Electrochemical Rhodium-Catalyzed Enantioselective C–H Annulation with Alkynes

Abstract

Open AccessCCS ChemistryRESEARCH ARTICLE5 Sep 2022Electrochemical Rhodium-Catalyzed Enantioselective C–H Annulation with Alkynes Yuan-Qiong Huang, Zhi-Jie Wu, Li Zhu, Qing Gu, Xiaojie Lu, Shu-Li You and Tian-Sheng Mei Yuan-Qiong Huang State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032 State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Pudong, Shanghai 201203 , Zhi-Jie Wu State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032 , Li Zhu State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032 , Qing Gu State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032 , Xiaojie Lu *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Drug Research, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Pudong, Shanghai 201203 , Shu-Li You *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032 and Tian-Sheng Mei *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] E-mail Address: [email protected] State Key Laboratory of Organometallic Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Shanghai 200032 https://doi.org/10.31635/ccschem.021.202101376 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail The synergistic use of transition metal catalysis and electrochemistry is an attractive strategy for oxidative site-selective C–H functionalization since the use of stoichiometric chemical oxidants can be avoided and novel reactivity can be achieved. However, metal-catalyzed electrochemical C–H functionalization is mainly limited to arene C(sp2)–H functionalization, and enantioselective C–H functionalization is uncommon and remains challenging. Herein, we report an electrochemically tuned rhodium-catalyzed enantioselective C–H annulation with alkynes, affording various spiropyrazolones in good yields and enantioselectivity in an undivided cell at room temperature. Notably, unsymmetrical alkylarylacetylenes are also efficiently converted to their corresponding spiroannulation products with excellent regioselectivity and good enantioselectivity. Thus, the protocol provides a practical and environmentally benign tool for forging chiral spiropyrazolones, which are important structural motifs found in pharmaceuticals and biologically active molecules. Download figure Download PowerPoint Introduction Organic electrosynthesis has emerged as an appealing and effective strategy for achieving challenging transformations with diminished waste generation via the utilization of electric current as a redox agent.1–7 Among many electrochemical transformations, metal-catalyzed oxidative C–H functionalization represents one of the most promising reaction types,8–12 wherein electric current is used to turnover catalysts and stoichiometric chemical oxidant is avoided. However, this transformation is predominantly restricted to arene C–H functionalization.13–25 To date, only limited examples have been discovered for electrochemical vinylic26,27 or alkane C–H functionalization,28–30 presumably due to their harsh conditions to activate corresponding C–H bonds and chemoselectivity issues. Furthermore, metal-catalyzed enantioselective electrochemical C–H functionalization is rare.31 Achieving high enantioselectivity in metal-catalyzed electrochemical C–H functionalization is problematic due the following: (1) electrolytes are typically destructive for stereocontrol; (2) high electrode potentials are necessary to generate high-valence oxidation states of metal catalysts, which may lead to side reactions; (3) metal catalysts can be deactivated or participate in reduction at the cathode in an undivided cell. Chiral spiropyrazolones are essential structural motifs found in biologically active molecules and pharmaceuticals,32,33 including antitumor and antibacterial agents (Figure 1a).34–37 Among the various methods to synthesize these targets, metal-catalyzed C–H functionalization is perhaps the most straightforward way. For instance, Yao and co-workers38 demonstrated Rh-catalyzed oxidative C–H annulation of α-arylidene pyrazolone with alkynes using Cu(OAc)2 as a terminal oxidant. Later, Waldmann and co-workers39 reported an enantioselective spiroannulation, where long reaction times, an inert atmosphere, and stoichiometric amounts of chemical oxidant were required (Figure 1b). Developing an environmentally friendly alternative to established approaches like these is an appealing and challenging task for chemists. Aligned with our continued interest in asymmetric organotransition metal-catalyzed electrochemistry,40–43 herein, we report a novel Rh-catalyzed enantioselective electrochemical synthesis of spiropyrazolones via C–H annulation with alkynes in an undivided cell at room temperature (Figure 1c). Figure 1 | (a–c) Representative biologically active pyrazolone derivatives and Rh-catalyzed C–H annulation with alkynes. Download figure Download PowerPoint Experimental Methods General procedure for the electrochemical Rh-catalyzed enantioselective synthesis of spiropyrazolones Electrocatalysis was carried out in an IKA ElectraSyn 2.0 equipped with reticulated vitreous carbon (RVC) (0.2 cm × 0.8 cm × 3.0 cm) as the anode and Pt as the cathode (0.8 cm × 3.0 cm). α-Arylidene pyrazolones 1 (0.2 mmol, 2.0 equiv), alkyne 2 (0.1 mmol, 1.0 equiv), n-Bu4NPF6 (0.15 mmol, 1.5 equiv), cat-1 (10 mol %), and benzoyl peroxide (BPO) (10 mol %) were dissolved in MeOH (7.0 mL). Electrocatalysis was performed at room temperature at a constant voltage of 1.2 V maintained for 5 h. After the reaction, the mixture was concentrated in vacuo. The resulting residue was purified by silica gel flash chromatography to give the annulation product. More experimental procedures and a photographic guide for electrochemical C–H annulation are provided in the Supporting Information. Results and Discussion We commenced our study by selecting α-arylidene pyrazolone 1a and diphenylacetylene 2a as model substrates, 4 mol % [Cp*RhCl2]2 as a catalyst, and 3 equiv of n-Bu4NOAc as an electrolyte in MeOH at room temperature for 3 h. We found that 89% isolated yield of spiropyrazolone 3 could be obtained (Table 1, entry 1). Control experiments showed that the Rh catalyst and electric current are both essential for this reaction (Table 1, entries 2 and 3). Increasing the reaction temperature afforded a comparable yield to that of room temperature (Table 1, entries 4 and 5). Other different electrode materials induced a lower yield (Table 1, entries 6–8). Using CH3CN, instead of MeOH, as the solvent resulted in slightly lower yield (Table 1, entry 9). When using 2 mol % [Cp*RhCl2]2 as a catalyst, 65% isolated yield of spiropyrazolone 3 could be obtained (Table 1, entry 10). Under an inert atmosphere, the reaction was not affected and spiropyrazolone 3 was obtained in 89% isolated yield (Table 1, entry 11). Table 1 | Optimization of Reaction Conditionsa Entry Variation from Standard Conditions Yield (%)b 1 None 89 2 No [Cp*RhCl2]2 — 3 No electric content — 4 60 °C 93 5 40 °C 91 6 Graphite instead of RVC 78 7 Pt instead of RVC 50 8 Ni foam instead of RVC 71 9 CH3CN instead of MeOH 84 10 2 mol % [Cp*RhCl2]2 65 11 N2 89 aReaction conditions: 1a (0.1 mmol), 2a (1.5 equiv), [Cp*RhCl2]2 (4 mol %), n-Bu4NOAc (3.0 equiv), MeOH (4 mL) in undivided cell, I = 1.5 mA, 3 h. bYields of isolated product. With optimized conditions in hand, internal alkynes bearing different substituents on the aromatic ring were first investigated (Figure 2). Results showed that either electron-donating groups such as methyl ( 11), ethyl ( 6), amyl ( 7), isopropyl ( 8), and tert-butyl ( 9) or electron-withdrawing groups such as F ( 4, 13), Cl ( 5, 12), and CF3 ( 10) were compatible with the reaction, providing the corresponding products in 70–92% yield. With unsymmetrical internal alkynes ( 14– 22), excellent regioselectivity (>20:1) and moderate to good yields (64–83%) were achieved. Next, we investigated the scope of substituted α-arylidene pyrazolones ( 23– 46) under optimized reaction conditions. Para- and meta-substitution of R3 in the α-arylidene pyrazolones with various functional groups (such as halide, alkyl, ether, trifluoromethyl, ester, piperonyl, and 2-naphthyl groups) were amenable to this protocol, furnishing the desired products in 65–81% yields. A variety of substituents on the designated R1 or R2 positions of the α-arylidene pyrazolones did not significantly alter the reaction efficiency, affording the corresponding products ( 37– 45) in good yield (70–83%). Notably, R2 is typically required to include aromatic rings, since alkyl substituents, such as methyl groups, only provide 18% yield in the previous report using Cu(OAc)2 as the chemical oxidant.38 However, the methyl group is well tolerated in this electrochemical system, affording 46 in 81% yield. This indicates that this Rh-catalyzed electrochemical C–H annulation provides a valuable alternative to the synthesis of spiropyrazolones. Figure 2 | Rh-catalyzed electrochemical C–H annulation with alkynes. Reaction conditions: 1a (0.1 mmol), 2a (1.5 equiv), [Cp*RhCl2]2 (4 mol %), n-Bu4NOAc (3.0 equiv), MeOH (4 mL) in an undivided cell, I = 1.5 mA, 3 h. Download figure Download PowerPoint Development of enantioselective C–H annulation The mildness of the racemic coupling shows potential in the development of an asymmetric system. The impact of different Cpx ligands was first investigated. Initially, we chose α-arylidene pyrazolone 1a and diphenylacetylene 2a as model reactants under constant-current electrolysis at 1.5 mA in the presence of 10 mol % BPO (to oxidize the Rh(I) catalyst or facilitate C–H bond activation)44–46 and 3.0 equiv of n-Bu4NOAc in MeOH in an undivided cell to survey various chiral catalysts for this reaction (Table 2). The Cramer group44–49 demonstrated that 1,1′-binaphthol (BINOL)-derived CpxRh complexes are privileged chiral ligands for asymmetric synthesis. Using the BINOL-derived CpxRh complex cat-1 (10 mol %) as the catalyst, the desired spiropyrazolone 3 was obtained in 29% yield and with excellent enantioselectivity (97:3 er). Evaluation of a diverse array of other CpxRh catalysts ( cat-2–cat-5) did not reveal better results (30%–35% yields, 90.5:9.5–93:7 er). The spiro SCpxRh complexes were ineffective,50 leading to lower yield and enantioselectivity of 3 (≤15%, 89:11–94:6 er) ( cat-6–cat-8). Piperidine-fused CpxRh catalyst reported by Waldmann et al.39 also gave relatively low yields and enantioselectivity (25% yield, 93:7 er) in electrochemical C–H annulation ( cat-9). Next, we probed various reaction conditions using α-arylidene pyrazolone 1a and diphenylacetylene 2a as reaction partners. To our delight, using cat-1 as the catalyst, BPO as the additive, n-Bu4NPF6 as the electrolyte, and MeOH as the solvent in an undivided cell with reticulated vitreous carbon (RVC) as the anode and Pt as the cathode under constant 1.2 V for 5 h at room temperature, the spiroannulation product 3 was obtained in good yield and enantioselectivity (71% yield, 94:6 er, Table 2, entry 1). Control experiments indicated that the Rh catalyst, electric current, and BPO are all required for this reaction (Table 2, entries 2–4). The addition of hexafluoroisopropanol (HFIP) or H2O to the electrochemical cell diminished the yield but did not significantly impact the enantioselectivity (Table 2, entries 5 and 6). Both the yield and enantioselectivity diminished significantly when other solvents were used (Table 2, entries 7 and 8). When the reaction was conducted under constant current instead of constant voltage, 3 was obtained in 63% yield and 95:5 er (Table 2, entry 9). The absolute configuration of product 3 was determined to be S as compared to Waldmann et al.39 Table 2 | Optimization of Chiral Catalysts Entry Variation from Standard Conditionsb Yield (%)d er 1 None 71 94:6 2 No cat-1 — — 3 No electric current — — 4 No BPO — — 5 Addition of 1 equiv HFIP 48 93:7 6 Addition of 10 equiv H2O 40 94:6 7 CH3CN instead of MeOH 42 91:9 8 CH3CN/MeOH (1:1, V:V) instead of MeOH 45 91:9 9c Constant current instead of constant voltage 63 95:5 aReaction conditions: 1a (0.1 mmol), 2a (1.5 equiv), CpxRh (10 mol %), BPO (10 mol %), n-Bu4NOAc (3.0 equiv), MeOH (3.0 mL), in an undivided cell with RVC as anode and Pt as cathode (each 1.0 cm × 1.0 cm), 1.5 mA. bStandard conditions: 1a (2.0 equiv), 2a (0.1 mmol), cat-1 (10 mol %), BPO (10 mol %), n-Bu4NPF6 (1.5 equiv), MeOH (7 mL) in IKA ElectraSyn 2.0, U = 1.2 V. c 1a (0.1 mmol), 2a (1.5 equiv), cat-1 (10 mol %), BPO (10 mol %), n-Bu4NPF6 (2.0 equiv), MeOH (7.0 mL) in IKA ElectraSyn 2.0, I = 1.5 mA. dYields of isolated product. With the optimized reaction conditions in hand, we evaluated the alkyne scope (Figure 3). Symmetrical diarylacetylenes with varying electronic properties were all found to be suitable for the reaction and gave 4– 46 in moderate to good yield and enantioselectivity (45–82% yields and 89.5:10.5–94:6 er). Of note, para-substitution with i-Pr and t-Bu gave the desired products ( 8 and 9) in good yields (80% and 82% yields, respectively) and moderate enantioselectivities (91.5:8.5 and 89.5:10.5 er, respectively). Ortho- and meta-substitution afforded similar results under standard conditions, delivering the products in 60–78% yields and 91:9–94:6 er ( 11– 13). 1-Phenyl-1-hexyne ( 14) and other unsymmetrical alkynes bearing bromide ( 15), ether ( 16), ester ( 17), or trifluoromethyl groups ( 18) on the benzene ring were all tolerated well, affording the desired products 14– 18 in good regio- and enantioselectivity (58–70% yields and 91:9–92.5:7.5 er). In addition, unsymmetrical alkylarylacetylenes 2q– 2t were also efficiently converted to the corresponding spiroannulation products ( 19– 22) with excellent regioselectivity and good enantioselectivity. A direct comparison of our electrochemical conditions to the non-electrochemical conditions previously described for the utilization of cat-939 (including an inert atmosphere) demonstrates the superior catalytic efficiency of this electrochemical variant, particularly the shorter reaction time ( 12, 15, 33, 37, and 44). Next, we investigated the scope of substituted α-arylidene pyrazolones under optimized reaction conditions (Figure 3). A variety of α-arylidene pyrazolones afforded the corresponding desired products in good yield and enantioselectivity. Para-substitution of R3 in the α-arylidene pyrazolones with various functional groups such as halide, alkyl, ether, trifluoromethyl, and ester groups was well-tolerated under standard conditions, affording the desired products 23– 29 in 55–64% yields and 89:11–94:6 er. The chloro and bromo substituents in products 24 and 25 provided a convenient handle for further transformation. Acetal-protected 30 was formed in 71% yield and 93:7 er. Ortho- or meta-substitution of R3 in α-arylidene pyrazolones with halides or trifluoromethyl groups such as 2-fluoro, 2-chloro, 3-fluoro, and 3-trifluoromethyl were also well tolerated in this reaction ( 31– 34, 67–73% yield, 88:12–94:6 er), though the ortho-substituted variants 31 and 32 were produced with lower enantioselectivity (88:12 and 85:15 er, respectively), perhaps as a result of the steric encumbrance. Di-substitution with a 3-Me-4-Cl on the benzene ring afforded product 36 in 58% yield and 94:6 er. In addition, naphthyl-containing 35 was delivered in 70% yield and 93:7 er. A variety of substituents on the designated R1 or R2 groups of the α-arylidene pyrazolones did not significantly alter the reaction efficiency and enantioselectivity, affording the corresponding products in good yield and enantioselectivity (56–72% yield and 91:9–94:6 er). Interestingly, R2 need not be aromatic in nature, as a methyl group afforded 46 in 66% yield and 94:6 er. Figure 3 | Rh-catalyzed electrochemical C–H annulation with alkynes. Reaction conditions: 1 (2.0 equiv), 2 (0.1 mmol), cat-1 (10 mol %), BPO (10 mol %), n-Bu4NPF6 (1.5 equiv), MeOH (7 mL) in IKA ElectraSyn 2.0, U = 1.2 V, 5 h. a1 (2.0 equiv), 2 (0.1 mmol), cat-9 (10 mol %), Cu(OAc)2 (2.0 equiv), MeOH (4 mL) at 0 °C under inert atmosphere for 72 h. Download figure Download PowerPoint Mechanistic study To gain further insight into the electrochemical asymmetric spiroannulation mechanism, we conducted cyclic voltammetric studies of cat-1, reactants 1a and 2a, and product 3 at ambient temperature (Figure 4). We observed irreversible oxidation of cat-1 at 0.44 and 1.65 V versus saturated calomel electrode (SCE), whereas [Cp*RhCl2]2 exhibited oxidation peaks at 1.58 V versus SCE. Reactants 1a and 2a and product 3 exhibit oxidation peaks at 1.53, 1.90, and 1.57 V versus SCE, respectively. These results indicate that cat-1 is oxidized preferentially under anodic oxidation. Figure 4 | Cyclic voltametric study. Conditions: Cyclic voltammograms recorded on a glassy carbon electrode (area = 0.03 cm2) at ambient temperature. The scan rate was 100 mV s−1. (a) MeCN containing 0.1 M of n-Bu4NPF6. (b) MeCN containing 0.1 M of n-Bu4NPF6, after addition of 5.0 mM cat-1. (c) MeCN containing 0.1 M n-Bu4NPF6, after addition of 5.0 mM of [Cp*RhCl2]2. (d) MeCN containing 0.1 M of n-Bu4NPF6, after addition of 5.0 mM of 3aa. (e) MeCN containing 0.1 M of n-Bu4NPF6, after addition of 5.0 mM of 1a. (f) MeCN containing 0.1 M of n-Bu4NPF6, after addition of 10 mM of 2a. Download figure Download PowerPoint On the basis of our mechanistic studies and literature reports,38,39 a plausible catalytic cycle is shown in Figure 5. Initially, tautomerization of reactant 1 generates dienol 1′, which undergoes C–H bond cleavage to afford the six-membered cyclometalated CpxRh(III) intermediate A. Coordination of alkyne 2 to the rhodium center and regioselective migratory insertion into the Rh–C bond generates the eight-membered rhodacycle intermediate B. Due to the unfavorable steric interaction between R1 and R3, B may undergo isomerization to generate intermediate C, which then undergoes the C–C bond reductive elimination to offer the spirocyclic product 3. The CpxRh(III) catalyst is regenerated after anodic oxidation. Figure 5 | Rh-catalyzed electrochemical C–H annulation with alkynes. Download figure Download PowerPoint Conclusion We have demonstrated the first example of the Rh-catalyzed enantioselective electrochemical synthesis of spiropyrazolones via C–H annulation with alkynes in undivided cells. The method affords a variety of chiral spiropyrazolones in good yields and enantioselectivities. The protocol is operationally simple and robust and can be operated with IKA ElectraSyn 2.0. Preliminary mechanistic experiments showed that oxidation-induced reductive elimination is crucial for spiroannulation with concomitant release of the product. Further efforts to develop transition metal-catalyzed enantioselective electrochemical C–H functionalization are currently underway in our laboratory. Supporting Information Supporting Information is available and includes experimental procedure and compound characterization data. Conflict of Interest There is no conflict of interest to report. Funding Information This research was made possible as a result of a generous grant from NSFC (nos. 21821002, 21772222, and 91956112), CAS (no. XDB20000000), and Science and Technology Commission of Shanghai Municipality (nos. 18JC1415600 and 20JC1417100). Dedication This paper is dedicated to the 100th anniversary of Chemistry at Nankai University. References 1. Wang F.; Stahl S. S.Electrochemical Oxidation of Organic Molecules at Lower Overpotential: Accessing Broader Functional Group Compatibility with Electron–Proton Transfer Mediators.Acc. Chem. Res.2020, 53, 561–574. Google Scholar 2. Siu J. C.; Fu N.; Lin S.Catalyzing Electrosynthesis: A Homogeneous Electrocatalytic Approach to Reaction Discovery.Acc. Chem. Res.2020, 53, 547–560. Google Scholar 3. Jing Q.; Moeller K. D.From Molecules to Molecular Surfaces. Exploiting the Interplay between Organic Synthesis and Electrochemistry.Acc. Chem. Res.2020, 53, 135–143. Google Scholar 4. Kingston C.; Palkowitz M. D.; Takahira Y.; Vantourout J. C.; Peters B. K.; Kawamata Y.; Baran P. S.A Survival Guide for the “Electro-Curious”.Acc. Chem. Res.2020, 53, 72–83. Google Scholar 5. Röckl J. L.; Pollok D.; Franke R.; Waldvogel S. R.A Decade of Electrochemical Dehydrogenative C,C-Coupling of Aryls.Acc. Chem. Res.2020, 53, 45–61. Google Scholar 6. Xiong P.; Xu H.-C.Chemistry with Electrochemically Generated N-Centered Radicals.Acc. Chem. Res.2019, 52, 3339–3350. Google Scholar 7. Yong Y.; Lei A.Electrochemical Oxidative Cross-Coupling with Hydrogen Evolution Reactions.Acc. Chem. Res.2019, 52, 3309–3324. Google Scholar 8. Jiao K.-J.; Xing Y.-K.; Yang Q.-L.; Qiu H.; Mei T.-S.Site-Selective C–H Functionalization via Synergistic Use of Electrochemistry and Transition Metal Catalysis.Acc. Chem. Res.2020, 53, 300–310. Google Scholar 9. Ackermann L.Metalla-Electrocatalyzed C–H Activation by Earth-Abundant 3d Metals and Beyond.Acc. Chem. Res.2020, 53, 84–104. Google Scholar 10. Kakiuchi F.; Kochi T.New Strategy for Catalytic Oxidative C–H Functionalization: Efficient Combination of Transition Metal Catalyst and Electrochemical Oxidation.Chem. Lett.2020, 49, 1256–1269. Google Scholar 11. Ma C.; Fang P.; Mei T.-S.Recent Advances in C–H Functionalization Using Electrochemical Transition Metal Catalysis.ACS Catal.2018, 8, 7179–7189. Google Scholar 12. Sauerman N.; Meyer T. H.; Qiu Y.; Ackermann L.Electrocatalytic C–H Activation.ACS Catal.2018, 8, 7086–7103. Google Scholar 13. Amatore C.; Cammoun C.; Jutand of in the from Google Scholar Kakiuchi F.; Kochi H.; N.; C–H with Hydrogen by of Electrochemical Chem. Google Scholar Y.; T. of J. Google Scholar Mei R.; N.; J. Ackermann for Activation with Chem. Google Scholar N.; Meyer T. H.; C.; Ackermann C–H at Chem. Google Scholar Wang P.; L.; Lei C–H of with Chem. Google Scholar Wang D.; Y.; L.; Lei Annulation with or Google Scholar Wu F.; Lin Xu C–H by Oxidation Chem. Google Scholar Xu F.; Li Huang C.; Xu Electrochemical Dehydrogenative Catal.2018, 8, Google Scholar Li Annulation of with Entry to Google Scholar Yang Q.-L.; Wang Lu Fang P.; Mei Electrochemical C–H of with Chem. Google Scholar L.; Electrochemical Functionalization of with Google Scholar of C–H of with via Google Scholar Yang Q.-L.; Xing Y.-K.; Wang Ma Yang Mei C–H Chem. Google Scholar Xing Y.-K.; Yang Q.-L.; Mei Rhodium-Catalyzed Electrochemical C–H Annulation of with 12, Google Scholar Yang Q.-L.; Li Ma C.; Fang P.; Mei via Electrochemical Chem. Google Scholar A. L.; M. via Electrochemical Google Scholar S. J. B. C.; S. N.; M. S.Electrochemical of in Lett.2020, Google Scholar C.; J. J. P.; Ackermann C–H Activation by to Chem. Google Scholar M. Synthesis of or Google Scholar P.; Synthesis of and the of Google Scholar D.; H.; and Use as Google Scholar Y.; Wang C.; Huang P.; C.; of in Synthesis of as Chem. 5, Google Scholar M. P.; S. K.; M. T. M. P.; J. J. C.; J. F.; M. C.; Xu S. C.; L.; M. S. K. K.; K.; M. of as of Google Scholar Wu Li Y.; Xu Y.; N.; C.; H.; with Synthesis and J. Google Scholar Li P.; Gu Lin Yao of by C–H Google Scholar Li R.; C.; A. P.; Waldmann Activation in the Synthesis of Chem. Google Scholar Qiu H.; Wang D.; Ma Mei Electrochemical Synthesis of Chem. Google Scholar Wang C.; You Mei Enantioselective of Cyclic Chem. Google Scholar Jiao K.-J.; Li Xu Li K.; Mei of with Chem. 5, Google Scholar Wang Xu Wang Fang P.; Mei in J. Google Scholar Wang Y.; Cramer C–H Functionalization by of and Chem. Google Scholar Y.; Cramer C–H Activation to Cyclic Chem. Google Scholar Cramer of Chiral for Enantioselective C–H of Chem. Google Scholar Cramer as in C–H Google Scholar D.; Cramer by Chiral Chem. Google Scholar Cramer for C–H Chem. Google Scholar C.; You and of Chiral in Rhodium-Catalyzed Oxidative of with Chem. Google Scholar Information Chinese C–H electrochemistry

Topics & Concepts