Dual visible-light and NHC-catalyzed radical relay trifunctionalization of unactivated alkenes
Abstract
Radical trifunctionalization of unactivated alkenes remains rare and challenging, although they can provide a robust tool for the construction of molecules with high added value from simple materials. This work presents the relay dual N-heterocyclic carbene organocatalytic and visible-light photocatalytic multi-component trifunctionalization of alkyl alkenes via the merger of remote 1,4-cyano migration and alkylacylation. The method features a broad substrate scope and good compatibility of diverse functional groups. Density functional theory calculations were also carried out to rationalize the origin of this reaction. The cooperative N-heterocyclic carbene and photoredox catalysis enabled reductive single-electron transfer reaction of acyl azolium species and subsequent radical-radical cross-coupling, allowing for the facile construction of three new C−C bonds in one-pot reactions with high regioselectivity.
Keywords
INTRODUCTION
The assembly of molecular frameworks by multi-step relay carbon-carbon bond cleavage and formation in a controlled and efficient manner has been at the heart of organic synthesis. Alkenes are readily available and inexpensive feedstocks that have been widely used for that purpose. Difunctionalization of alkenes presents numerous mature methods for accessing diverse-ranging molecules with high added value and structural complexity[1-6]. In comparison, the trifunctionalization of alkenes, particularly unactivated alkenes, is less explored and still poses a challenge. Recently, the appearance of radical functionalization of unactivated alkenes through the strategy of remote functional group migration (FGM)[7-10] provides an exceptional chance for the construction of trifunctionalized derivatives that are not accessible by other reactions [Scheme 1A]. Therefore, the discovery of new protocols for FGM reactions remains an important target and continues to be highly desirable for molecular assembly.
Scheme 1. Radical-mediated trifunctionalization of unactivated alkenes. FGM: Functional group migration; NHC: N-Heterocyclic carbene.
N-Heterocyclic carbene (NHC) catalysis[11-17] has emerged as one of the most powerful catalytic strategies in the field of organocatalysis, usually by means of a polarity-reversal mechanism. With the rapid development of photocatalysis [18-21], recent advances in single-electron transfer (SET)-based radical reactions have further broadened its reaction modes[22-28], offering otherwise inaccessible strategies compared to traditional
As a continuation of our studies on radical NHC-catalysis, our purpose herein is to realize the first reductive radical organocatalytic FGM reactions to fulfill trifunctionalization of hexenenitriles 3[70,71] via remote cyano migration[72-75]. Compared to the previous work using the NHC oxidative radical strategy, the substrate scope can enlarge to in-stock carboxylic acids and much more radical precursors. Thus, this protocol features a compatible dual catalytic system, mild reaction conditions, readily available substrates, excellent regioselectivity, and capability of late-stage functionalization, which will be favorable for molecular assembly [Scheme 1C].
RESULTS AND DISCUSSION
To start this work, commercially available sodium trifluoromethanesulfinate 1a was used as the trifluoromethyl radical precursor to investigate the feasibility of the reaction with 4-chlorobenzoic acid 2a and hexenenitrile 3a using DCE as the solvent, Cs2CO3 as a base, and Blue LEDs as light sources [Figure 1]. It is worth noting that the acid can be activated to produce benzoylimidazole 2a’in situ with
Figure 1. Optimization of the reaction conditiona. aUnless otherwise noted, 2a (0.4 mmol, 2.0 equiv.) and CDI (0.4 mmol, 2.0 equiv.) in DCE (1 mL) were typically stirred for 2 h. Then, the above solution was added to the mixture of 1a (0.4 mmol, 2.0 equiv.), 3a (0.2 mmol, 1.0 equiv.), NHC catalyst (0.03 mmol, 15 mol%), photocatalyst (0.01 mol, 5 mol%), and Cs2CO3 (0.4 mmol, 2.0 equiv.) in DCE (2 mL) which was irradiated under Blue LED typically for 24 h; bIsolated yields based on 2a, the dr was around 1/1 for all cases, and the dr was determined by 1H NMR; cThe reaction was conducted without N2 protection; d1 mmol scale; eK2CO3 as a base; ftriethylamine as a base; gDBU as a base. CDI: 1,1’-carbonyldiimidazole DBU; NHC: N-Heterocyclic carbene.
After screening different photosensitizers, it was found that the desired product 4a was produced in 72% yield with [Ir(dtbbpy)(ppy)2]PF6 as the photocatalyst (entry 3). Other photocatalysts, such as fac-Ir(ppy)3, 4CzIPN, and Br-4CzIPN, were inferior to the [Ir(dtbbpy)(ppy)2]PF6 (entries 4-7). Subsequently, we screened different NHC precursors, and NHC A was selected as the optimal organocatalyst to promote the reaction. Other NHCs B-D did not improve the reaction yields (entries 8-10). The nitrogen atmosphere protection was also essential for this reaction. The yield dropped to 45% when the reaction was conducted in the air (entry 11). Moreover, a scale-up (1 mmol) reaction was taken to afford product 4a in maintained yield (entry 12). Remarkably, only a trace of byproduct 4a’ was observed along the optimization process. At last, bases were screened, and a slightly decreased yield was observed with K2CO3. Organic bases were not suitable for this transformation.
With the optimal condition in hand, the generality of substrates was explored. We initially tested different acids 2 [Scheme 2]. Substituted benzoic acids bearing either halide or electron-donating groups at para positions of the benzoic acid were well compatible with the optimal condition, giving the products 4a-e in comparable yields. Slightly decreased yields were tracked when benzoic acids bearing electron-withdrawing groups 4f-h. Benzoic acids bearing meta substitution were also well tolerated under the standard conditions 4i-j. However, the more sterically hindered 2-methylbenzoic acid was not suitable for this reaction. Either
Scheme 2. Substrate scope for trifunctionalization of unactivated alkenes. CDI: 1,1’-carbonyldiimidazole.
The feasibility of installation of other radical precursors to the hexenenitrile 3d was also studied [Scheme 2, bottom]. Several sulfinate salts bearing a fluorinated alkyl group displayed good compatibility with the present system 4aa-ad. Sulfinate salts bearing a phenylsulfonyl substituted methyl group were also used as effective substrates, enabling the trifunctionalization of 3d to give product 4ae in an acceptable yield. However, sulfinate salts, such as sodium methanesulfinate, sodium ethanesulfinate, and other listed aliphatic sulfinates, did not deliver the desired products. Density functional theory (DFT) calculations were then taken into account for the possible reasons [Scheme 3]. To our interests, the activating energy of the corresponding radical added to the hexenenitrile significantly contributes to the success of the reaction. The reactions failed to yield the desired product when the activating energy was above 14.1 Kcal/mol. These findings might be helpful for prediction of the reactivity of other sulfinate salts.
Scheme 3. Activating energy calculation with different alkyl precursors.
To highlight the utility of this transformation, we undertook the derivatization of the ketone 4a [Scheme 4]. The alcohol 5 was synthesized using LiAlH4 as redundant in the yield of 83%. The cyano group within 4a can transform to amide to yield compound 6 with a mixed acid system (HOAc and H2SO4). In addition, the reaction of 4a with hydrazine could form hydrazone 6 in 80% yield.
Scheme 4. Application of the representative product.
Next, DFT calculations have been conducted to further prove the potential reaction mechanism and origin of the regioselectivity for 1,4-cyano migration [Figure 2].
Figure 2. Relative Gibbs free energy profiles of the reaction.
The combination of NHC-A (C1) generated from precatalyst A under basic conditions with benzoylimidazole 2a’ leads to NHC-bound acyl azolium C2. The SET process between C2 and CF3SO2Na proceeds smoothly to give transient trifluoromethyl radical and persistent NHC-bound ketyl radical C3. Subsequent addition of trifluoromethyl radical to hexenenitrile 3a produces intermediate S2 through the transition state TS1 (ΔG‡ = 9.8 kcal/mol). Whether the incident of 1,4-CN migration of TS1 occurs would decide the two possible pathways (path A, purple line vs. path B, blue line) for the radical-radical coupling. As described in the blue line, the direct radical-radical coupling of C3 with S2 yields intermediate S5 through transition state TS4 (ΔG‡ = 17.0 kcal/mol). The collapse of S5 gives birth to product 4a’ and NHC-A for the next catalytic cycle. In path A (purple line), the intramolecular radical addition of S2 to the cyano group forms a five-member imine radical intermediate S3 through transition state TS2 (ΔG‡ =
Based on these results, it can be concluded that the dual photocatalytic and NHC-promoted SET between sodium trifluoromethanesulfinate 1a and acyl azolium intermediate SA could simultaneously produce the NHC-derived radicals C3 and CF3 radicals. CF3 radicals were subsequently triggered by hexenenitriles 3 to obtain S2. The generated radical intermediate S2 may undergo remote 1,4-cyano migration via a cyclic intermediate S3 to yield radicals S4. The radical-radical cross-coupling with the persistent ketyl radical C3 and S2 or S4 would produce intermediate S5 and S7, respectively, which finally afford adducts 4a and byproduct 4a’ with the loss of NHC for the next catalytic cycle [Scheme 5].
Scheme 5. Plausible reaction pathway.
CONCLUSIONS
To sum up, we have described a novel protocol for trifunctionalization of unactivated hexenenitriles via merged NHC organocatalytic and photocatalytic radical relay alkylacylation. This reaction offers a generalizable and efficient strategy for molecular framework assembly, which involves multi-step C−C bond cleavage and formation by remote 1,4-cyano migration and alkylacylation. Theoretical calculations were used to both support the possible mechanism and figure out the origin of the regioselectivity for 1,4-CN migration.
DECLARATIONS
Authors’ contributions
Supervised the synthesis process: Feng J
Responsible for data collection and analysis: Feng JQ, Li L, Wang J, Ni A
Conducted calculations: Wei Z
Led the design and paper-writing efforts: Du D, Feng J
Availability of data and materials
NMR data for all the new compounds can be found in Supplementary Materials.
Financial support and sponsorship
This work was supported by the National Natural Science Foundation of China (Nos. 21572270, 21702232), the “Double First-Class” University Project of China Pharmaceutical University, and the College Students’ Innovative Entrepreneurial Training Plan Program.
Conflicts of interest
All authors declared that there are no conflicts of interest.
Ethical approval and consent to participate
Not applicable.
Consent for publication
Not applicable.
Copyright
© The Author(s) 2024.
Supplementary Materials
REFERENCES
1. Patel M, Ajay U, Padala K, Naveen T. Recent advances in cobalt-catalyzed functionalization of unactivated olefins. Asian J Org Chem 2022;11:e202200201.
2. DiPucchio RC, Rosca SC, Schafer LL. Hydroaminoalkylation for the catalytic addition of amines to alkenes or alkynes: diverse mechanisms enable diverse substrate scope. J Am Chem Soc 2022;144:11459-81.
3. Ghosh S, Patel S, Chatterjee I. Chain-walking reactions of transition metals for remote C−H bond functionalization of olefinic substrates. Chem Commun 2021;57:11110-30.
4. Li Y, Wu D, Cheng HG, Yin G. Difunctionalization of alkenes involving metal migration. Angew Chem Int Ed Engl 2020;59:7990-8003.
5. Giri R, Kc S. Strategies toward dicarbofunctionalization of unactivated olefins by combined heck carbometalation and cross-coupling. J Org Chem 2018;83:3013-22.
6. Badir SO, Molander GA. Developments in photoredox/nickel dual-catalyzed 1,2-difunctionalizations. Chem 2020;6:1327-39.
8. Chen YJ, Qu YL, Li X, Wang CC. Recent advances in 1,4-functional group migration-mediated radical fluoroalkylation of alkenes and alkynes. Org Biomol Chem 2020;18:8975-93.
9. Zhang G, Liu Y, Zhao J, Li Y, Zhang Q. Radical cascade reactions of unsaturated C-C bonds involving migration. Sci China Chem 2019;62:1476-91.
10. Wu X, Zhu C. Combination of radical functional group migration (FGM) and hydrogen atom transfer (HAT). Trends Chem 2022;4:580-3.
11. Chen XY, Gao ZH, Ye S. Bifunctional N-heterocyclic carbenes derived from l-pyroglutamic acid and their applications in enantioselective organocatalysis. Acc Chem Res 2020;53:690-702.
12. Mondal S, Yetra SR, Mukherjee S, Biju AT. NHC-catalyzed generation of α,β-unsaturated acylazoliums for the enantioselective synthesis of heterocycles and carbocycles. Acc Chem Res 2019;52:425-36.
13. Ohmiya H. N-heterocyclic carbene-based catalysis enabling cross-coupling reactions. ACS Catal 2020;10:6862-9.
14. Wang J, Zhao C, Wang J. Recent progress toward the construction of axially chiral molecules catalyzed by an N-heterocyclic carbene. ACS Catal 2021;11:12520-31.
15. Song R, Xie Y, Jin Z, Chi YR. Carbene-catalyzed asymmetric construction of atropisomers. Angew Chem Int Ed Engl 2021;60:26026-37.
16. Flanigan DM, Romanov-Michailidis F, White NA, Rovis T. Organocatalytic reactions enabled by N-heterocyclic carbenes. Chem Rev 2015;115:9307-87.
17. Zhen G, Jiang K, Yin B. Progress in organocatalytic dearomatization reactions catalyzed by N-heterocyclic carbenes. ChemCatChem 2022;14:e202200099.
18. Crespi S, Fagnoni M. Generation of alkyl radicals: from the tyranny of tin to the photon democracy. Chem Rev 2020;120:9790-833.
19. Pitre SP, Overman LE. Strategic use of visible-light photoredox catalysis in natural product synthesis. Chem Rev 2022;122:1717-51.
20. Yu XY, Chen JR, Xiao WJ. Visible light-driven radical-mediated C−C bond cleavage/functionalization in organic synthesis. Chem Rev 2021;121:506-61.
21. Zhang B, Wang J. Assembly of versatile fluorine-containing structures via N-heterocyclic carbene organocatalysis. Sci China Chem 2022;65:1691-703.
23. Song R, Chi YR. N-heterocyclic carbene catalyzed radical coupling of aldehydes with redox-active esters. Angew Chem Int Ed Engl 2019;58:8628-30.
24. Ishii T, Nagao K, Ohmiya H. Recent advances in N-heterocyclic carbene-based radical catalysis. Chem Sci 2020;11:5630-6.
25. Liu J, Xing XN, Huang JH, Lu LQ, Xiao WJ. Light opens a new window for N-heterocyclic carbene catalysis. Chem Sci 2020;11:10605-13.
26. Liu Q, Chen XY. Dual N-heterocyclic carbene/photocatalysis: a new strategy for radical processes. Org Chem Front 2020;7:2082-7.
27. Chen KQ, Sheng H, Liu Q, Shao PL, Chen XY. N-heterocyclic carbene-catalyzed radical reactions. Sci China Chem 2021;64:7-16.
28. Bay AV, Scheidt KA. Single-electron carbene catalysis in redox processes. Trends Chem 2022;4:277-90.
29. Guin J, De Sarkar S, Grimme S, Studer A. Biomimetic carbene-catalyzed oxidations of aldehydes using TEMPO. Angew Chem Int Ed Engl 2008;47:8727-30.
30. De Sarkar S, Grimme S, Studer A. NHC catalyzed oxidations of aldehydes to esters: chemoselective acylation of alcohols in presence of amines. J Am Chem Soc 2010;132:1190-1.
31. Zhang Y, Du Y, Huang Z, et al. N-heterocyclic carbene-catalyzed radical reactions for highly enantioselective β-hydroxylation of enals. J Am Chem Soc 2015;137:2416-9.
32. Wu X, Zhang Y, Wang Y, et al. Polyhalides as efficient and mild oxidants for oxidative carbene organocatalysis by radical processes. Angew Chem Int Ed Engl 2017;56:2942-6.
33. Ren SC, Lv WX, Yang X, et al. Carbene-catalyzed alkylation of carboxylic esters via direct photoexcitation of acyl azolium intermediates. ACS Catal 2021;11:2925-34.
34. Ishii T, Kakeno Y, Nagao K, Ohmiya H. N-heterocyclic carbene-catalyzed decarboxylative alkylation of aldehydes. J Am Chem Soc 2019;141:3854-8.
35. Ishii T, Ota K, Nagao K, Ohmiya H. N-heterocyclic carbene-catalyzed radical relay enabling vicinal alkylacylation of alkenes. J Am Chem Soc 2019;141:14073-7.
36. Kakeno Y, Kusakabe M, Nagao K, Ohmiya H. Direct synthesis of dialkyl ketones from aliphatic aldehydes through radical N-heterocyclic carbene catalysis. ACS Catal 2020;10:8524-9.
37. Ota K, Nagao K, Ohmiya H. N-heterocyclic carbene-catalyzed radical relay enabling synthesis of δ-ketocarbonyls. Org Lett 2020;22:3922-5.
38. Maki BE, Chan A, Phillips EM, Scheidt KA. Tandem oxidation of allylic and benzylic alcohols to esters catalyzed by N-heterocyclic carbenes. Org Lett 2007;9:371-4.
39. Maki BE, Scheidt KA. N-heterocyclic carbene-catalyzed oxidation of unactivated aldehydes to esters. Org Lett 2008;10:4331-4.
40. White NA, Rovis T. Enantioselective N-heterocyclic carbene-catalyzed β-hydroxylation of enals using nitroarenes: an atom transfer reaction that proceeds via single electron transfer. J Am Chem Soc 2014;136:14674-7.
41. White NA, Rovis T. Correction to “Oxidatively initiated NHC-catalyzed enantioselective synthesis of 3,4-disubstituted cyclopentanones from enals”. J Am Chem Soc 2015;137:13210.
42. Chen XY, Chen KQ, Sun DQ, Ye S. N-heterocyclic carbene-catalyzed oxidative [3 + 2] annulation of dioxindoles and enals: cross coupling of homoenolate and enolate. Chem Sci 2017;8:1936-41.
43. Dai L, Xia ZH, Gao YY, Gao ZH, Ye S. Visible-light-driven N-heterocyclic carbene catalyzed γ- and ϵ-alkylation with alkyl radicals. Angew Chem Int Ed Engl 2019;58:18124-30.
44. Dai L, Ye S. Photo/N-heterocyclic carbene co-catalyzed ring opening and γ-alkylation of cyclopropane enal. Org Lett 2020;22:986-90.
45. Zhang B, Peng Q, Guo D, Wang J. NHC-catalyzed radical trifluoromethylation enabled by togni reagent. Org Lett 2020;22:443-7.
46. Yang W, Hu W, Dong X, Li X, Sun J. N-heterocyclic carbene catalyzed γ-dihalomethylenation of enals by single-electron transfer. Angew Chem Int Ed Engl 2016;55:15783-6.
47. Kim I, Im H, Lee H, Hong S. N-heterocyclic carbene-catalyzed deaminative cross-coupling of aldehydes with Katritzky pyridinium salts. Chem Sci 2020;11:3192-7.
48. Li JL, Liu YQ, Zou WL, et al. Inside cover: radical acylfluoroalkylation of olefins through N-heterocyclic carbene organocatalysis (Angew. Chem. Int. Ed. 5/2020). Angew Chem Int Ed 2020;59:1746.
49. Yang HB, Wang ZH, Li JM, Wu C. Modular synthesis of α-aryl β-perfluoroalkyl ketones via N-heterocyclic carbene catalysis. Chem Commun 2020;56:3801-4.
50. Liu MS, Shu W. Catalytic, metal-free amide synthesis from aldehydes and imines enabled by a dual-catalyzed umpolung strategy under redox-neutral conditions. ACS Catal 2020;10:12960-6.
51. Jiang X, Li E, Chen J, Huang Y. Photo-induced energy transfer relay of N-heterocyclic carbene catalysis: an asymmetric α-fluorination/isomerization cascade. Chem Commun 2021:57;729-32.
52. Tan CY, Kim M, Hong S. Photoinduced electron transfer from xanthates to acyl azoliums: divergent ketone synthesis via N-heterocyclic carbene catalysis. Angew Chem Int Ed Engl 2023;62:e202306191.
53. Zeng R, Xie C, Xing JD, et al. Construction of alkenyl-isoquinolinones through NHC-catalyzed Remote C(sp3)-H acylation and cascade cyclization of benzamides and enals. Tetrahedron 2023;132:133239.
54. Du D, Zhang K, Ma R, et al. Bio- and medicinally compatible α-amino-acid modification via merging photoredox and N-heterocyclic carbene catalysis. Org Lett 2020;22:6370-5.
55. Chen L, Lin C, Zhang S, et al. 1,4-alkylcarbonylation of 1,3-enynes to access tetra-substituted allenyl ketones via an NHC-catalyzed radical relay. ACS Catal 2021;11:13363-73.
56. Bay AV, Fitzpatrick KP, Betori RC, Scheidt KA. Combined photoredox and carbene catalysis for the synthesis of ketones from carboxylic acids. Angew Chem Int Ed Engl 2020;59:9143-8.
57. Meng QY, Döben N, Studer A. Cooperative NHC and photoredox catalysis for the synthesis of β-trifluoromethylated alkyl aryl ketones. Angew Chem Int Ed Engl 2020;59:19956-60.
58. Zuo Z, Daniliuc CG, Studer A. Cooperative NHC/photoredox catalyzed ring-opening of aryl cyclopropanes to 1-aroyloxylated-3-acylated alkanes. Angew Chem Int Ed Engl 2021;60:25252-7.
59. Liu K, Studer A. Direct α-acylation of alkenes via N-heterocyclic carbene, sulfinate, and photoredox cooperative triple catalysis. J Am Chem Soc 2021;143:4903-9.
60. Wang P, Fitzpatrick KP, Scheidt KA. Combined photoredox and carbene catalysis for the synthesis of γ-aryloxy ketones. Adv Synth Catal 2022;364:518-24.
61. Meng QY, Lezius L, Studer A. Benzylic C-H acylation by cooperative NHC and photoredox catalysis. Nat Commun 2021;12:2068.
62. Sato Y, Goto Y, Nakamura K, Miyamoto Y, Sumida Y, Ohmiya H. Light-driven N-heterocyclic carbene catalysis using alkylborates. ACS Catal 2021;11:12886-92.
63. Wang X, Zhu B, Liu Y, Wang Q. Combined photoredox and carbene catalysis for the synthesis of α-amino ketones from carboxylic acids. ACS Catal 2022;12:2522-31.
64. Wang X, Yang R, Zhu B, et al. Direct allylic acylation via cross-coupling involving cooperative N-heterocyclic carbene, hydrogen atom transfer, and photoredox catalysis. Nat Commun 2023;14:2951.
65. Rourke MJ, Wang CT, Schull CR, Scheidt KA. Acyl azolium-photoredox-enabled synthesis of β-keto sulfides. ACS Catal 2023;13:7987-94.
66. Li S, Wang S, Feng H, et al. Visible-light-mediated NHC and tertiary amine catalysis enabling α-H acylation of alkenes. Org Lett 2023;25:3369-74.
67. Yang HB, Jin XF, Jiang HY, Luo W. Construction of C(CO)−C(CO) bond via NHC-catalyzed radical cross-coupling reaction. Org Lett 2023;25:1829-33.
68. Döben N, Reimler J, Studer A. Cooperative NHC/photoredox catalysis: three component radical coupling of aroyl fluorides, styrenes and alcohols. Adv Synth Catal 2022;364:3348-53.
69. Wang J, Wang Y, Li J, Wei Z, Feng J, Du D. Organocatalytic radical relay trifunctionalization of unactivated alkenes by a combination of cyano migration and alkylacylation. Chem Commun 2023;59:5395-8.
70. Guo K. Gu C. Li Y, et al. Photoredox catalyzed trifluoromethyl radical-triggered trifunctionalization of 5-hexenenitriles via cyano migration. Adv Synth Catal 2022;364:1388-93.
71. Wu Z. Ren R. Zhu C. Combination of a cyano migration strategy and alkene difunctionalization: the elusive selective azidocyanation of unactivated olefins. Angew Chem Int Ed Engl 2016;55:10821-4.
72. Ji M, Wu Z, Yu J, Wan X, Zhu C. Cyanotrifluoromethylthiolation of unactivated olefins through intramolecular cyano migration. Adv Synth Catal 2017;359:1959-62.
73. Ren R, Wu Z, Huan L, Zhu C. Synergistic strategies of cyano migration and photocatalysis for difunctionalization of unactivated alkenes: synthesis of Di- and mono-fluorinated alkyl nitriles. Adv Synth Catal 2017;359:3052-6.
74. Wang N, Li L, Li ZL, et al. Catalytic diverse radical-mediated 1,2-cyanofunctionalization of unactivated alkenes via synergistic remote cyano migration and protected strategies. Org Lett 2016;18:6026-9.
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Feng, J. Q.; Li L.; Wang J.; Ni A.; Wei Z.; Du D.; Feng J. Dual visible-light and NHC-catalyzed radical relay trifunctionalization of unactivated alkenes. Chem. Synth. 2024, 4, 5. http://dx.doi.org/10.20517/cs.2023.43
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