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DOI: 10.1039/D5GC02386F (Communication) Green Chem., 2025, Advance Article

Photo-induced C(sp3)–H functionalization of unactivated alkanes under transition-metal- and photocatalyst-free conditions

Yonghong Liu† *abc, Wanqiang Wang†a, Wei Xub, Ting Panga, Ziren Chenb, Qi Xua, Xin Wangc, Yonghong Zhang*b and Ping Liu*a
aSchool of Chemistry and Chemical Engineering, Shihezi University, 832003, Shihezi, China. E-mail: yongh_liu@shzu.edu.cn; liuping1979112@aliyun.com
bState Key Laboratory of Chemistry and Utilization of Carbon Based Energy Resources, College of Chemistry, Xinjiang University, 830017, Urumqi, China. E-mail: zhzhzyh@126.com
cSchool of Chemistry, Dalian University of Technology, 116024, Dalian, China

Received 14th May 2025 , Accepted 3rd August 2025

First published on 6th August 2025

Abstract

The Giese reaction is a powerful method for C–C bond formation, but traditional approaches typically necessitate the incorporation of a leaving group on the substrate. Recent advancements combine photoredox catalysis and hydrogen atom transfer (HAT) to directly activate C(sp3)–H bonds, thereby bypassing the need for pre-functionalized substrates. However, the dependence on additional HAT reagents and expensive catalysts remains a critical challenge. Herein, we report a simple, metal-/photocatalyst-free photocatalytic system for the Giese-type reactions of unactivated alkanes by using only trace oxygen. This reaction involves the photo-excited benzylidenemalononitriles sensitizing triplet oxygen (3O2) to generate singlet oxygen (1O2), which subsequently oxidizes cycloalkanes and facilitates the Giese-type reaction under mild conditions.


Green foundation

1. Sustainability through a metal-/photocatalyst-free system: traditional Giese reactions often rely on expensive and potentially toxic catalysts. This study presents a metal- and photocatalyst-free system, which minimizes the use of rare and harmful materials, reducing the overall environmental impact. By eliminating the need for costly catalysts, the process becomes more sustainable, both economically and environmentally.

2. Utilizing trace oxygen for green activation: the reaction utilizes trace amounts of molecular oxygen (3O2) to generate singlet oxygen (1O2) for the activation of C–H bonds in cycloalkanes. Oxygen is a widely abundant, non-toxic, and renewable resource, making this method much more eco-friendly than conventional approaches that depend on hazardous reagents or complex systems for activation.

3. Mild conditions and reduced toxicity: the reaction is conducted under mild conditions, without the need for high temperatures or extreme pressures, which enhances energy efficiency and reduces the production of harmful by-products. Additionally, the use of singlet oxygen generated from environmentally benign oxygen avoids the toxicity concerns associated with many traditional hydrogen atom transfer reagents, offering a safer and greener alternative.


Introduction

The Giese reaction, as one of the most powerful and versatile strategies for C–C bond formation, has been widely employed in complex molecule synthesis and pharmaceutical modifications owing to its mild reaction conditions and outstanding functional group tolerance.1 Traditional reactions require substrates containing pre-installed leaving groups (such as halides) to enable in situ radical generation under heat, light, or radical initiator-mediated conditions in the presence of tin hydride (Scheme 1a).2 However, this strategy proves particularly challenging for the functionalization of unactivated alkanes due to the high C–H bond dissociation energies (BDEs, 90–100 kcal mol−1) of these inert alkanes,3 which in turn limits their widespread application in synthetic organic chemistry.
image file: d5gc02386f-s1.tif
Scheme 1 a) Traditional Giese reaction; (b) synergistically combining photoredox and HAT catalysis; (c) photoredox catalysis of activated C(sp3)–H bonds; and (d) this work. EWG = electron-withdrawing group.

The synergistic combination of photoredox catalysis and HAT has emerged as a sustainable and powerful strategy for the direct activation of inert C(sp3)–H bonds (Scheme 1b).4 Through the careful choice of suitable metal catalysts, photocatalysts, and HAT reagents, this approach enables the direct transformation of C(sp3)–H bonds into reactive C-centered radicals, thereby bypassing the necessity for pre-functionalized substrates.5 As a result, several research groups have established efficient methods for C(sp3)–H functionalization of unactivated alkanes under visible light irradiation in the presence of photocatalysts and optimized HAT reagents.6 One notable limitation is the reliance of these reactions on additional HAT reagents, which are commonly toxic, highlighting the importance of developing more environmentally benign catalytic approaches. The direct HAT reaction of photoexcited photocatalysts, instead of the traditional process relying on additional HAT reagents, offers a promising approach to address this issue. With this objective, the Wu,7 Ravelli,8 and Noël9 groups respectively reported light-induced eosin Y-, uranyl nitrate hexahydrate-, and TBADT-catalyzed direct HAT of inert alkanes, and successfully applied it to Giese-type addition reactions. Another strategy is the photo-induced ligand-to-metal charge transfer (LMCT) process.10 In this regard, groups such as those of Zuo,11 Schelter,12 Rovis,13 Jin,14 and Kanai15 have made significant contributions to the direct activation of C(sp3)–H bonds through photo-induced LMCT in Ce, Fe, Cu, and Ti halide complexes. However, the use of high-cost photocatalysts and the excessive reliance on metal catalysts in industrial production somewhat contradict the principles of green and sustainable development.

In recent years, photoredox-catalyzed single-electron oxidation and deprotonation of α-alkyl amines have provided a practical route to generate C-centered radicals.5b,16 The groups of Zhang,17 Rueping,18 and Jui19 have made similar contributions to this field (Scheme 1c). However, this catalytic system remains ineffective for unactivated C(sp3)–H bonds. As an extension of our radical-mediated organic reactions,20 we report here a simple and eco-friendly photo-induced catalytic system for the Giese-type reaction of unactivated alkanes in the presence of trace oxygen (Scheme 1d). In this protocol, we hypothesized that photoexcited benzylidenemalononitriles could sensitize 3O2 to form 1O2, which then drives the peroxidation of cycloalkanes. This is followed by homolytic cleavage and HAT to generate C-centered radicals. The reaction completes in a closed loop through radical addition and HAT, thereby bypassing the need for photocatalysts or metal catalysts.

Results and discussion

We began our studies by exploring the reaction between benzylidenemalononitrile 1a and cyclohexane 2a in a 1[thin space (1/6-em)]:[thin space (1/6-em)]10 equivalent ratio under irradiation of 2 × 30 W 390 nm LEDs in acetonitrile (MeCN), with tetrabutylammonium chloride (TBACl) as a phase-transfer additive. In this reaction, we assumed that the benzylidenemalononitrile substrates not only facilitated the sensitization of 3O2 to 1O2 through energy transfer but also effectively trapped the alkyl radical intermediates, thereby enabling the C(sp3)–H bond functionalization reaction of alkanes. The optimized reaction conditions are summarized in Table 1. After 40 h, we were pleased to observe that the desired C(sp3)–H functionalization reaction proceeded efficiently at room temperature, affording product 3a in an average 85% yield, while generating the reduction product 1a′ from 1a in an average 7% NMR yield (entry 1). The formation of 1a′ was likely due to the photoexcitation of 1a, which caused the cleavage of the π-bond followed by HAT. The influence of light sources on the reaction was first investigated. Irradiation with individual 30 W 390 nm LEDs instead of dual matched 390 nm LEDs decreased the yield of product 3a to 52% (entry 2), while utilizing a 40 W 370 nm Kessil lamp afforded the target product 3a in 47% NMR yield (entry 3). Shorter-wavelength UV irradiation afforded 3a in 58% yield but enhanced the formation of the reduction byproduct 1′ (entry 4). Next, other solvents were evaluated, revealing that the reaction proceeded smoothly in DCM but showed limited progress in DMF (entries 5 and 6). The oxygen concentration significantly influenced the reaction. Reducing the oxygen concentration below 0.5 ppm sharply decreased the target product yield, while a gradual increase to 5 ppm led to a rapid rise in yield (entries 7 and 8). Optimal performance was observed within the 6–10 ppm range, whereas exceeding this threshold resulted in a gradual decrease in product yield (entries 1 and 9). The open-to-air reaction significantly reduced the yield, affording the desired product 3a in merely 16% yield (entry 10). We presume that the high concentration of oxygen in the atmosphere will quench the cyclohexyl radical. It is worth mentioning that the reaction proceeded smoothly even in the absence of TBACl (entry 11). However, the reaction did not occur in the absence of light (entry 12).
Table 1 Reaction optimizationa

image file: d5gc02386f-u1.tif
Entry Variation from standard conditions 3a yieldb (%) 1a′ yieldb (%)
a All reactions were performed in 10 mL sealed tubes with 6–10 ppm O2, 1a (0.2 mmol, 1 equiv.), and 2a (10 equiv.).b Yields were determined by 1H NMR spectroscopy vs. an internal standard (1,3,5-trimethoxybenzene).c Isolated yield. ND = not detected. DCM = dichloromethane. DMF = N,N-dimethylformamide.
1 None 86 (85)c 7
2 30 W 390 nm LEDs (single) 52 5
3 40 W 370 nm Kessil lamp (single) 47 5
4 20 W 305–315 nm LEDs (single) 58 18
5 DCM instead of CH3CN 61 6
6 DMF instead of CH3CN Trace ND
7 O2 concentration: <0.5 ppm ∼27 ∼12
8 O2 concentration: 1 to 5 ppm 41 to 84 13 to 7
9 O2 concentration: 15 to 40 ppm 83 to 62 ∼7
10 Open to air conditions 16 ND
11 No TBACl 34 4
12 No light 0 0

Under the irradiation of dual matched 390 nm LEDs, the substrate scope for the photo-induced Giese-type addition reactions of alkanes to benzylidenemalononitriles in the presence of trace O2 was further investigated (Scheme 2). At the outset, various benzylidenemalononitriles 1 were explored, and cyclohexane 2a was selected as the coupling partner. Benzylidenemalononitriles with both electron-neutral (–H) and electron-donating (–Me) groups were accommodated perfectly (3a and 3b). Electron-withdrawing groups at the para-position of the phenyl were well tolerated, furnishing the desired products in excellent yields: 85% (–F, 3c), 85% (–Cl, 3d), 88% (–Br, 3e), 71% (–CN, 3f) and 74% (–OCF3, 3g). Groups such as –Br, –CF3, or –Cl at the meta- or ortho-position of the phenyl ring were also effective (3h–3k). In addition, the 2-naphthy group proved to be a suitable reaction partner and afforded 3l in 44% yield. Unfortunately, the introduction of a strong electron-donating group (e.g., –OMe) increased the yield of the byproduct 1′, and its polarity closely resembled that of the target product, making isolation difficult. Next, the scopes of cycloalkane and aliphatic cyclic ethers were also briefly evaluated. The results indicate that cyclopentane was a suitable substrate and gave the corresponding photocatalyzed alkylated product 3m in 78% yield. Moreover, aliphatic cyclic ethers including tetrahydropyran, 1,4-dioxane and tetrahydrothiophene afforded the desired products (3n–3q) in very good yields as mixtures of two diastereomers (dr = 1[thin space (1/6-em)]:[thin space (1/6-em)]1 or 1.4[thin space (1/6-em)]:[thin space (1/6-em)]1). Surprisingly, when toluene, mesitylene, ethylbenzene, and tetrahydronaphthalene were used as the aromatic substrates, the target product was still obtained with single regioselective products (3r–3v).


image file: d5gc02386f-s2.tif
Scheme 2 Substrate scope using benzylidenemalononitrile as the radical acceptor. Reactions were performed using 1 (0.2 mmol, 1.0 equiv.) and 2 (10 equiv.); all reactions were performed in 10 mL sealed tubes with 6–10 ppm O2, 2 × 30 W 390 nm LEDs, and CH3CN (0.1 M) for 40 h, isolated yield. a[thin space (1/6-em)]Diastereomeric ratios (dr) were determined by 1H NMR analysis. b[thin space (1/6-em)]3 equiv. of 2 was used; yields in parentheses were obtained without TBACl.

Boc-protected alkylhydrazine is a valuable chemical building block with substantial economic and practical potential.11a,14a,21 With the above success, we further examined the substrate scope of cycloalkanes and aliphatic ethers using di-tert-butyl azodicarboxylate (DBAD) as the radical acceptor (Scheme 3). The optimization of the reaction conditions for DBAD with alkanes is detailed in the SI (S3). To our delight, generally good yields were obtained when cyclohexane and cyclopentane were used (5a and 5b). Notably, heteroatom-containing substrates exhibited exceptional reactivity, and the corresponding products were obtained in excellent yields ranging from 88% to 98% (5c–5f). Surprisingly, when linear diethyl ether was employed as the radical donor, the single regioselective product 5g could still be obtained in 83% yield. Inspired by the excellent regioselectivity of these substrates, we further extended the substrate scope to inert linear and branched alkanes to investigate the reaction's regioselectivity. Pleasingly, n-pentane, n-hexane, and 2,3-dimethylbutane were well tolerated, affording a mixture of regioisomeric products 5h–5j in moderate yields. The regioisomeric ratios (rr) of the functionalization products were determined to be 4.9[thin space (1/6-em)]:[thin space (1/6-em)]1.8[thin space (1/6-em)]:[thin space (1/6-em)]1 (5h), 4.6[thin space (1/6-em)]:[thin space (1/6-em)]2.8[thin space (1/6-em)]:[thin space (1/6-em)]1 (5i), and 1.8[thin space (1/6-em)]:[thin space (1/6-em)]1 (5j). Even when adamantane or cyclohexane was used as the coupling substrate, the reaction still afforded products 5k and 5l with general regioselectivity.


image file: d5gc02386f-s3.tif
Scheme 3 Substrate scope using DBAD as the radical acceptor. Reactions were performed using 4 (0.2 mmol, 1.0 equiv.), 2 (10 equiv.), N2 atmosphere, 2 × 30 W 390 nm LEDs, and CH3CN (0.1 M) for 28 h, isolated yield. a[thin space (1/6-em)]Without TBACl. b[thin space (1/6-em)]16 h. c[thin space (1/6-em)]Regioisomeric ratios (rr) were determined by GC analysis.

To gain deeper mechanistic insight, we performed a series of control experiments to elucidate the reaction pathway. First, under the standard reaction conditions, TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl) was added as a radical scavenger to both reaction systems, and the formation of the target products 3a and 5a was totally inhibited, while the cyclohexane–TEMPO adduct 6 was detected by HRMS (high-resolution mass spectrometry), confirming the presence of transient cyclohexyl radicals in this reaction (Scheme 4a). To elucidate the mechanism of formation of the cyclohexyl radical, we hypothesized that peroxides might be involved in the reaction. Accordingly, we employed triphenylphosphine (PPh3) as a probe for peroxides, given its well-established reactivity with peroxides to form triphenylphosphine oxide (OPPh3).22 Indeed, we successfully detected the mass of OPPh3 7 by HRMS, confirming the generation of trace peroxides in the reaction (Scheme 4b). The formation of peroxides may result from the photoexcited 1a sensitizing 3O2 to form 1O2, which then drives the peroxidation of cyclohexane. Next, we conducted an electron paramagnetic resonance (EPR) experiment using 2,2,6,6-tetramethylpiperidine (TEMP) as the 1O2 trap, which was known to be specifically oxidized by 1O2 to form TEMPO.23 Initially, no EPR signal was detected for a solution of 1a and TEMP in the dark (Scheme 4c, black line). Surprisingly, upon light irradiation of the mixture, characteristic three-line EPR signals emerged (Scheme 4c, red line), identifying the formation of TEMPO. These results suggested the presence of singlet oxygen in the reaction. However, UV-Vis absorption spectrum analysis showed that compound 1a displayed minimal absorption at the employed reaction wavelength (Scheme 4d), which suggests that the reaction may proceed through a two-photon excitation (TPE) process. To verify this possibility, the TPE parallel kinetic effect was evaluated by using light intensities of 20 W (black) and 40 W (red) (Scheme 4e). The magnitude of the value given by k40 W/k20 W was 3.1 for this photo-induced C(sp3)–H functionalization. This value indicates that the TPE process occurs in this catalytic system. In addition, light on/off experiments revealed the possibility of short-lived radical chain processes, as evidenced by persistent product formation (3–4% yields) under dark conditions following initial photoactivation (Scheme 4f, see the SI S10 for details).


image file: d5gc02386f-s4.tif
Scheme 4 Mechanistic investigations. (a) Radical trapping experiment. (b) Peroxide trapping experiment. (c) Electron paramagnetic resonance study. (d) UV-Vis absorption spectrum of 1a and DBAD. (e) Two-photon excitation kinetic effect experiments. (f) Light on/off experiments under Kessil lamp irradiation.

Based on these results, a reasonable reaction mechanism was proposed, as shown in Scheme 5. First, benzylidenemalononitrile 1a is excited to form 1a* via TPE under irradiation, which subsequently serves as the photosensitizer to transform ground-state 3O2 into reactive 1O2 through energy transfer. Next, peroxide A is generated via 1O2-mediated oxidation of cyclohexane 2a,24 followed by homolytic cleavage to afford the reactive oxygen radical species B. A subsequent HAT process between the oxygen radical and the C(sp3)–H bond of 2a generates the key cyclohexyl radical, and oxide C is clearly detectable by HRMS. The cyclohexyl radical is trapped by 1a to form the new radical intermediate D. Finally, product 3a is afforded through HAT between intermediate D and substrate 2a, with the regenerated cyclohexyl radical continuing to participate in the next radical additions with 1a. Alternatively, the excited-state 1a* may turn into the radical intermediate E and participate in HAT with cyclohexane to deliver the by-product 1a′.


image file: d5gc02386f-s5.tif
Scheme 5 Proposed catalytic mechanism.

Conclusions

In summary, we have developed an environmentally-friendly and reliable protocol for Giese-type reactions of unactivated alkanes and aliphatic ethers by utilizing trace O2 as a green oxidant under transition-metal- and photocatalyst-free conditions. The present approach proceeds at room temperature under light irradiation and employs benzylidenemalononitriles as both photosensitizers for 1O2 generation and radical receptors. Furthermore, this two-photon excitation strategy exhibits moderately broad substrate tolerance and single regioselectivity. We believe this operationally simple and sustainable catalytic system holds promising to inspire novel strategies for the value-added transformation of natural alkanes.

Author contributions

The authors confirm that their contributions to this paper are as follows: reaction design: Y. Liu; experimentation: Y. Liu, W. Wang, W. Xu, T. Pang and X. Wang; mechanism experiment and analysis: Y. Liu, Z. Chen, Q. Xu, Y. Zhang and P. Liu; and manuscript preparation: Y. Liu, Y. Zhang and P. Liu.

Conflicts of interest

There are no conflicts to declare. Experimental details and characterization data can be found in the SI. See DOI: https://doi.org/10.1039/d5gc02386f

Acknowledgements

We gratefully acknowledge the financial support for this work from the National Natural Science Foundation of China (No. 22162022), the Science and Technology Innovation Talents Program of Shihezi University (No. ZG010603), the Guidance Science and Technology Projects of the Corps (No. 2022ZD018), the Innovation Development Program of Shihezi University (CXFZ202204), the Tianshan Talents Program for Young Talents in Science and Technology Innovation (No. 2022TSYCCX0024), the Shanghai Cooperation Organization Science and Technology Partnership Program and the International Science and Technology Cooperation Program (No. 2022E01042).

References

  1. (a) D. S. Müller, N. L. Untiedt, A. P. Dieskau, G. L. Lackner and L. E. Overman, J. Am. Chem. Soc., 2015, 137, 660–663 CrossRef PubMed ; (b) A. L. G. Kanegusuku and J. L. Roizen, Angew. Chem., Int. Ed., 2021, 60, 21116–21149 CrossRef PubMed .
  2. (a) B. Giese and S. Lachhein, Angew. Chem., Int. Ed. Engl., 1981, 20, 967–967 CrossRef ; (b) B. Giese and J. Dupuis, Angew. Chem., Int. Ed. Engl., 1983, 22, 622–623 CrossRef ; (c) B. Giese, J. A. González-Gómez and T. Witzel, Angew. Chem., Int. Ed. Engl., 1984, 23, 69–70 CrossRef .
  3. X. S. Xue, P. Ji, B. Zhou and J. P. Cheng, Chem. Rev., 2017, 117, 8622–8648 CrossRef PubMed .
  4. (a) H. Cao, X. Tang, H. Tang, Y. Yuan and J. Wu, Chem Catal., 2021, 1, 523–598 Search PubMed ; (b) N. Holmberg-Douglas and D. A. Nicewicz, Chem. Rev., 2022, 122, 1925–2016 CrossRef PubMed ; (c) M. Galeotti, M. Salamone and M. Bietti, Chem. Soc. Rev., 2022, 51, 2171–2223 RSC ; (d) K. I. Goldberg and A. S. Goldman, Acc. Chem. Res., 2017, 50, 620 CrossRef PubMed ; (e) Z. Ye, Y. Yu, Y.-M. Lin, Y. Chen, S. Song and L. Gong, Nat. Synth., 2023, 2, 766 CrossRef ; (f) S. Cheng, Q. Li, X. Cheng, Y.-M. Lin and L. Gong, Chin. J. Chem., 2022, 40, 2825 CrossRef .
  5. (a) L. Capaldo, D. Ravelli and M. Fagnoni, Chem. Rev., 2022, 122, 1875–1924 CrossRef PubMed ; (b) H. Fan, Y. Fang and J. Yu, Chem. Commun., 2024, 60, 13796–13818 RSC ; (c) T. J. Fazekas, J. W. Alty, E. K. Neidhart, A. S. Miller, F. A. Lerbfarth and E. J. Alexanian, Science, 2022, 375, 545 CrossRef PubMed .
  6. (a) H.-P. Deng, Q. Zhou and J. Wu, Angew. Chem., Int. Ed., 2018, 57, 12661–12665 CrossRef CAS PubMed ; (b) A. Matsumoto, M. Yamamoto and K. Maruoka, ACS Catal., 2022, 12, 2045–2051 CrossRef CAS ; (c) B. Wang, C. A. Pettenuzzo, J. Singh, G. E. Mccabe, L. Clark, R. Young, J. Pu and Y. Deng, ACS Catal., 2022, 12, 10441–10448 CrossRef CAS ; (d) V. Carré, P. Godard, R. Méreau, H.-P. J. de Rouville, G. Jonusauskas, N. McClenaghan, T. Tassaing and J.-M. Vincent, Angew. Chem., Int. Ed., 2024, 63, e202402964 CrossRef ; (e) M. Wu, Z. Wu, H. T. Ang, B. Wang, T. Liu, S. Wu, Z. Lei, M. W. Liaw, S. Chanmungkalakul, C.-L. K. Lee, X. Liu, Y. Lu and J. Wu, ACS Catal., 2024, 14, 9364–9373 CrossRef CAS ; (f) L.-M. Entgelmeier, S. Mori, S. Sendo, R. Yamaguchi, R. Suzuki, T. Yanai, O. G. Mancheño, K. Ohmatsu and T. Ooi, Angew. Chem., Int. Ed., 2024, 63, e202404890 CAS ; (g) P. Jia, Q. Li, W. C. Poh, H. Jiang, H. Liu, H. Deng and J. Wu, Chem, 2020, 6, 1766 CrossRef CAS .
  7. (a) X.-Z. Fan, J.-W. Rong, H.-L. Wu, Q. Zhou, H.-P. Deng, J. D. Tan, C.-W. Xue, L.-Z. Wu, H.-R. Tao and J. Wu, Angew. Chem., Int. Ed., 2018, 57, 8514–8518 CrossRef CAS ; (b) H. Cao, D. Kong, L.-C. Yang, S. Chanmungkalakul, T. Liu, J. L. Piper, Z. Peng, L. Gao, X. Liu, X. Hong and J. Wu, Nat. Synth., 2022, 1, 794–803 CrossRef CAS .
  8. L. Capaldo, D. Merli, M. Fagnoni and D. Ravelli, ACS Catal., 2019, 9, 3054–3058 CrossRef .
  9. G. Laudadio, Y. Deng, K. van der Wal, D. Ravelli, M. Nuño, M. Fagnoni, D. Guthrie, Y. Sun and T. Noël, Science, 2020, 369, 92–96 CrossRef PubMed .
  10. (a) Q. An, L. Chang, H. Pan and Z. Zuo, Acc. Chem. Res., 2024, 57, 2915–2927 CrossRef ; (b) Q.-Y. Li, S. Cheng, Z. Ye, T. Huang, F. Yang, Y.-M. Lin and L. Gong, Nat. Commun., 2023, 14, 6366 CrossRef PubMed .
  11. (a) A. Hu, J.-J. Guo, H. Pan and Z. Zuo, Science, 2018, 361, 668–672 CrossRef PubMed ; (b) Q. An, Z. Wang, Y. Chen, X. Wang, K. Zhang, H. Pan, W. Liu and Z. Zuo, J. Am. Chem. Soc., 2020, 142, 6216–6226 CrossRef PubMed .
  12. Q. Yang, Y.-H. Wang, Y. Qiao, M. Gau, P. J. Carroll, P. J. Walsh and E. J. Schelter, Science, 2021, 372, 847–852 CrossRef .
  13. (a) S. M. Treacy and T. Rovis, J. Am. Chem. Soc., 2021, 143, 2729–2735 CrossRef PubMed ; (b) Y. C. Kang, S. M. Treacy and T. Rovis, ACS Catal., 2021, 11, 7442–7449 CrossRef PubMed .
  14. (a) Y. Jin, Q. Zhang, L. Wang, X. Wang, C. Meng and C. Duan, Green Chem., 2021, 23, 6984–6989 RSC ; (b) Y. Jin, L. Wang, Q. Zhang, Y. Zhang, Q. Liao and C. Duan, Green Chem., 2021, 23, 9406–9411 RSC ; (c) Q. Zhang, S. Liu, J. Lei, Y. Zhang, C. Meng, C. Duan and Y. Jin, Org. Lett., 2022, 24, 1901–1906 CrossRef PubMed .
  15. M. Yamane, Y. Kanzaki, H. Mitsunuma and M. Kanai, Org. Lett., 2022, 24, 1486–1490 CrossRef PubMed .
  16. (a) H. Bartling, A. Eisenhofer, B. König and R. M. Gschwind, J. Am. Chem. Soc., 2016, 138(36), 11860–11871 CrossRef PubMed ; (b) T. Zhang, X. Ren, B. Wang, W. Jin, Y. Xia, S. Wu, C. Liu and Y. Zhang, Org. Chem. Front., 2024, 11, 1050–1056 RSC ; (c) X. Ren, T. Zhang, B. Wang, W. Jin, Y. Xia, S. Wu, C. Liu and Y. Zhang, J. Org. Chem., 2024, 89, 5783–5796 CrossRef PubMed .
  17. F. Lan, C. Zhou, X. Huang, B. An and X. Zhang, Green Chem., 2022, 24, 2391–2396 RSC .
  18. S. Zhu, A. Das, L. Bui, H. Zhou, D. P. Curran and M. Rueping, J. Am. Chem. Soc., 2013, 135, 1823–1829 CrossRef PubMed .
  19. R. A. Aycock, C. J. Pratt and N. T. Jui, ACS Catal., 2018, 8, 9115–9119 CrossRef .
  20. (a) Y. Liu, H. Yan, Y. Chen, E. Hao and L. Shi, Chem. Commun., 2023, 59, 10388–10391 RSC ; (b) Y. Liu, Z. Wu, J.-R. Shan, H. Yan, E.-J. Hao and L. Shi, Nat. Commun., 2024, 15, 4374 CrossRef PubMed ; (c) Y. Wang, X. Zhou, T. Zhang, X. Ren, W. Xu, B. Wang, W. Jin, Y. Xia, C. Liu and Y. Zhang, Green Synth. Catal., 2024, 5, 319–323 Search PubMed ; (d) T. Zhang, X. Ren, J. Li, Y. Wang, B. Wang, Z. Chen, Y. Xia, S. Wu, C. Liu and Y. Zhang, Org. Lett., 2024, 26, 10259–10266 CrossRef PubMed ; (e) X. Zhou, W. Xu, B. Wang, A. Iqbal, Z. Chen, Y. Xia, W. Jin, C. Liu and Y. Zhang, J. Org. Chem., 2024, 89, 13345–13358 CrossRef PubMed ; (f) B. Wang, Y. Shao, Z. Chen, Y. Xia, F. Xue, W. Jin, S. Wu, Y. Zhang and C. Liu, Org. Lett., 2024, 26, 4329–4334 CrossRef PubMed ; (g) Q. Song, L. Zhang, B. Wang, Z. Chen, W. Jin, Y. Xia, S. Wu, C. Liu and Y. Zhang, Org. Lett., 2024, 26, 3685–3690 CrossRef PubMed ; (h) L. Shi, Y. Liu, X. Qi, R. Cao, Y. Zhu, J.-R. Shan, E.-J. Hao, Y. Jin and X. Feng, Chem. Commun., 2025, 61, 6352–6355 RSC .
  21. (a) W.-C. Xu, S. Sun and S. Wu, Angew. Chem., Int. Ed., 2019, 58, 9712–9740 CrossRef PubMed ; (b) G.-Z. Wang, D.-G. Liu, M.-T. Liu and Y. Fu, Green Chem., 2021, 23, 5082–5087 RSC .
  22. B. Niu, B. G. Blackburn, K. Sachidanandan, M. V. Cookea and S. Laulhé, Green Chem., 2021, 23, 9454–9459 RSC .
  23. (a) Q. Shen, J. Chen, X. Jing and C. Duan, Adv. Sci., 2024, 11, 2404293 CrossRef ; (b) Q. Shen, J. Chen, X. Jing and C. Duan, Angew. Chem., Int. Ed., 2025, 65, e202506277 Search PubMed .
  24. C. S. Foote, S. Wexler, W. Ando and R. Higgins, J. Am. Chem. Soc., 1968, 90, 975–981 CrossRef .

Footnote

† These authors contributed equally to this work.
This journal is © The Royal Society of Chemistry 2025
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