-2022R1A2C1005108 and 2021R1A4A1027480).

Trademarks. Amberlite^® (TDDP Specialty Electronic Materials US 8, LLC).

References

1. (a) Narayanam JMR, Stephenson CRJ. 2011. Visible light photoredox catalysis: applications in organic synthesis. Chem. Soc. Rev. 40(1):102-113. https://doi.org/10.1039/B913880N (b) Tucker JW, Stephenson CRJ. 2012. Shining Light on Photoredox Catalysis: Theory and Synthetic Applications. J. Org. Chem. 77(4):1617-1622. https://doi.org/10.1021/jo202538x (c) Xuan J, Xiao WJ. 2012. Visible-Light Photoredox Catalysis. Angew. Chem., Int. Ed. 51(28):6828-6838. https://doi.org/10.1002/anie.201200223 (d) Prier CK, Rankic DA. MacMillan DWC. 2013. Visible light photoredox catalysis with transition metal complexes: applications in organic synthesis. Chem. Rev. 113(7):5322-5363. https://doi.org/10.1021/cr300503r (e) Fukuzumi S, Ohkubo K. 2014. Organic synthetic transformations using organic dyes as photoredox catalysts. Org. Biomol. Chem. 12(32):6059-6071. https://doi.org/10.1039/c4ob00843j (f) Romero NA, Nicewicz DA. 2016. Organic Photoredox Catalysis. Chem. Rev. 116(17):10075-10166. https://doi.org/10.1021/acs.chemrev.6b00057 (g) Shaw MH, Twilton J, MacMillan DWC. 2016. Photoredox Catalysis in Organic Chemistry. J. Org. Chem. 81(16):6898-6926. https://doi.org/10.1021/acs.joc.6b01449 (h) Shang TY, Lu LH, Cao Z, Liu Y, He WM, Yu B. 2019. Recent advances of 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) in photocatalytic transformations. Chem. Commun. 55(38):5408-5419. https://doi.org/10.1039/c9cc01047e (i) Crespi S, Fagnoni M. 2020. Generation of Alkyl Radicals: From the Tyranny of Tin to the Photon Democracy. Chem. Rev. 120(17):9790-9833. https://doi.org/10.1021/acs.chemrev.0c00278 (j) Gontala A, Jang GS, Woo SK. 2021. Visible‐Light Photoredox‐Catalyzed α‐Allylation of α‐Bromocarbonyl Compounds Using Allyltrimethylsilane. Bull. Korean Chem. Soc. 42(3):506-509. https://doi.org/10.1002/bkcs.12219

2. Rehm D, Weller A. 1970. Kinetics of Fluorescence Quenching by Electron and H-Atom Transfer. Isr. J. Chem. 8(2):259-271. https://doi.org/10.1002/ijch.197000029

3. Yasu Y, Koike T, Akita M. 2012. Visible Light-Induced Selective Generation of Radicals from Organoborates by Photoredox Catalysis. Adv. Synth. Catal. 354(18):3414-3420. https://doi.org/10.1002/adsc.201200588

4. Kitcatt DM, Nicolle S, Lee A. 2022. Direct decarboxylative Giese reactions. Chem. Soc. Rev. 51(4):1415-1453. https://doi.org/10.1039/d1cs01168e

5. Corcé V, Chamoreau L, Derat E, Goddard J, Ollivier C, Fensterbank L. 2015. Silicates as Latent Alkyl Radical Precursors: Visible‐Light Photocatalytic Oxidation of Hypervalent Bis‐Catecholato Silicon Compounds. Angew Chem Int Ed. 54(39):11414-11418. https://doi.org/10.1002/anie.201504963

6. Gutiérrez-Bonet Á, Tellis JC, Matsui JK, Vara BA, Molander GA. 2016. 1,4-Dihydropyridines as Alkyl Radical Precursors: Introducing the Aldehyde Feedstock to Nickel/Photoredox Dual Catalysis. ACS Catal. 6(12):8004-8008. https://doi.org/10.1021/acscatal.6b02786

7. He F, Ye S, Wu J. 2019. Recent Advances in Pyridinium Salts as Radical Reservoirs in Organic Synthesis. ACS Catal. 9(10):8943-8960. https://doi.org/10.1021/acscatal.9b03084

8. Murarka S. 2018. N‐(Acyloxy)phthalimides as Redox‐Active Esters in Cross‐Coupling Reactions. Adv Synth Catal. 360(9):1735-1753. https://doi.org/10.1002/adsc.201701615

9. Yoshida J, Maekawa T, Murata T, Matsunaga S, Isoe S. 1990. Electrochemical oxidation of organosilicon compounds. Part 7. The origin of .beta.-silicon effect in electron-transfer reactions of silicon-substituted heteroatom compounds. Electrochemical and theoretical studies. J. Am. Chem. Soc. 112(5):1962-1970. https://doi.org/10.1021/ja00161a049

10. Gant Kanegusuku AL, Roizen JL. 2021. Recent Advances in Photoredox‐Mediated Radical Conjugate Addition Reactions: An Expanding Toolkit for the Giese Reaction. Angew Chem Int Ed. 60(39):21116-21149. https://doi.org/10.1002/anie.202016666

11. De Vleeschouwer F, Van Speybroeck V, Waroquier M, Geerlings P, De Proft F. 2007. Electrophilicity and Nucleophilicity Index for Radicals. Org. Lett. 9(14):2721-2724. https://doi.org/10.1021/ol071038k

12. (a) Nakata T. 2005. Total Synthesis of Marine Polycyclic Ethers. Chem. Rev. 105(12):4314-4347. https://doi.org/10.1021/cr040627q (b) Doherty EM, Fotsch C, Bannon AW, Bo Y, Chen N,  Dominguez C, Falsey J, Gavva NR, Katon J, Nixey T, et al. 2007. Novel Vanilloid Receptor-1 Antagonists:  2. Structure−Activity Relationships of 4-Oxopyrimidines Leading to the Selection of a Clinical Candidate. J. Med. Chem. 50(15):3515–3527. https://doi.org/10.1021/jm070190p

13.

(a) Lund T, Wayner DDM, Jonsson M, Larsen AG,  Daasbjerg K. 2001. Oxidation Potentials of α-Hydroxyalkyl Radicals in Acetonitrile Obtained by Photomodulated Voltammetry. J. Am. Chem. Soc. 123(50):12590-12595. https://doi.org/10.1021/ja011217b (b) Jin J, MacMillan DWC. 2015. Direct α-Arylation of Ethers through the Combination of Photoredox-Mediated C-H Functionalization and the Minisci Reaction. Angew. Chem., Int. Ed. 127(5):1585-1589. https://doi.org/10.1002/anie.201410432

14.

Khatun N, Kim MJ, Woo SK. 2018. Visible-Light Photoredox-Catalyzed Hydroalkoxymethylation of Activated Alkenes Using α-Silyl Ethers as Alkoxymethyl Radical Equivalents. Org. Lett. 20(19):6239-6243. https://doi.org/10.1021/acs.orglett.8b02721

15.

Liu W, Khedkar V, Baskar B, Schürmann M, Kumar K. 2011. Branching Cascades: A Concise Synthetic Strategy Targeting Diverse and Complex Molecular Frameworks. Angew. Chem. Int. Ed. 50(30):6900-6905. https://doi.org/10.1002/anie.201102440

16.

Nam SB, Khatun N, Kang YW, Park BY, Woo SK. 2020. Controllable one-pot synthesis for scaffold diversity via visible-light photoredox-catalyzed Giese reaction and further transformation. Chem. Commun. 56(19):2873-2876. https://doi.org/10.1039/c9cc08781h

17.

(a) Wang Y,  Zheng Z, Liu S, Zhang H, Li E, Guo L, Che Y. 2010. Oxepinochromenones, Furochromenone, and their Putative Precursors from the Endolichenic Fungus Coniochaeta sp. J. Nat. Prod. 73(5):920-924. https://doi.org/10.1021/np100071z (b) Rossi D, Nasti R, Collina S, Mazzeo G, Ghidinelli S,  Longhi G, Memo M, Abbate S. 2017. The role of chirality in a set of key intermediates of pharmaceutical interest, 3-aryl-substituted-γ-butyrolactones, evidenced by chiral HPLC separation and by chiroptical spectroscopies. J. Pharm. Biomed. Anal. 144:41-51. https://doi.org/10.1016/j.jpba.2017.01.007

18.

(a) Yamamoto Y, Nishii S, Maruyama K. 1985. The threo-selective reaction of but-2-enyl organometallic compounds with ethylidenemalonates and related compounds. J. Chem. Soc., Chem. Commun. (7):386-388. https://doi.org/10.1039/C39850000386 (b) Yamamoto Y, Nishii S. 1988. The anti-selective Michael addition of allylic organometals to ethylidenemalonates and related compounds. J. Org. Chem. 53(15):3597-3603. https://doi.org/10.1021/jo00250a034 (c) Araki S, Horie T, Kato M, Hirashita T, Yamamura H, Kawai M. 1999. Regioselective allylation and alkylation of electron-deficient alkenes with organogallium and organoindium reagents. Tetrahedron Lett. 40(12):2331-2334. https://doi.org/10.1016/S0040-4039(99)00179-3 (d) Shibata I, Kano T, Kanazawa N, Fukuoka S, Baba A. 2002. Generation of Organotantalum Reagents and Conjugate Addition to Enones. Angew. Chem., Int. Ed. 114(8):1447-1450. https://doi.org/10.1002/1521-3773(20020415)41:8<1389::AID-ANIE1389>3.0.CO;2-D

19.

(a) Mizuno K, Ikeda M, Otsuji Y. 1988. Dual Regioselectivity in the Photoallylation of Electron-Deficient Alkenes by Allylic Silanes. Chem. Lett. 17(9):1507-1510. https://doi.org/10.1246/cl.1988.1507 (b) Mizuno K, Hayamizu T, Maeda H. 2003. Regio- and stereoselective functionalization of electron-deficient alkenes by organosilicon compounds via photoinduced electron transfer. Pure Appl. Chem. 75(8):1049-1054. https://doi.org/10.1351/pac200375081049

20.

Gontala A, Woo SK. 2020. Visible‐Light Photoredox‐Catalyzed α‐Regioselective Conjugate Addition of Allyl Groups to Activated Alkenes. Adv Synth Catal. 362(15):3223-3228. https://doi.org/10.1002/adsc.202000445

21.

Hoyte RM, Denney DB. 1974. Cis-trans isomerization of allylic radicals. J. Org. Chem. 39(17):2607-2612. https://doi.org/10.1021/jo00931a035

22.

(a) Pitzer L, Schwarz J L, Glorius F. 2019. Reductive radical-polar crossover: traditional electrophiles in modern radical reactions. Chem. Sci. 10(36):8285-8291. https://doi.org/10.1039/c9sc03359a (b) Wiles RJ, Molander GA. 2020. Photoredox-Mediated Net-Neutral Radical/Polar Crossover Reactions. Isr. J. Chem. 60(3-4):281-293. https://doi.org/10.1002/ijch.201900166

23.

(a) Hagmann WK. 2008. The Many Roles for Fluorine in Medicinal Chemistry. J. Med. Chem. 51(15):4359-4369. https://doi.org/10.1021/jm800219f (b) Purser S, Moore PR, Swallow S, Gouverneur V. 2008. Fluorine in medicinal chemistry. Chem. Soc. Rev. 37(2):320-330. https://doi.org/10.1039/ b610213c (c) Gillis EP, Eastman KJ, Hill MD, Donnelly DJ, Meanwell NA. 2015. Applications of Fluorine in Medicinal Chemistry. J. Med. Chem. 58(21):8315-8359. https://doi.org/10.1021/acs.jmedchem.5b00258 (d) Oh K, Chi DY. 2021. Direct Fluorination Strategy for the Synthesis of Fluorine-18 Labeled Oligopeptide—[¹⁸F]ApoPep-7. Bull. Korean Chem. Soc. 42(8):1161-1166. https://doi.org/10.1002/bkcs.12350

24.

Atriardi SR, Kim J, Anita Y, Woo SK. 2023. Synthesis of gem‐difluoroalkenes via photoredox‐catalyzed defluoroaryloxymethylation of α‐trifluoromethyl alkenes. Bull. Korean Chem. Soc. 44(1):50-54. https://doi.org/10.1002/bkcs.12633

25.

(a) Ager DJ, Prakash I, Schaad DR. 1996. 1,2-Amino Alcohols and Their Heterocyclic Derivatives as Chiral Auxiliaries in Asymmetric Synthesis. Chem. Rev. 96(2):835-876. https://doi.org/10.1021/cr9500038 (b) Bergmeier SC. 2000. The Synthesis of Vicinal Amino Alcohols. Tetrahedron. 56(17):2561-2576. https://doi.org/10.1016/S0040-4020(00)00149-6

26.

Ahn DK, Kang YW, Woo SK. 2019. Oxidative Deprotection ofp-Methoxybenzyl Ethers via Metal-Free Photoredox Catalysis. J. Org. Chem. 84(6):3612-3623. https://doi.org/10.1021/acs.joc.8b02951

27.

Gontala A, Huh H, Woo SK. 2023. Photoredox-Catalyzed Synthesis of β-Amino Alcohols: Hydroxymethylation of Imines with α-Silyl Ether as Hydroxymethyl Radical Precursor. Org. Lett. 25(1):21-26. https://doi.org/10.1021/acs.orglett.2c03633

28.

(a) Hayyan M, Hashim MA, AlNashef IM. 2016. Superoxide Ion: Generation and Chemical Implications. Chem. Rev. 116(5):3029-3085. https://doi.org/10.1021/acs.chemrev.5b00407 (b) Tay NES, Nicewicz DA. 2017. Cation Radical Accelerated Nucleophilic Aromatic Substitution via Organic Photoredox Catalysis. J. Am. Chem. Soc. 139(45):16100-16104. https://doi.org/10.1021/jacs.7b10076

29.

(a) Williamson KS, Michaelis DJ, Yoon TP. 2014. Advances in the Chemistry of Oxaziridines. Chem. Rev. 114(16):8016-8036. https://doi.org/10.1021/cr400611n (b) Davis FA. 2018. Recent applications of N-sulfonyloxaziridines (Davis oxaziridines) in organic synthesis. Tetrahedron. 74(26):3198-3214. https://doi.org/10.1016/j.tet.2018.02.029 (c) Woo SK. 2022. Oxaziridines and Oxazirines. In Comprehensive Heterocyclic Chemistry IV, Vol. 1, 582–611. https://doi.org/10.1016/B978-0-12-409547-2.14812-7

30.

(a) Ohba Y, Kubo K, Sakurai T. 1998. Sensitized ring-opening reactions of 3-(1-naphthyl)-2-(1-naphthalenemethyl) oxaziridine. J. Photochemistry and Photobiology A:  Chemistry. 113(1):45-51. https://doi.org/10.1016/S1010-6030(97)00313-4 (b) Iwano Y, Kawamura Y, Horie T. 1995. Stereoselective Ring Opening of Geometrically Constrained Oxaziridines by Photosensitized Electron Transfer. Chem. Lett. 24:67-68. https://doi.org/10.1246/cl.1995.67 (c) Iwano Y, Kawamura Y, Miyoshi H, Yoshinari T, Horie T. 1994. Photosensitized Electron-Transfer Reaction of 3-Aryl-2-methyloxaziridine: Direct Deoxygenation from the Isomeric Arylnitrone. Bull. Chem. Soc. Jpn. 67(8):2348-2350. https://doi.org/10.1246/bcsj.67.2348

31.

(a) Gothelf KV, Jørgensen KA. 1998. Asymmetric 1,3-Dipolar Cycloaddition Reactions. Chem. Rev. 98(2):863-910. https://doi.org/10.1021/cr970324e (b) Stanley LM, Sibi MP. 2008. Enantioselective Copper-Catalyzed 1,3-Dipolar Cycloadditions. Chem. Rev. 108(8):2887-2902. https://doi.org/10.1021/cr078371m (c) Hashimoto T, Maruoka K. 2015. Recent Advances of Catalytic Asymmetric 1,3-Dipolar Cycloadditions. Chem. Rev. 115(11), 5366-5412. https://doi.org/10.1021/cr5007182

32.

Jang GS, Lee J, Seo J, Woo SK. 2017. Synthesis of 4-Isoxazolines via Visible-Light Photoredox-Catalyzed [3 + 2] Cycloaddition of Oxaziridines with Alkynes. Org. Lett. 19(23):6448-6451. https://doi.org/10.1021/acs.orglett.7b03369

33.

Oliveros E, Riviere M, Malrieu JP, Teichteil C. 1979. Theoretical exploration of the photochemical rearrangement of oxaziridines. J. Am. Chem. Soc. 101(2):318-322. https://doi.org/10.1021/ja00496a007

34.

Newcomb M, Reeder RA. 1980. Reactions of trans-2-tert-butyl-3-phenyloxaziridine with lithium amide bases. J. Org. Chem. 45(8):1489-1493. https://doi.org/10.1021/jo01296a029

35.

Park J, Park S, Jang GS, Kim RH, Jung J, Woo SK. 2021. Weak base-promoted selective rearrangement of oxaziridines to amides via visible-light photoredox catalysis. Chem. Commun. 57(78):9995-9998. https://doi.org/10.1039/d1cc03855a