English

• Enones (or α, β-unsaturated ketones) represent a fundamental scaffold in organic synthesis for a broad spectrum of synthetic transformations, such as Michael additions, Diels-Alder reactions, epoxidations (Fig. 1A) [1-12]. Notably, the enone functionality is also ubiquitous in various natural products, pharmaceuticals and biologically active molecules [13-16]. A diverse set of strategies have been developed for the efficient synthesis of enones, such as aldol or Knoevenagel condensation, Wittig olefination, dehydrogenation of ketones [17-20]. Recently, cross-coupling reactions between vinyl and acyl moieties by means of transition metal catalysis has been intensively explored that offers an efficient approach for rapid assembly of α, β-unsaturated ketones. In this context, most of these transformations relied on the cross couplings of acyl electrophiles with vinyl metallic reagents as the partners that were enabled by palladium, copper or other metal catalysis (Fig. 1B, method a) [21-26]. Alternatively, direct coupling between vinyl triflate with acyl metallic reagent as nucleophile has been achieved, as reported by Lee and co-workers (Fig. 1B, method b) [27]. In addition, the enone synthesis via cross couplings could also be realized between two electrophiles. For instance, Shu group demonstrated an elegant enone synthesis from acyl fluorides and vinyl triflates by a reductive nickel catalysis (Fig. 1B, method c) [28]. Although the metal-catalyzed coupling reactions are highly effective and synthetically useful to provide a wide range of enone derivatives, the requirement of pre-installed C–(pseudo)halide or C–metal reagents has diminished its efficiency in atom and step economy. The strategy by cross dehydrogenative coupling (CDC) [29-35] of simple aldehydes and alkenes without additional prefunctionalization thereby represents as a highly appealing approach for enone synthesis, which to our knowledge, is not achieved yet (Fig. 1B, method d).

  Figure 1

  

  Figure 1.  Importance of enones and their synthesis via cross coupling of vinyl and acyl moieties.

  DownLoad: Full-Size Img PowerPoint

  Based on our long standing interest in N-heterocyclic carbene (NHC) organocatalysis [36-52], particularly our recent focus in radical NHC catalysis [53-55], we envisioned the preparation of enones via dehydrogenative cross coupling of aldehydes and alkenes. Herein, we disclosed a highly effective carbene catalytic system that allows for straightforward assembly of simple aldehydes and alkenes to afford various enones. Mechanistically, the aldehyde C—H activation to form the ketyl radical (A) was achieved by a single-electron oxidation of the deprotonated Breslow intermediate formed by aldehyde 1 and NHC catalyst. Simultaneously, H-abstraction of the C(sp³)–H bonds by aryl radical intermediate B [56,57] in a fashion of intermolecular HAT pathway [58-64] enables an efficient activation of allylic C(sp³)–H bonds through formation of species C. Cross coupling of ketyl radical A and carbon radical C would furnish the ketone products 4′, followed by further migration of the double bond to afford the desired α, β-unsaturated ketone products 4 in high efficiency. Notably, our method represents the first example on the enone synthesis through CDC coupling of two "non-functionalized" aldehydes and alkenes as coupling partners, and offers a distinct organocatalytic pathway to the transition metal-catalyzed coupling transformations.

  Based on our hypothesis, we initiated our study on the dehydrogenative coupling reaction with benzaldehyde (1a) and cyclohexene (2a) as the model substrates (Table 1). Classical triazolium NHC catalysts A-B were first chose by employment of ortho-cyanoiodobenzene (3a) as the single-electron oxidant to test our synthetic strategy. Gratifyingly, both reactions afforded the desired coupling product 4a, albeit in relatively poor yield (entries 1 and 2). While imidazoline NHC C failed to give the product, NHC D-F featuring a mesoionic scaffold [65-69] furnished the desired product 4a in a significantly improved yield, probably owing to the strong reduction potential of the deprotonated Breslow Intermediates (BIs) derived from mesoionic carbene (MIC) (entries 4–6). Considering the pivotal role of the oxidant 3 in the radical generations, we then turned our effort to examine the effect of various aromatic iodides to achieve a more efficient catalytic system for the coupling reaction (entries 7–10). We were pleased to find that the use of a sterically hindered iodide 3e was superior to provide the coupling product 4a in 71% yield (entry 10), which probably suppressed the undesired reaction pathway triggered by the aryl radicals. Other bases, like NatBuO and Cs₂CO₃ (entries 11 and 12, see Table S2 in Supporting information for details), were also investigated, which could not give better results. Notably, the big difference between reactions with tBuOK and tBuONa might be owing to the poor solubility of tBuONa in the reaction medium (PhF), which would decrease its basicity to form the key deprotonated Breslow intermediate.

  Table 1

  

  Table 1.  Optimization of the dehydrogenative coupling reaction.^a

  DownLoad: CSV

  With the optimal reaction conditions established (Table 1, entry 10), we set out to verify the generality of the NHC-catalyzed direct dehydrogenative coupling reaction for enone synthesis (Scheme 1). Aldehyde substrates 1b-1h possessing various units on at the para position of the phenyl ring, such as Me, n-Pr, i-Pr, t-Bu, as well electron rich OMe, pH, OPh, were initially explored, leading to corresponding enone products 4b-4h in 43%−68% yields. Notably, halogen atoms (F, Cl and Br) were also compatible to deliver the products 4i-4k in 42%−69% yields, offering transferable handles for further synthetic transformations. Various substitution patterns on the aldehyde phenyl group were also investigated. For instance, F, Cl, Br, Me groups at the meta or ortho positions of aldehyde 1 afforded the corresponding enone products 4l-4r in 31%−64% yields. Moreover, the phenyl ring could also be replaced with 2-naphthalenyl (4s) and heterocyclic thienyl group (4t). Aldehydes incorporated with important moieties, such as (l)-menthol and adapalene, proceeded smoothly under the catalytic conditions to afford the enone products 4u and 4v in 68% and 38% yield, respectively, that significantly expands the synthetic utility of the developed method.

  Scheme 1

  

  Scheme 1.  Substrate scope for the coupling reactions. The reactions were performed with 1 (0.10 mmol, 1.0 equiv.), 2 (2.0 mmol, 20.0 equiv.), NHC D (20 mol%), 3e (0.3 mmol, 3.0 equiv.), and tBuOK (0.12 mmol, 1.2 equiv.) under N₂ atmosphere at 30 ℃ for 12 h; Isolated yield; Dipp = 2, 6-diisopropylphenyl.

  DownLoad: Full-Size Img PowerPoint

  We next turned to explore the scope with respect to various olefins (Scheme 1). Cyclic alkenes with five- to eight-membered rings proceeded smoothly to afford the coupling products 5a-5d with modest yields (32%−55%). Notably, the reaction with cyclooctadiene involved an isomerization of allyl radical A to B, which couples with aldehyde 1a to give the product 5d after migration of the double bond to the conjugate position. The flavor molecule, dicyclopentadiene underwent smoothly in the catalytic reaction to afford the corresponding product 5e in 45% yield. Acyclic alkenes were also feasible for the desired dehydrogenative coupling reactions. In these cases, the tetra-methylethylene afforded the coupling product 5f in 55% yield, while migration of the double bond to conjugate position of the carbonyl group was not observed, probably owing to substantial stability of the fully substituted double bond. Reaction with 2-methylbut-2-ene (2g) and 2-pentene (2h) under the optimal condition furnished the enone product 5g-5h in a relatively dropped 24% and 27% yield, respectively. We further employed an array of substituted cyclohexene (2i-2k) in this dehydrogenative coupling reaction, affording the products 5i-5k in 39%−62% yields. Intriguingly, the reactions showed distinct site selectivities depending on the different substitution patterns on the cyclohexene scaffold with a preference of site selectivity at the less hindered positions. We have never observed any corresponding coupling products at the tertiary sites, presumably owing to the notable steric hinderance between the tertiary C—H bonds and the mesityl radical species that hindered the HAT process to form the tertiary carbon radical. For instance, the 3-methyl cyclohexene (2i) gave the product 5i with C—C bond formation at the para-position of the methyl group, while 4-methyl substituted substrate 2j delivered the coupling product 5j at 6-position of the cycloalkene 2j. Additionally, an inseparable mixture of 5k (without migration of double bond) and 5k' was obtained when 1-methylcyclohexene (2k) was employed, resulted from allyl radical generation at 3 or 6 positions of 2k. Butadiene dimer 2l was also suitable to give rise to the enone product 5l in 58% yield.

  A TEMPO-trapping experiment was carried out to shed insights on the plausible reaction mechanism. Three equivalents of TEMPO were added to the catalytic conditions as illustrated in Scheme 2A. The desired dehydrogenative coupling reaction was significantly suppressed with product 4a afforded in less than 5% yield. Radical trapping adducts with aldehyde (6), and cyclohexene (7) were successfully detected that supports the proposed radical pathway. In addition, a migration of double bond from the allylic ketone 4b' was observed by subjection of 4b' under the catalytic conditions for 12 h, leading to the desired enone product 4b in 89% yield (Scheme 2B). Built upon these experiments and the substrate scope with substituted cyclohexenes, as well as our and others' previous reports [54,56,57,65], a plausible mechanism for the carbene-catalyzed enone synthesis was proposed in Scheme 2C. Firstly, deprotonated Breslow intermediate A underwent a single-electron oxidation by aromatic iodide 3e, which led to carbene-bound radical B and aryl radical C. Subsequently, hydrogen atom transfer (HAT) between species C and alkene 2 facilely occurred, giving rise to arene 8 and allyl radical D. Further radical-radical coupling with the persistent catalyst-bound radical species B would eventually afford the desired enone products 4–5 after migration of the double bond in ketone 4′−5′ and elaborated the NHC catalyst for the next catalytic cycle.

  Scheme 2

  

  Scheme 2.  Preliminary insights on the mechanism and synthetic transformations of the obtained product.

  DownLoad: Full-Size Img PowerPoint

  The catalytically generated enone products 4 can readily undergo further transformations as demonstrated in Scheme 2D. Reduction of the carbonyl moiety of 4a under CeCl₃/NaBH₄ afforded an allyl alcohol 9 with 76% yield. The double bond of the enone could also be selectively reduced to give ketone 10 in 80% yield. Treatment with TBHP/NaOH readily furnished the epoxide 11. Moreover, cyclopropanation could be prepared upon subjection with Me₃SOI/NaH to give 12 with a good yield. Reaction of the enone 4a with phenylhydrazine produced a heterocyclic compound 13 containing a pyrazole unit.

  Fascinated by the diverse biological activities of the α, β-unsaturated ketone scaffold [70], we performed preliminary studies of the antimicrobial activities with the prepared enone derivatives to develop potent antibacterial agrochemicals for crop protection (Table 2). Intriguingly, most products exhibited significant inhibitory activity against Xanthomonas oryzae pv. oryzae (Xoo), a pathogen that could lead to bacterial leaf blight (BLB) disease posing threat on rice plant [71]. Notably, 4j with a para-chloro group displayed a promising inhibition rate of 84.76% against Xoo at a concentration of 100 µg/mL, which was superior than the positive control with commercial bactericides, thiodiazole-copper (TC) and bismerthiazol (BT). Meanwhile, the obtained enone products also showed notable efficiencies on the inhibition of Xanthomonas axonopodis. pv. citri (Xac), a bacterial that would cause lesion on the surface of the plant, leading to plant necrosis [72]. In this context, compound 4i exhibited a good inhibitory activity of 69.02%, which is comparable to the inhibitory efficacy of BT (67.83%) and better than that of TC (49.77%). These findings expand the potential of our products as novel lead structures to search for potent antibacterial agents.

  Table 2

  

  Table 2.  In vitro antibacterial activity of the target compounds against Xoo and Xac.^a

  DownLoad: CSV

  In summary, we have developed an organocatalytic approach for straightforward coupling of the aldehyde and alkenes. A wide array of enone derivatives were obtained in high efficiency through the carbene-catalyzed cross dehydrogenative couplings involving a key hydrogen atom transfer (HAT) process by the in situ generated aryl radical intermediate. Notably, our method constitutes as the first example for the direct coupling of simple aldehyde and alkene without prefunctionalization for rapid assembly of enone scaffolds, that offers an alternative approach to the transition metal catalyzed coupling reactions. Ongoing studies in our laboratory include development of the carbene-catalyzed dehydrogenative coupling approach for broad implementation in C—C bond-forming coupling reactions and further explorations with the obtained enone products for potent antibacterial agents.

  Declaration of competing interest

  The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

  Acknowledgments

  We acknowledge funding supports from the National Natural Science Foundation of China (Nos. 21732002, 22061007, 22071036, and 22207022); Frontiers Science Center for Asymmetric Synthesis and Medicinal Molecules, National Natural Science Fund for Excellent Young Scientists Fund Program (Overseas), the starting grant of Guizhou University [No. (2022)47)], Department of Education, Guizhou Province [Qianjiaohe KY No. (2020)004]; The 10 Talent Plan (Shicengci) of Guizhou Province (No. [2016] 5649); Science and Technology Department of Guizhou Province (Nos. [Qiankehe-jichu-ZK[2022]zhongdian024], [2018]2802, [2019]1020, QKHJC-ZK[2022]−455); Department of Education of Guizhou Province (No. QJJ(2022)205); Program of Introducing Talents of Discipline to Universities of China (111 Program, No. D20023) at Guizhou University; Singapore National Research Foundation under its NRF Investigatorship (No. NRF-NRFI2016–06) and Competitive Research Program (No. NRF-CRP22–2019–0002); Ministry of Education, Singapore, under its MOE AcRF Tier 1 Award (Nos. RG7/20, RG70/21), MOE AcRF Tier 2 (No. MOE2019-T2–2–117), and MOE AcRF Tier 3 Award (No. MOE2018-T3–1–003); a Chair Professorship Grant, and Nanyang Technological University.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2024.109495.

  
  
• 1. [1]

     M.S. Taylor, D.N. Zalatan, A.M. Lerchner, E.N. Jacobsen, J. Am. Chem. Soc. 127 (2005) 1313–1317. doi: 10.1021/ja044999s

  2. [2]

     H. Pellissier, Adv. Synth. Catal. 357 (2015) 2745–2780. doi: 10.1002/adsc.201500512

  3. [3]

     J.S. Li, H.F. Cui, K.F. Zhang, J. Nie, J.A. Ma, Eur. J. Org. 2017 (2017) 2545–2552. doi: 10.1002/ejoc.201700249

  4. [4]

     V. Eschenbrenner-Lux, K. Kumar, H. Waldmann, Angew. Chem. Int. Ed. 53 (2014) 11146–11157. doi: 10.1002/anie.201404094

  5. [5]

     W. Lin, L. Yuan, Z. Cao, Y. Feng, L. Long, Chem. Eur. J. 15 (2009) 5096–5103. doi: 10.1002/chem.200802751

  6. [6]

     A.B. Northrup, D.W.C. MacMillan, J. Am. Chem. Soc. 124 (2002) 2458–2460. doi: 10.1021/ja017641u

  7. [7]

     Y. Wei, M. Shi, Chem. Rev. 113 (2013) 6659–6690. doi: 10.1021/cr300192h

  8. [8]

     S. Crotti, G. Belletti, N. Di Iorio, et al., RSC Adv. 8 (2018) 33451–33458. doi: 10.1039/c8ra06615a

  9. [9]

     N.J.A. Martin, B. List, J. Am. Chem. Soc. 128 (2006) 13368–13369. doi: 10.1021/ja065708d

  10. [10]

      T. Sakamoto, J. Itoh, K. Mori, T. Org. Biomol. Chem. 8 (2010) 5448–5454. doi: 10.1039/c0ob00197j

  11. [11]

      J.J. Yun, M.L. Zhi, W.X. Shi, et al., Adv. Synth. Catal. 360 (2018) 2632–2637. doi: 10.1002/adsc.201800301

  12. [12]

      M. Bougauchi, S. Watanabe, T. Arai, H. Sasai, M. Shibasaki, J. Am. Chem. Soc. 119 (1997) 2329–2330. doi: 10.1021/ja964037o

  13. [13]

      O.B. Samuelsen, O. Bergh, A. Ervik, J. Fish. Dis. 26 (2003) 339–347. doi: 10.1046/j.1365-2761.2003.00466.x

  14. [14]

      B.D. Nguyen, M.C. Roarke, J.R. Young, M. Yang, H.H. Osborn, J. Nucl. Med. Technol. 43 (2015) 239–241. doi: 10.2967/jnmt.115.161331

  15. [15]

      Z. Ye, Y. Gao, R.K. Bakshi, et al., Bioorg. Med. Chem. 10 (2000) 5–8. doi: 10.1016/S0960-894X(99)00584-3

  16. [16]

      S.L. Gaonkar, U.N. Vignesh, Res. Chem. Intermed. 43 (2017) 6043–6077. doi: 10.1007/s11164-017-2977-5

  17. [17]

      D.I. Schuster, G. Lem, N.A. Kaprinidis, Chem. Rev. 93 (1993) 3–22. doi: 10.1021/cr00017a001

  18. [18]

      H.J. Edwards, J.D. Hargrave, S.D. Penrose, C.G. Frost, Chem. Soc. Rev. 39 (2010) 2093–2105. doi: 10.1039/b919762c

  19. [19]

      G. Wittig, U. Schöllkopf, Chem. Ber. 87 (1954) 1318–1330. doi: 10.1002/cber.19540870919

  20. [20]

      D.A. Engel, G.B. Dudley, Org. Biomol. Chem. 7 (2009) 4149–4158. doi: 10.1039/b912099h

  21. [21]

      J.W. Labadie, D. Tueting, J.K. Stille, J. Org. Chem. 48 (1983) 4634–4642. doi: 10.1021/jo00172a038

  22. [22]

      K.T. Kang, S.S. Kim, J.C. Lee, Tetrahedron Lett. 32 (1991) 4341–4344. doi: 10.1016/S0040-4039(00)92165-8

  23. [23]

      M. Al-Masum, E. Ng, M.C. Wai, Tetrahedron Lett. 52 (2011) 1008–1010. doi: 10.1016/j.tetlet.2010.12.085

  24. [24]

      D. Ogawa, K. Hyodo, M. Suetsugu, et al., Tetrahedron 69 (2013) 2565–2571. doi: 10.1016/j.tet.2013.01.058

  25. [25]

      N. Jabri, A. Alexakis, J.F. Normant, Tetrahedron 42 (1986) 1369–1380. doi: 10.1016/S0040-4020(01)87356-7

  26. [26]

      M. Peña-López, M. Ayán-Varela, L.A. Sarandeses, J. Pérez Sestelo, Chem. Eur. J. 16 (2010) 9905–9909. doi: 10.1002/chem.201000726

  27. [27]

      D. Lee, T. Ryu, Y. Park, P.H. Lee, Org. Lett. 16 (2014) 1144–1147. doi: 10.1021/ol500003g

  28. [28]

      F.F. Pan, P. Guo, C.L. Li, P. Su, X.Z. Shu, Org. Lett. 21 (2019) 3701–3705. doi: 10.1021/acs.orglett.9b01164

  29. [29]

      C. Sun, G. Yin, Chin. Chem. Lett. 33 (2022) 5096–5100. doi: 10.1016/j.cclet.2022.04.026

  30. [30]

      C.J. Li, Acc. Chem. Res. 42 (2009) 335–344. doi: 10.1021/ar800164n

  31. [31]

      C. Zhang, C. Tang, N. Jiao, Chem. Soc. Rev. 41 (2012) 3464–3484. doi: 10.1039/c2cs15323h

  32. [32]

      S.A. Girard, T. Knauber, C.J. Li, Angew. Chem. Int. Ed. 126 (2014) 76–103. doi: 10.1002/ange.201304268

  33. [33]

      C. Liu, J. Yuan, M. Gao, et al., Chem. Rev. 115 (2015) 12138–12204. doi: 10.1021/cr500431s

  34. [34]

      C.Y. Huang, H. Kang, J. Li, C.J. Li, J. Org. Chem. 84 (2019) 12705–12721. doi: 10.1021/acs.joc.9b01704

  35. [35]

      A.K. Bagdi, M. Rahman, D. Bhattacherjee, et al., Green Chem. 22 (2020) 6632–6681. doi: 10.1039/d0gc02437f

  36. [36]

      V. Nair, S. Vellalath, B.P. Babu, Chem. Soc. Rev. 37 (2008) 2691–2698. doi: 10.1039/b719083m

  37. [37]

      X. Bugaut, F. Glorius, Chem. Soc. Rev. 41 (2012) 3511–3522. doi: 10.1039/c2cs15333e

  38. [38]

      A. Grossmann, D. Enders, Angew. Chem. Int. Ed. 51 (2012) 314–325. doi: 10.1002/anie.201105415

  39. [39]

      D.M. Flanigan, F. Romanov-Michailidis, N.A. White, T. Rovis, Chem. Rev. 115 (2015) 9307–9387. doi: 10.1021/acs.chemrev.5b00060

  40. [40]

      K.J.R. Murauski, A.A. Jaworski, K.A. Scheidt, Chem. Soc. Rev. 47 (2018) 1773–1782. doi: 10.1039/c7cs00386b

  41. [41]

      S. Mondal, S.R. Yetra, S. Mukherjee, A.T. Biju, Acc. Chem. Res. 52 (2019) 425–436. doi: 10.1021/acs.accounts.8b00550

  42. [42]

      X.Y. Chen, Z.H. Gao, S. Ye, Acc. Chem. Res. 53 (2020) 690–702. doi: 10.1021/acs.accounts.9b00635

  43. [43]

      A. Ghosh, A.T. Biju, Angew. Chem. Int. Ed. 60 (2021) 13712–13724. doi: 10.1002/anie.202012581

  44. [44]

      R. Song, Y. Xie, Z. Jin, Y.R. Chi, Angew. Chem. Int. Ed. 60 (2021) 26026–26037. doi: 10.1002/anie.202108630

  45. [45]

      Y. Zhang, H. Cai, X. Gan, Z. Jin, Sci. China Chem. 67 (2024) 482–511. doi: 10.1007/s11426-022-1657-0

  46. [46]

      S.W. Ragsdale, Chem. Rev. 103 (2003) 2333–2346. doi: 10.1021/cr020423e

  47. [47]

      T. Ishii, K. Nagao, H. Ohmiya, Chem. Sci. 11 (2020) 5630–5636. doi: 10.1039/d0sc01538e

  48. [48]

      L. Dai, S. Ye, Chin. Chem. Lett. 32 (2021) 660–667. doi: 10.1016/j.cclet.2020.08.027

  49. [49]

      J. Lv, Y. Nong, K. Chen, et al., Chin. Chem. Lett. 34 (2023) 10757–10762.

  50. [50]

      Q.Z. Li, R. Zeng, B. Han, J.L. Li, Chem. Eur. J. 27 (2021) 3238–3250. doi: 10.1002/chem.202004059

  51. [51]

      A.V. Bay, K.A. Scheidt, Trends Chem. 4 (2022) 277–290. doi: 10.1016/j.trechm.2022.01.003

  52. [52]

      K. Liu, M. Schwenzer, A. Studer, ACS Catal. 12 (2022) 11984–11999. doi: 10.1021/acscatal.2c03996

  53. [53]

      H. Wang, F. Su, Y. Wang, X. Wu, Y.R. Chi, Org. Chem. Front. 10 (2023) 5291–5295. doi: 10.1039/d3qo01129a

  54. [54]

      F. Su, J. Zou, X. Lv, et al., Angew. Chem. Int. Ed. 62 (2023) e202303388. doi: 10.1002/anie.202303388

  55. [55]

      F. Su, F. Lu, K. Tang, et al., Angew. Chem. Int. Ed. (2023) e202310072.

  56. [56]

      Y. Matsuki, N. Ohnishi, Y. Kakeno, et al., Nat. Commun. 12 (2021) 3848. doi: 10.1038/s41467-021-24144-2

  57. [57]

      W. Liu, A. Vianna, Z. Zhang, et al., Chem. Catal. 1 (2021) 196–206. doi: 10.1016/j.checat.2021.03.004

  58. [58]

      H.Y. Wang, X.H. Wang, B.A. Zhou, C.L. Zhang, S. Ye, Nat. Commun. 14 (2023) 4044. doi: 10.3390/s23084044

  59. [59]

      X. Wang, R. Yang, B. Zhu, et al., Nat. Commun. 14 (2023) 2951. doi: 10.1038/s41467-023-38743-8

  60. [60]

      J.L. Zhu, C.R. Schull, A.T. Tam, et al., J. Am. Chem. Soc. 145 (2023) 1535–1541. doi: 10.1021/jacs.2c12845

  61. [61]

      Q.Z. Li, R. Zeng, Y. Fan, et al., Angew. Chem. Int. Ed. 61 (2022) e202116629. doi: 10.1002/anie.202116629

  62. [62]

      Y. Man, S. Liu, B. Xu, X. Zeng, Org. Lett. 24 (2022) 944–948. doi: 10.1021/acs.orglett.1c04317

  63. [63]

      Y. Pan, Q. Li, H. Li, et al., Chem. Catal. 1 (2021) 146–161. doi: 10.1016/j.checat.2021.03.001

  64. [64]

      L. Capaldo, D. Ravelli, M. Fagnoni, Chem. Rev. 122 (2022) 1875–1924. doi: 10.1021/acs.chemrev.1c00263

  65. [65]

      Z. Zhang, S. Huang, C.Y. Li, et al., Chem. Catal. 2 (2022) 3517–3527. doi: 10.2514/1.j061307

  66. [66]

      G. Guisado-Barrios, J. Bouffard, B. Donnadieu, G. Bertrand, Angew. Chem. Int. Ed. 49 (2010) 4759–4762. doi: 10.1002/anie.201001864

  67. [67]

      G. Ung, G. Bertrand, Chem. Eur. J. 17 (2011) 8269–8272. doi: 10.1002/chem.201101130

  68. [68]

      W. Liu, L.L. Zhao, M. Melaimi, et al., Chem 5 (2019) 2484–2494. doi: 10.1016/j.chempr.2019.08.011

  69. [69]

      G. Guisado-Barrios, M. Soleilhavoup, G. Bertrand, Acc. Chem. Res. 51 (2018) 3236–3244. doi: 10.1021/acs.accounts.8b00480

  70. [70]

      M. Song, Y. Liu, T. Li, et al., Adv. Sci. 8 (2021) 2100749. doi: 10.1002/advs.202100749

  71. [71]

      A.E. Asibi, Q. Chai, J.A. Coulter, Agronomy 9 (2019) 451. doi: 10.3390/agronomy9080451

  72. [72]

      S. Ali, A. Hameed, G. Muhae-Ud-Din, et al., Agronomy 13 (2023) 1112. doi: 10.3390/agronomy13041112

• 

  Figure 1  Importance of enones and their synthesis via cross coupling of vinyl and acyl moieties.

  下载: 全尺寸图片 幻灯片
  

  Scheme 1  Substrate scope for the coupling reactions. The reactions were performed with 1 (0.10 mmol, 1.0 equiv.), 2 (2.0 mmol, 20.0 equiv.), NHC D (20 mol%), 3e (0.3 mmol, 3.0 equiv.), and tBuOK (0.12 mmol, 1.2 equiv.) under N₂ atmosphere at 30 ℃ for 12 h; Isolated yield; Dipp = 2, 6-diisopropylphenyl.

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Preliminary insights on the mechanism and synthetic transformations of the obtained product.

  下载: 全尺寸图片 幻灯片

  Table 1.  Optimization of the dehydrogenative coupling reaction.^a

  下载: 导出CSV

  Table 2.  In vitro antibacterial activity of the target compounds against Xoo and Xac.^a

  下载: 导出CSV
•