Copper-Catalyzed Decarboxylative Oxyalkylation of Alkynyl

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Copper-Catalyzed Decarboxylative Oxyalkylation of Alkynyl Carboxylic Acids: Synthesis of γ‑Diketones and γ‑Ketonitriles Yi Li,† Jia-Qi Shang,† Xiang-Xiang Wang,† Wen-Jin Xia,† Tao Yang,† Yangchun Xin,‡ and Ya-Min Li*,† †

Faculty of Life Science and Technology, Kunming University of Science and Technology, Kunming 650500, P.R. China Katzin Diagnostic & Research PET/MR Center, Nemours/Alfred I. DuPont Hospital for Children, Wilmington, Delaware 19803, United States

‡

Org. Lett. Downloaded from pubs.acs.org by EAST CAROLINA UNIV on 03/14/19. For personal use only.

S Supporting Information *

ABSTRACT: A novel copper-catalyzed decarboxylative oxyalkylation of alkynyl carboxylic acids with ketones and alkylnitriles via direct C(sp3)−H bond functionalization to construct new C−C bonds and C−O double bonds was developed. This transformation is featured by wide functional group compatibility and the use of readily available reagents, thus affording a general approach to γ-diketones and γ-ketonitriles. A possible mechanism is proposed. γ-Diketones1 and γ-ketonitriles2 are important synthetic building blocks for many biologically significant compounds and pharmaceuticals. γ-Diketones are also well-known versatile precursors for the synthesis of five-membered heteroarenes (Paal−Knorr reaction). Thus, numerous methods have been developed for the construction of γ-diketones and γketonitriles,3,4 and among them, introducing the carbonyl or cyanomethyl group through a direct C(sp3)−H functionalization of ketones or alkylnitriles has attracted considerable attention owing to the avoidance of prefunctionalization, exclusion of strong bases, and high atom economy.5−7 Wang et al. reported that two ketones underwent an oxidative coupling at their α-position to build the γ-diketones in the presence of copper or silver salt.5a,b Carbo-carbonylation of arylalkenes with ketones via a SOMO-enamine was also developed to construct γ-diketones by Huang and Xie.5c Wang, Xing, and co-workers reported the oxidative coupling of ketones with alkenes via C(sp3)−H bond functionalization by a copper/ manganese catalytic system to form γ-diketones.5d The direct oxidative coupling of alkenes with alkyl nitriles has also been developed to construct γ-ketonitriles.6a Very recently, Wu, Kim, and co-workers reported a 1,4-refunctionalization of βdiketones with alkyl nitriles by iron catalysis for the synthesis of γ-ketonitriles.6b Despite these advances, developing an efficient and general method to construct γ-diketones and γketonitriles is still in need. Decarboxylative-coupling reactions is one of the most powerful synthetic strategies for the formation of C−C and C−heteroatom bonds.8 Compared with terminal alkynes, alkynyl carboxylic acids are more convenient to handle and synthesize, and their use as surrogates for terminal alkynes has thus drawn much attention in recent years. Much effort has © XXXX American Chemical Society

been made to construct C−C,9 C−N,10 C−P,11 C−B,12 C− Si,13 and C−S14 bonds by the decarboxylative coupling reactions of alkynyl carboxylic acids. The decarboxylative difunctionalization of alkynyl carboxylic acids, such as oxytrifluoromethylation,9c iodofluoroalkylation,9f nitroaminoxylation,10c oxyphosphination,11c hydroxysulfonylation,14e,f and disulfonylation,15b were also achieved. However, the decarboxylative oxyalkylation of alkynyl carboxylic acids remained underexplored. As part of our interest in C(sp3)−H bond functionalization and decarboxylative coupling,15 herein we present a novel and general decarboxylative oxyalkylation of alkynyl carboxylic acids with ketones and alkylnitriles to construct γ-diketones and γ-ketonitriles, respectively (Scheme 1). Scheme 1. Decarboxylative Oxyalkylation of Alkynyl Carboxylic Acids

Initially, the reaction of phenylpropiolic acid 1a with acetone 2a (both as reactant and solvent) was carried out as the model for the optimization of reaction conditions. When phenylpropiolic acid was treated with acetone in the presence of Cu(ClO4)2·6H2O (10 mol %) and K2S2O8 (3.0 equiv) with H2O as cosolvent at 80 °C, the desired γ-diketone 3a was Received: February 9, 2019

A

DOI: 10.1021/acs.orglett.9b00520 Org. Lett. XXXX, XXX, XXX−XXX

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drawing groups (Me, MeO, AcNH, F, Cl, Br, NO2, CN, Ac, and CO2Me) on the aromatic ring reacted well with acetone to afford the γ-diketones in moderate to good yields (3a−s). What’s more, ortho-substituted phenylpropiolic acids also exhibited a high reactivity (3b−g). 2-Naphthyl-substituted propiolic acid and heterocyclic thienylpropiolic acid were also suitable substrates for the transformation, affording the products 3t and 3u in 33% and 34% yield, respectively. However, alkylpropiolic acids, hex-2-ynoic acid and 3-cyclopropylpropiolic acid, failed to give the corresponding γdiketones probably due to their low reactivity (3v and 3w). Furthermore, the scope of ketones was examined. Not only primary acetone but also secondary ketones are amenable to the present transformation. Pentan-3-one provided the product 3aa in 66% yield. Cyclic ketones including cyclobutanone, cyclopentanone, and cyclohexanone also showed good efficiency, affording the γ-diketones in moderate yields (3ab−ad). However, the tertiary 2,4-dimethylpentan-3-one was inert under the standard conditions (3ae). Asymmetric ketones, butan-2-one and methyl 3-oxobutanoate, selectively provided the γ-diketones 3af and 3ag in 62% and 33% yields, respectively. This result implied that the stability of the αcarbonyl C-centered radical is the major factor that influences the regioselectivity. It was pleasant to find that ethyl acetate was compatible with this catalytic system, albeit in a low yield (3ah). When the decarboxylative oxyalkylation of phenylpropiolic acid with acetone was carried out on a gram scale (9.0 mmol), the product 3a was obtained in 72% yield. The direct C(sp3)−H functionalization of alkylnitriles is one of the most powerful methods for introducing the cyanomethyl group. We postulated that the decarboxylative oxyalkylation of alkynyl carboxylic acids might also be achieved if ketones were replaced by alkylnitriles. Gratifyingly, acetonitrile successfully underwent the decarboxylative oxyalkylation reaction with phenylpropiolic acid under the optimized conditions, furnishing the desired γ-ketonitrile 5a in 41% yield (Scheme 2). Because γ-ketonitriles are important synthetic building blocks, developing new reaction conditions for the construction of such compounds is necessary. We next optimized the reaction conditions, and the results revealed that the optimum conditions are Cu(OAc)2 (5 mol %), Mn(OAc)3·2H2O (0.5 equiv), BPO (2.0 equiv), and NaHCO3 (2.0 equiv) in a CH3CN/H2O [5/1 (v/v)] solvent at 90 °C for 6 h under an air atmosphere. Under these conditions, 5a was isolated in 73% yield (for details, see Table S9). The scope of this decarboxylative oxyalkylation of alkynyl carboxylic acids with alkylnitriles is shown in Scheme 3. Both electron-rich and -poor phenylpropiolic acids could be transferred to the γ-ketonitriles 5a−s in moderate to good yields, and a variety of functional groups including alkyl, alkoxy, amide, halides, acetyl, ester, nitrile, and nitro were well tolerated. Ortho-substituted phenylpropiolic acids also showed good efficiency. However, 2-naphthyl-substituted propiolic acid and heterocyclic thienylpropiolic acid produced the desired products 5t and 5u in only 33% and 35% yields, respectively. Alkylpropiolic acid, hex-2-ynoic acid, was inert under the standard conditions (5v). Aside from the acetonitrile, methoxyacetonitrile was a suitable substrate, although the corresponding γ-ketonitrile 5w was obtained in a low yield. Like the construction of γ-diketones, the large-scale preparation of γ-ketonitriles was also achieved under these condition. When 12.0 mmol of phenylpropiolic acid was

isolated in 16% yield (see Table S1 in the Supporting Information). In order to improve the reaction efficiency, other oxidants were tested, and benzoyl peroxide (BPO) gave the best results (see Table S1). Evaluation of a series of metal salts demonstrated that Cu(ClO4)2·6H2O was superior to others (see Table S2). Screening different ratios of acetone to H2O revealed that the mixture of acetone to H2O in a 3:1 ratio was the most efficient solvent for this decarboxylative oxyalkylation (see Table S3). The addition of base could influence the reaction efficiency. Various bases were tested, and NaHCO3 was found to be optimal (see Table S4). Interestingly, an improvement in yield was achieved when Mn(OAc)3·2H2O was employed as an additive, while the addition of other additives did not allow a further improvement (see Tables S5 and S6). Further optimization of the reactant ratio revealed that the best result was achieved when 1a, Cu(ClO4)2·6H2O, BPO, NaHCO3, and Mn(OAc)3·2H2O in a molar ratio of 1.0:0.1:3.0:3.0:0.3 were stirred in acetone/H2O [3/1 (v/v)] at 80 °C for 6 h, furnishing 3a in 76% yield (see Table S7, entry 3). With the optimal conditions in hand, the scope of the decarboxylative oxyalkylation was investigated (Scheme 2). Initially, alkynyl carboxylic acids were examined. The arylpropiolic acids with both electron-donating and -withScheme 2. Substrate Scope for the Decarboxylative Oxyalkylation of Alkynyl Carboxylic Acids with Ketonesa

Reaction conditions: 1a (0.60 mmol), Cu(ClO4)2·6H2O (10 mol %), Mn(OAc)3·2H2O (0.3 equiv), BPO (3.0 equiv), and NaHCO3 (3.0 equiv) in 6 mL of ketone/H2O [3/1 (v/v)] at 80 °C for 6 h. b Isolated yield. cThe reaction was performed in the presence of 9.0 mmol of 1a. dReaction conditions: 1a (0.60 mmol), Cu(ClO4)2· 6H2O (10 mol %), Mn(OAc)3·2H2O (0.3 equiv), BPO (3.0 equiv), and NaHCO3 (2.0 equiv) in 6 mL of ketone/H2O [3/1 (v/v)] at 100 °C for 6 h. eReaction conditions: 1a (0.60 mmol), Cu(ClO4)2·6H2O (10 mol %), Mn(OAc)3·2H2O (0.3 equiv), BPO (3.0 equiv), and NaHCO3 (3.0 equiv) in 6 mL of CH3CN/H2O [3/1 (v/v)] at 80 °C for 6 h. a

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S1). These results revealed that alkynyl copper should be involved in the process of decarboxylative oxyalkylation. When the reaction of phenylpropiolic acid with acetonitrile was performed under Ar atmosphere, 5a was obtained in 68% yield, which suggests that the oxygen atom in 5a might originate from H2O rather than O2 (see Table S9). To further confirm the oxygen donor, the isotopic-labeling experiment was carried out in the reaction between phenylpropiolic acid and acetonitrile (Scheme 4c). When H218O (with 98% abundance of 18O) was used as a cosolvent instead of normal H216O, the 18 O-labeled γ-ketonitrile 5a′ (with 87% abundance of 18O) was obtained in 63% yield. This result illustrates that water is the oxygen donor. Finally, a large primary kinetic isotope effect (KIE, 4.7) was observed in the reaction of phenylpropiolic acid with acetone/acetone-d6, thus suggest that the rate-determining step might be the C(sp3)−H bond cleavage of acetone (Scheme 4d). A primary KIE value (2.2) was also observed in the decarboxylative oxyalkylation of phenylpropiolic acid with CH3CN/CD3CN (see the SI). Based on the relevant literature7,9f,14e,15b and the aforementioned experimental results, a plausible mechanism for this decarboxylative oxyalkylation is proposed in Scheme 5.

Scheme 3. Substrate Scope for the Decarboxylative Oxyalkylation of Alkynyl Carboxylic Acids with Alkylnitrilesa

a

Reaction conditions: 1a (0.60 mmol), Cu(OAc)2 (5 mol %), Mn(OAc)3·2H2O (0.5 equiv), BPO (2.0 equiv), and NaHCO3 (2.0 equiv) in 9 mL of alkyl nitrile/H2O [5/1 (v/v)] at 90 °C for 6 h. b Isolated yield. cThe reaction was performed in the presence of 12.0 mmol of 1a. dReaction conditions: 1a (0.60 mmol), Cu(OAc)2 (5 mol %), Mn(OAc)3·2H2O (0.5 equiv), BPO (2.0 equiv), and NaHCO3 (1.0 equiv) in 9 mL of CH3CN/H2O [5/1 (v/v)] at 90 °C for 6 h.

Scheme 5. Proposed Mechanism

treated with acetonitrile, the γ-ketonitrile 5a was obtained in 65% yield. To gain mechanistic insights into this decarboxylative oxyalkylation of alkynyl carboxylic acids, we designed several control experiments. Initially, the decarboxylative oxyalkylation process was remarkably suppressed when the radical inhibitors, 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and 2,6-di-tertbutyl-4-methylphenol (BHT) were added, and TEMPO/BHTcaptured products were detected by HRMS (see the SI). These results indicate that a radical pathway is probably involved in this transformation. Furthermore, when alkynyl copper 6 was employed as reactant, γ-ketonitrile 5a was isolated in 24% yield, along with trace amounts of diyne 7 (Scheme 4a). The reaction of acetonitrile with ethynylbenzene 8 was also performed under the standard conditions, and 5a was obtained in 12% yield. Diyne 7 was not detected in this reaction (Scheme 4b). A similar yield was achieved when ethynylbenzene was added slowly to the reaction solution (see Scheme

Initially, BPO undergoes the thermal hemolytic cleavage to afford the benzoate radical. The hydrogen atom abstraction from acetone/acetonitrile by benzoate radical generates the αcarbonyl or-cyano C-centered radical. Meanwhile, the alkynyl copper 6 was produced from the decarboxylation of alkynyl carboxylic acid in the presence of copper salt. Subsequently, regioselective addition of α-carbonyl or -cyano C-centered radical to the intermediate 6 leads to vinyl radical A, which could be oxidized by BPO to generate the cation intermediate B. Compound B is trapped by H2O to form the enolate C. Finally, keto−enol tautomerism and quench with H2O of enolate C lead to the final product 3a or 5a. Mn(OAc)3·2H2O might act as a co-oxidant. In conclusion, we have demonstrated the first decarboxylative oxyalkylation of alkynyl carboxylic acids with simple ketones and alkylnitriles via direct C(sp3)−H functionalization following C−C bond formation. The mechanistic study suggested that the reaction proceeds through a radical pathway and water is involved in the transformation as an oxygen donor. The present decarboxylative oxyalkylation provides a new and general protocol for the efficient preparation of γdiketones and γ-ketonitriles from readily available alkynyl carboxylic acids.

Scheme 4. Mechanistic Studies

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DOI: 10.1021/acs.orglett.9b00520 Org. Lett. XXXX, XXX, XXX−XXX

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Wang, C.; Zhang, J.; Huang, M.; Kim, J. K.; Wu, Y. Org. Chem. Front. 2018, 5, 2496. (7) For C(sp3)−H functionalization of ketones and alkylnitriles, see: (a) Shiraishi, Y.; Tsukamoto, D.; Hirai, T. Org. Lett. 2008, 10, 3117. (b) Zhu, L.; Chen, H.; Wang, Z.; Li, C. Org. Chem. Front. 2014, 1, 1299. (c) Chu, X.; Meng, H.; Zi, Y.; Xu, X.-P.; Ji, S.-J. Chem. - Eur. J. 2014, 20, 17198. (d) Schweitzer-Chaput, B.; Demaerel, J.; Engler, H.; Klussmann, M. Angew. Chem., Int. Ed. 2014, 53, 8737. (e) Bellina, F.; Rossi, R. Chem. Rev. 2010, 110, 1082. (f) Culkin, D. A.; Hartwig, J. F. J. Am. Chem. Soc. 2002, 124, 9330. (g) You, J.; Verkade, J. G. Angew. Chem., Int. Ed. 2003, 42, 5051. (h) Liu, Y.; Yang, K.; Ge, H. Chem. Sci. 2016, 7, 2804. (i) Wu, T.; Mu, X.; Liu, G. Angew. Chem., Int. Ed. 2011, 50, 12578. (j) Liu, Y.-Y.; Yang, X.-H.; Song, R.-J.; Luo, S.; Li, J.H. Nat. Commun. 2017, 8, 14720. (8) For recent reviews on decarboxylation, see: (a) Baudoin, O. Angew. Chem., Int. Ed. 2007, 46, 1373. (b) Satoh, T.; Miura, M. Synthesis 2010, 2010, 3395. (c) Rodríguez, N.; Gooßen, L. J. Chem. Soc. Rev. 2011, 40, 5030. (d) Weaver, J. D.; Recio, A.; Grenning, A. J.; Tunge, J. A. Chem. Rev. 2011, 111, 1846. (e) Li, Z.; Jiang, Y.-Y.; Yeagley, A. A.; Bour, J. P.; Liu, L.; Chruma, J. J.; Fu, Y. Chem. - Eur. J. 2012, 18, 14527. (f) Shen, C.; Zhang, P.; Sun, Q.; Bai, S.; Hor, T. S. A.; Liu, X. Chem. Soc. Rev. 2015, 44, 291. (g) Wei, Y.; Hu, P.; Zhang, M.; Su, W. Chem. Rev. 2017, 117, 8864. (h) Park, K.; Lee, S. RSC Adv. 2013, 3, 14165. (9) (a) Moon, J.; Jeong, M.; Nam, H.; Ju, J.; Moon, J. H.; Jung, H. M.; Lee, S. Org. Lett. 2008, 10, 945. (b) Park, J.; Park, E.; Kim, A.; Park, S.-A.; Lee, Y.; Chi, K.-W.; Jung, Y. H.; Kim, I. S. J. Org. Chem. 2011, 76, 2214. (c) He, Z.; Zhang, R.; Hu, M.; Li, L.; Ni, C.; Hu, J. Chem. Sci. 2013, 4, 3478. (d) Sun, F.; Gu, Z. Org. Lett. 2015, 17, 2222. (e) Chen, S.; Wu, X.-X.; Wang, J.; Hao, X.-H.; Xia, Y.; Shen, Y.; Jing, H.; Liang, Y.-M. Org. Lett. 2016, 18, 4016. (f) Li, G.; Cao, Y.-X.; Luo, C.-G.; Su, Y.-M.; Li, Y.; Lan, Q.; Wang, X.-S. Org. Lett. 2016, 18, 4806. (g) Bhojane, J. M.; Jadhav, V. G.; Nagarkar, J. M. New J. Chem. 2017, 41, 6775. (h) Wang, D.; Zhang, L.; Luo, S. Org. Lett. 2017, 19, 4924. (10) (a) Priebbenow, D. L.; Becker, P.; Bolm, C. Org. Lett. 2013, 15, 6155. (b) Jia, W.; Jiao, N. Org. Lett. 2010, 12, 2000. (c) Yan, H.; Mao, J.; Rong, G.; Liu, D.; Zheng, Y.; He, Y. Green Chem. 2015, 17, 2723. (11) (a) Hu, J.; Zhao, N.; Yang, B.; Wang, G.; Guo, L.-N.; Liang, Y.M.; Yang, S.-D. Chem. - Eur. J. 2011, 17, 5516. (b) Li, X.; Yang, F.; Wu, Y.; Wu, Y. Org. Lett. 2014, 16, 992. (c) Zhang, P.; Zhang, L.; Gao, Y.; Xu, J.; Fang, H.; Tang, G.; Zhao, Y. Chem. Commun. 2015, 51, 7839. (d) Zhou, M.; Chen, M.; Zhou, Y.; Yang, K.; Su, J.; Du, J.; Song, Q. Org. Lett. 2015, 17, 1786. (12) Feng, Q.; Yang, K.; Song, Q. Chem. Commun. 2015, 51, 15394. (13) Zhang, L.; Hang, Z.; Liu, Z.-Q. Angew. Chem., Int. Ed. 2016, 55, 236. (14) (a) Ranjit, S.; Duan, Z.; Zhang, P.; Liu, X. Org. Lett. 2010, 12, 4134. (b) Xu, Y.; Zhao, J.; Tang, X.; Wu, W.; Jiang, H. Adv. Synth. Catal. 2014, 356, 2029. (c) Rong, G.; Mao, J.; Yan, H.; Zheng, Y.; Zhang, G. J. Org. Chem. 2015, 80, 7652. (d) Meesin, J.; Katrun, P.; Pareseecharoen, C.; Pohmakotr, M.; Reutrakul, V.; Soorukram, D.; Kuhakarn, C. J. Org. Chem. 2016, 81, 2744. (e) Yu, J.; Mao, R.; Wang, Q.; Wu, J. Org. Chem. Front. 2017, 4, 617. (f) Xiong, Y.-S.; Weng, J.; Lu, G. Adv. Synth. Catal. 2018, 360, 1611. (15) (a) Wang, S.-S.; Fu, H.; Shen, Y.; Sun, M.; Li, Y.-M. J. Org. Chem. 2016, 81, 2920. (b) Fu, H.; Shang, J.-Q.; Yang, T.; Shen, Y.; Gao, C.-Z.; Li, Y.-M. Org. Lett. 2018, 20, 489. (c) Shang, J.-Q.; Wang, S.-S.; Fu, H.; Li, Y.; Yang, T.; Li, Y.-M. Org. Chem. Front. 2018, 5, 1945.

ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.orglett.9b00520. Experimental procedures, characterization data of all products, 1H, and 13C NMR spectra (PDF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Ya-Min Li: 0000-0003-4233-5274 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This project is supported by the National Natural Science Foundation of China (Nos. 21662021 and 21871114) and the Applied Basic Research Foundation of Yunnan Province (2017FB016).

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REFERENCES

(1) (a) Furusaki, A.; Matsumoto, T.; Ogura, H.; Takayanagi, H.; Hirano, A.; Omura, S. J. Chem. Soc., Chem. Commun. 1980, 698a. (b) Enomoto, Y.; Shiomi, K.; Hayashi, M.; Masuma, R.; Kawakubo, T.; Tomosawa, K.; Iwai, Y.; Omura, S. J. Antibiot. 1996, 49, 50. (c) Peng, F.; Danishefsky, S. J. J. Am. Chem. Soc. 2012, 134, 18860. (d) Zheng, C.; Dubovyk, I.; Lazarski, K. E.; Thomson, R. J. J. Am. Chem. Soc. 2014, 136, 17750. (e) Paal, C. Ber. Dtsch. Chem. Ges. 1884, 17, 2756. (f) Knorr, L. Ber. Dtsch. Chem. Ges. 1884, 17, 2863. (g) Trost, B. M.; Doherty, G. A. J. Am. Chem. Soc. 2000, 122, 3801. (2) (a) Girgis, A. S.; Mishriky, N.; Farag, A. M.; El-Eraky, W. I.; Farag, H. Eur. J. Med. Chem. 2008, 43, 1818. (b) Provencher, B. A.; Bartelson, K. J.; Liu, Y.; Foxman, B. M.; Deng, L. Angew. Chem., Int. Ed. 2011, 50, 10565. (c) Wu, D.; O'Shea, D. F. Org. Lett. 2013, 15, 3392. (d) Frey, G.; Luu, H.-T.; Bichovski, P.; Feurer, M.; Streuff, J. Angew. Chem., Int. Ed. 2013, 52, 7131. (e) Cai, J.; Liu, L. G.; Hong, K. H.; Wang, P.; Li, L. S.; Cao, M.; Sun, C. L.; Wu, X. Q.; Zong, X.; Chen, J. Q. Bioorg. Med. Chem. 2015, 23, 657. (3) (a) Stetter, H. Angew. Chem., Int. Ed. Engl. 1976, 15, 639. (b) Bugaut, X.; Glorius, F. Chem. Soc. Rev. 2012, 41, 3511. (c) Esposti, S.; Dondi, D.; Fagnoni, M.; Albini, A. Angew. Chem., Int. Ed. 2007, 46, 2531. (d) Yasuda, M.; Oh-hata, T.; Shibata, I.; Baba, A.; Matsuda, H. J. Chem. Soc., Perkin Trans. 1 1993, 1, 859. (e) Yasuda, M.; Tsuji, S.; Shigeyoshi, Y.; Baba, A. J. Am. Chem. Soc. 2002, 124, 7440. (f) Liu, C.; Deng, Y.; Wang, J.; Yang, Y.; Tang, S.; Lei, A. Angew. Chem., Int. Ed. 2011, 50, 7337. (g) Zhang, F.; Du, P.; Chen, J.; Wang, H.; Luo, Q.; Wan, X. Org. Lett. 2014, 16, 1932. (h) Esumi, N.; Suzuki, K.; Nishimoto, Y.; Yasuda, M. Org. Lett. 2016, 18, 5704. (4) (a) Knott, E. B. J. Chem. Soc. 1947, 0, 1190. (b) Ociepa, M.; Baka, O.; Narodowiec, J.; Gryko, D. Adv. Synth. Catal. 2017, 359, 3560. (c) Zhang, S.-L.; Wang, X.-J.; Yu, Z.-L. Org. Lett. 2017, 19, 3139. (d) Zhu, Y.; Gong, J.; Wang, Y. J. Org. Chem. 2017, 82, 7428. (e) Feng, Y.-S.; Shu, Y.-J.; Cao, P.; Xu, T.; Xu, H.-J. Org. Biomol. Chem. 2017, 15, 3590. (5) (a) Mao, S.; Gao, Y.-R.; Zhang, S.-L.; Guo, D.-D.; Wang, Y.-Q. Eur. J. Org. Chem. 2015, 2015, 876. (b) Mao, S.; Zhu, X.-Q.; Gao, Y.R.; Guo, D.-D.; Wang, Y.-Q. Chem. - Eur. J. 2015, 21, 11335. (c) Xie, J.; Huang, Z.-Z. Chem. Commun. 2010, 46, 1947. (d) Lan, X.-W.; Wang, N.-X.; Zhang, W.; Wen, J.-L.; Bai, C.-B.; Xing, Y.; Li, Y.-H. Org. Lett. 2015, 17, 4460. (6) (a) Lan, X.-W.; Wang, N.-X.; Bai, C.-B.; Lan, C.-L.; Zhang, T.; Chen, S.-L.; Xing, Y. Org. Lett. 2016, 18, 5986. (b) Wu, Q.; Li, Y.; D

DOI: 10.1021/acs.orglett.9b00520 Org. Lett. XXXX, XXX, XXX−XXX