English

• Nitrogen-containing heterocycles, particularly fused-indole derivatives, are prevalent in numerous biologically significant natural products and pharmaceuticals [1-3]. As an important species of fused-indole derivatives, indolo[2, 1-a]isoquinolines with a fused tetracyclic core structure have drawn considerable attention due to their wide existence in bioactive compounds (Fig. 1) [4-12]. For example, the indolo[2, 1-a]isoquinoline derivatives C-E can act as an inhibitor of tubulin polymerization and estrogen receptor [7-11] and a melatonin antagonist [12], respectively. As a consequence, considerable efforts have been devoted to the construction of this type of polycyclic skeleton [13-21]. As for the assembly of indolo[2, 1-a]isoquinolin-6(5H)-ones, several elegant works have been reported in the past few years [22-33]. For instance, in 2015, Nevado and coworkers developed a one-pot synthesis of CF₃-, SCF₃-, Ph₂(O)P-, N₃-containing indolo[2, 1-a]isoquinolin-6(5H)-ones via a radical tandem reaction [25]. Subsequently, various functionalized indolo[2, 1-a]isoquinolin-6(5H)-ones were successfully obtained with Fe(Ⅱ)/(Ⅲ) [26,27], Pd(Ⅱ) [28,29], or Mn(Ⅲ) [30,31] as a catalyst, or Ir(Ⅲ) [32] as a photocatalyst. Despite all these achievements, the vast majority of the reported reactions are mediated by metal catalysts [24], which might limit their further synthetic applications. Therefore, development of a metal-free approach for the preparation of indolo[2, 1-a]isoquinolin-6(5H)-ones remains highly desirable.

  Figure 1

  

  Figure 1.  Selected examples of indolo[2, 1-a]isoquinolines.

  DownLoad: Full-Size Img PowerPoint

  Synthesis of sulfone-containing compounds is a hot topic in the fields of pharmaceutical chemistry and agrochemistry because of their unique anti-HIV, anticancer, and antibacterial bioactivities [33-36]. In addition, sulfones can serve as versatile building blocks in organic synthesis [37-41]. Over the past few decades, sulfonyl hydrazides have been widely utilized to install sulfonyl functional group into organic molecules [42-52]. Most importantly, they behave as a sulfonyl radical precursor to furnish sulfonyl-substituted heterocycles via sulfonyl radical-initiated addition/cyclization cascade reactions [53-62]. And a series of sulfonyl-substituted compounds, including oxindoles [53-56], isoquinoline-1, 3(2H, 4H)-diones [57,58], 3, 4-dihydroquinolin-2(1H)-ones [59], disubstituted oxazoles [60], thioflavones [56,61] and quinoline-2, 4(1H, 3H)-diones [56,62] were successively synthesized from sulfonyl hydrazides involving a sulfonyl radical intermediate. As part of our continuing interest in pursuing new methodology for heterocycle compound synthesis [63-69], herein, we report further application of readily accessible sulfonyl hydrazides to generating indolo[2, 1-a]isoquinolin-6(5H)-ones with N-substituted 2-aryl indoles as starting materials under metal-free conditions, in which a sulfonyl group was introduced simultaneously. To the best of our knowledge, synthesis of arylsulfonyl-substituted indolo[2, 1-a]isoquinolin-6(5H)-ones using sulfonyl hydrazides as free-radical precursors has never been reported.

  Our study commenced with the reaction between 2-methyl-1-(3-methyl-2-(p-tolyl)-1H-indol-1-yl)prop-2-en-1-one (1a) and tosylhydrazide (2a), using TBAI (20 mol%) as the catalyst and TBHP (70% solution in water, 3.0 equiv.) as the oxidant in CH₃CN under air at 80 ℃ for 6 h (Table 1, entry 1). Gratifyingly, the expected product, indolo[2, 1-a]isoquinolin-6(5H)-one 3aa, was obtained in 40% yield. Encouraged by the preliminary results, we next investigated other solvents such as acetone, toluene, DMF, DMAc, 1, 4-dioxane, THF, EtOH, MeOH and ⁱPrOH, revealing that MeOH was the best choice and afforded sulfone 3aa in a yield of 96% (entries 2–10). Subsequently, several other iodine sources commonly used in radical-triggered reactions were evaluated, all of which showed slightly decreased catalytic activities compared with TBAI (entries 11–14). Therefore, TBAI was chosen for further investigations. Upon testing a series of other oxidants like benzoyl peroxide (BPO), tert-butyl peroxybenzoate (TBPB), di-tert-butylperoxide (DTBP), tert-butyl peroxyacetate, and cumyl hydroperoxide (CHP), TBHP was identified as the optimal one (entries 15–19). When TBHP (in decane) was used instead of TBHP (70% solution in water), the yield of 3aa declined to 66% (entry 20). Ultimately, the control experiments showed that both TBAI and TBHP were essential for this radical cascade reaction (entries 21 and 22).

  Table 1

  

  Table 1.  Screening of reaction conditions.

  DownLoad: CSV

  With the optimized conditions established above (Table 1, entry 9), we explored the scope of arylsulfonyl hydrazides of this raection with N-methacryloyl-2-arylindole 1a (Scheme 1). Satisfyingly, a series of sulfonyl hydrazides bearing an electron-neutral group (e.g., H), an electron-donating group (e.g., Me, ^tBu, OMe), or an electron-withdrawing group (e.g., F, Cl, Br, CF₃) at the para position of the aromatic ring were well tolerated, giving the desired products 3aa-3ah in 59%–96% yields. Substrate carrying a strong electron-withdrawing group NO₂ on the benzene ring also proceeded smoothly, providing the product 3ai in a comparable yield. Additionally, meta-Cl substituted substrate was compatible with this reaction and the yield of the corresponding product 3aj was 74%. Notably, the 2-naphthalenyl (2-Np) counterpart was proven suitable for this transformation, affording indolo[2, 1-a]isoquinolin-6(5H)-one 3ak in 80% yield, whose structure was unambiguously confirmed by X-ray diffractional analysis (CCDC: 2059158).

  Scheme 1

  

  Scheme 1.  Scope of the arylsulfonyl hydrazides. Reaction conditions: 1a (0.2 mmol), 2 (2 equiv.), TBAI (20 mol%), TBHP (3 equiv.), MeOH (3 mL), air, 80 ℃, 6 h. Isolated yields.

  DownLoad: Full-Size Img PowerPoint

  Next, the scope of N-substituted 2-aryl indoles was examined for the reaction (Scheme 2). Substrates with a methoxyl, fluoro, chloro, or bromo group locating in the indole ring reacted smoothly with tosylhydrazide 2a, delivering the desired indolo[2, 1-a]isoquinolin-6(5H)-one derivatives 3ba-3ea in moderate to excellent yields (62% – 96%). And we confirmed the structure of 3da by X-ray crystallography (CCDC: 2059157). When 2-aryl indoles containing an ethyl, n-propyl, or phenyl group at the C3 position of the indole ring were employed, the corresponding products 3fa-3ha could be isolated in 61%–75% yields. As expected, 2-(4-methylphenyl)-3-phenyl-1H-indole derivatives bearing various functional groups (OMe, F, Cl and Br) in the C3-phenyl were also suitable to the reaction conditions, which could successfully be converted into sulfonated indolo[2, 1-a]isoquinolin-6(5H)-ones 3ia-3la in reasonable yields. Finally, other types of substrates, such as 1-(2-(2-fluorophenyl)-3-methyl-1H-indol-1-yl)-2-methylprop-2-en-1-one (1m) and 1-(2-(4-bromophenyl)-3-methyl-1H-indol-1-yl)-2-methylprop-2-en-1-one (1n) also underwent the reaction to provide the target products 3ma and 3na in 74% and 90% yields, respectively.

  Scheme 2

  

  Scheme 2.  Scope of the N-substituted 2-aryl indoles. Reaction conditions: 1 (0.2 mmol), 2a (2.0 equiv.), TBAI (20 mol%), TBHP (3.0 equiv.), MeOH (3.0 mL), air, 80 ℃, 6 h. Isolated yields.

  DownLoad: Full-Size Img PowerPoint

  To demonstrate the synthetic utility of this strategy, a scalability experiment was carried out under the standard conditions, in which a comparable yield (65%) of 3la was observed (Scheme 3a). Furthermore, three notable transformations of 3la were conducted (Scheme 3b). Specifically, Suzuki coupling of bromide 3la with 1-naphthylboronic acid 4 afforded the desired product 5 in an excellent yield. In addition, when treated with 1.5 equiv. of LiAlH₄ in low temperature, 3la could be easily reduced to aminal 6 in a good yield of 88%. Moreover, the synthetic utility of the sulfonated indolo[2, 1-a]isoquinolin-6(5H)-one was exemplified by halogenation of 3la with CCl₄ in the presense 3 equiv. of KOH to produce 7 in a moderate yield.

  Scheme 3

  

  Scheme 3.  Scalability experiment and representative derivatizations of 3la.

  DownLoad: Full-Size Img PowerPoint

  To confirm that the reaction was associated with a radical process, the radical quenching experiment was conducted as shown in Scheme 4. When the radical scavenger 2, 2, 6, 6-tetramethyl-1-piperidinyl-oxy (TEMPO) was added in the reaction system under the standard conditions, the cascade reaction was absolutely inhibited and the substrate 1a was recovered in 82% yield, attesting that a radical process is really involved.

  Scheme 4

  

  Scheme 4.  Control experiment.

  DownLoad: Full-Size Img PowerPoint

  Based on the control experiments and the previous reports [53,57], a plausible mechanism for the present radical cascade reaction is proposed in Scheme 5. The reaction is likely to begin with the generation of radicals t-BuO^• and t-BuOO^• from TBHP through the transformation between I⁻ and I₂. Then, sulfonyl hydrazide 2 reacts with the resulting radicals (t-BuO^• and/or t-BuOO^•) to produce the sulfonyl radical 7 by releasing N₂. Following that, addition of sulfonyl radical 7 to the C=C bond of 1a leads to the formation of carbon radical intermediate 8, which subsequently undergoes an intramolecular radical cyclization to afford intermediate 9. Finally, hydrogen abstraction of intermediate 9 occurs in the presence of TBHP, giving sulfonated indolo[2, 1-a]isoquinolin-6(5H)-one 3.

  Scheme 5

  

  Scheme 5.  Proposed mechanism.

  DownLoad: Full-Size Img PowerPoint

  In summary, we have developed an efficient TBAI/TBHP-mediated radical cascade reaction that provides a direct access to a broad range of sulfonated indolo[2, 1-a]isoquinolin-6(5H)-one derivatives from sulfonyl hydrazides with yields up to 96%. The reaction involves a sulfonyl radical intermediate generated by utilizing TBAI as the catalyst and TBHP as the oxidant. This novel protocol is characterized by metal-free conditions, easily accessible sulfonyl sources, simple operation, and broad functional group tolerance. The sulfonated indolo[2, 1-a]isoquinolin-6(5H)-one derivatives should have potential applications in organic and medicinal chemistry.

  Declaration of competing interest

  We declare that we have no financial and personal relationships with other people or organizations that can inappropriately influence our work, there is no professional or other personal interest of any nature or kind in any product, service and/or company that could be construed as influencing the position presented in the manuscript entitled.

  Acknowledgments

  We thank the State Key Basic Research Program of the People's Republic of China (No. 2018YFC0310900), National Natural Science Foundation of China (Nos. 21871018, 21801005, 21732001), Shenzhen Science and Technology Innovation Committee (Nos. KQTD20190929174023858, JCYJ20180504165454447), Industry and Information Technology Bureau of Shenzhen Municipality (No. 201806151622209330), Guangdong Science and Technology Program (No. 2017B030314002), Shenzhen-Hong Kong Institute of Brain Science-Shenzhen Fundamental Research Institutions (No. 2019SHIBS0004), and the National Ten Thousand Talent Program (the Leading Talent Tier) for the financial support. In addition, Shengxian Zhai thanks the Science and Technology Project of Henan Province (No. 202102310328), the Henan Postdoctoral Foundation and the Postdoctoral Innovation Base of Anyang Institute of Technology for financial support.

  Supplementary materials

  Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.cclet.2021.06.081.

  
  
• 1. [1]

     D.A. Horton, G.T. Bourne, M.L. Smythe, Chem. Rev.103 (2003) 893–930. doi: 10.1021/cr020033s

  2. [2]

     M. Somei, F. Yamada, Nat. Prod. Rep. 21 (2004) 278–311. doi: 10.1039/b212257j

  3. [3]

     A.J. Kochanowska-Karamyan, M.T. Hamann, Chem. Rev. 110 (2010) 4489–4497. doi: 10.1021/cr900211p

  4. [4]

     M. Lebceuf, A. Cave, A. Ranaivo, H. Moskowitz, Can. J. Chem. 67 (1989) 947–952. doi: 10.1139/v89-145

  5. [5]

     A.N.C. Lötter, R. Pathak, T.S. Sello, et al., Tetrahedron63 (2007) 2263–2274. doi: 10.1016/j.tet.2006.12.063

  6. [6]

     R. Ambros, S. von Angerer, W. Wiegrebe, Arch. Pharm. 321 (1988) 481–486. doi: 10.1002/ardp.19883210811

  7. [7]

     R. Ambros, S. Von Angerer, W. Wiegrebe, Arch. Pharm. 321 (1988) 743–747. doi: 10.1002/ardp.19883211010

  8. [8]

     R. Ambros, M.R. Schneider, S. Von Angerer, J. Med. Chem. 33 (1990) 153–160. doi: 10.1021/jm00163a026

  9. [9]

     T. Polossek, R. Ambros, S. Angerer, et al., J. Med. Chem. 35 (1992) 3537–3547. doi: 10.1021/jm00097a011

  10. [10]

      M. Goldbrunner, G. Loidl, T. Polossek, A. Mannschreck, E. von Angerer, J. Med. Chem. 40 (1997) 3524–3533. doi: 10.1021/jm970177c

  11. [11]

      R. Gastpar, M. Goldbrunner, D. Marko, E. Von Angerer, J. Med. Chem. 41 (1998) 4965–4972. doi: 10.1021/jm980228l

  12. [12]

      R. Faust, P.J. Garratt, R. Jones, et al., J. Med. Chem. 43 (2000) 1050–1061. doi: 10.1021/jm980684+

  13. [13]

      A.K. Verma, T. Kesharwani, J. Singh, V. Tandon, R.C. Larock, Angew. Chem. Int. Ed. 48 (2009) 1138–1143. doi: 10.1002/anie.200804427

  14. [14]

      A.K. Verma, R.R. Jha, R. Chaudhary, et al., J Org. Chem. 77 (2012) 8191–8205. doi: 10.1021/jo301572p

  15. [15]

      L.L. Sun, Z.Y. Liao, R.Y. Tang, C.L. Deng, X.G. Zhang, J. Org. Chem. 77 (2012) 2850–2856. doi: 10.1021/jo3000404

  16. [16]

      H. Sun, C. Wang, Y. Yang, et al., J. Org. Chem. 79 (2014) 11863–11872. doi: 10.1021/jo500807d

  17. [17]

      G. Chen, X. Zhang, R. Jia, B. Li, X. Fan, Adv. Synth. Catal. 360 (2018) 3781–3787. doi: 10.1002/adsc.201800622

  18. [18]

      S. Borthakur, B. Sarma, S. Gogoi, Org. Lett. 21 (2019) 7878–7882. doi: 10.1021/acs.orglett.9b02871

  19. [19]

      T. Zhang, Q. Zhao, W. Hao, S. Tu, B. Jiang, Chem. Asian J. 14 (2019) 1042–1049. doi: 10.1002/asia.201900050

  20. [20]

      Y. Liu, Z. Yang, R. Chauvin, et al., Org. Lett. 22 (2020) 5140–5144. doi: 10.1021/acs.orglett.0c01744

  21. [21]

      K. Sun, G. Li, Y. Li, et al., Adv. Synth. Catal. 362 (2020) 1947–1954. doi: 10.1002/adsc.202000040

  22. [22]

      G. Kraus, H. Guo, G. Kumar, et al., Synthesis (Mass)8 (2010) 1386–1393. doi: 10.1055/s-0029-1218706

  23. [23]

      F.L. Zeng, K. Sun, X.L. Chen, et al., Adv. Synth. Catal. 361 (2019) 5176–5181. doi: 10.1002/adsc.201901016

  24. [24]

      N. Fuentes, W. Kong, L. Fernández-Sánchez, E. Merino, C. Nevado, J. Am. Chem. Soc. 137 (2015) 964–973. doi: 10.1021/ja5115858

  25. [25]

      X. Su, H. Huang, W. Hong, et al., Chem. Commun. 53 (2017) 13324–13327. doi: 10.1039/C7CC08362A

  26. [26]

      J.R. Zhang, H.Y. Liu, T. Fan, Y.Y. Chen, Y.L. Xu, Adv. Synth. Catal. 362 (2020) 497–504.

  27. [27]

      X. Yang, H. Lu, X. Zhu, et al., Org. Lett. 21 (2019) 7284–7288. doi: 10.1021/acs.orglett.9b02541

  28. [28]

      H. Lu, X. Yang, L. Zhou, et al., Org. Chem. Front. 7 (2020) 2016–2021. doi: 10.1039/d0qo00492h

  29. [29]

      Y. Yuan, Y. Zheng, B. Xu, et al., ACS Catal. 10 (2020) 6676–6681. doi: 10.1021/acscatal.0c01324

  30. [30]

      S.S. Jiang, Y.T. Xiao, Y.C. Wu, et al., Org. Biomol. Chem. 18 (2020), 4843–4847. doi: 10.1039/d0ob00877j

  31. [31]

      H. Huang, Y. Li, J. Org. Chem. 82 (2017) 4449–4457. doi: 10.1021/acs.joc.7b00350

  32. [32]

      Y.L. Wei, J.Q. Chen, B. Sun, P.F. Xu, Chem. Commun. 55 (2019) 5922–5925. doi: 10.1039/c9cc02388g

  33. [33]

      T.M. Williams, T.M. Ciccarone, S.C. MacTough, et al., J. Med. Chem. 36 (1993) 1291–1294. doi: 10.1021/jm00061a022

  34. [34]

      J.B. McMahon, R.J. Gulakowski, O.S. Weislow, et al., Antimicrob. Agents Chemother. 37 (1993) 754–760. doi: 10.1128/AAC.37.4.754

  35. [35]

      M. Artico, R. Silvestri, S. Massa, et al., J. Med. Chem. 39 (1996) 522–530. doi: 10.1021/jm950568w

  36. [36]

      N. Neamati, A. Mazumder, H. Zhao, et al., Antimicrob. Agents Chemother. 41 (1997) 385–393. doi: 10.1128/aac.41.2.385

  37. [37]

      A.N.R. Alba, X. Companyo, R. Rios, Chem. Soc. Rev. 39 (2010) 2018–2033. doi: 10.1039/b911852g

  38. [38]

      C. Cassani, L. Bernardi, F. Fini, A. Ricci, Angew. Chem. Int. Ed. 48 (2009) 5694–5697. doi: 10.1002/anie.200900701

  39. [39]

      M. Nielsen, C.B. Jacobsen, N. Holub, M.W. Paixao, K.A. Jorgensen, Angew. Chem. Int. Ed. 49 (2010) 2668–2679. doi: 10.1002/anie.200906340

  40. [40]

      V. Sikervar, J.C. Fleet, P.L. Fuchs, Chem. Commun. 48 (2012) 9077–9079. doi: 10.1039/c2cc33054g

  41. [41]

      V. Sikervar, J.C. Fleet, P.L. Fuchs, J. Org. Chem. 77 (2012) 5132–5138. doi: 10.1021/jo300672a

  42. [42]

      T. Taniguchi, A. Idota, H. Ishibashi, Org. Biomol. Chem. 9 (2011) 3151–3153. doi: 10.1039/c0ob01119c

  43. [43]

      J.K. Qiu, W.J. Hao, D.C. Wang, et al., Chem. Commun. 50 (2014) 14782–14785. doi: 10.1039/C4CC06795A

  44. [44]

      R. Singh, B.K. Allam, N. Singh, et al., Org. Lett. 17 (2015) 2656–2659. doi: 10.1021/acs.orglett.5b01037

  45. [45]

      L. Tang, Y. Yang, L. Wen, X. Yang, Z. Wang, Green Chem. 18 (2016) 1224–1228. doi: 10.1039/C5GC02755A

  46. [46]

      Y. Liu, G. Zheng, Q. Zhang, Y. Li, Q. Zhang, J. Org. Chem. 82 (2017) 2269–2275. doi: 10.1021/acs.joc.6b03049

  47. [47]

      G.Y. Zhang, S.S. Lv, A. Shoberu, J.P. Zou, J. Org. Chem. 82 (2017) 9801–9807. doi: 10.1021/acs.joc.7b01121

  48. [48]

      K. Choudhuri, T.K. Achar, P. Mal, Adv. Synth. Catal. 359 (2017) 3566–3576. doi: 10.1002/adsc.201700772

  49. [49]

      Y. Yuan, Y. Yu, J. Qiao, et al., Chem. Commun. 54 (2018) 11471–11474. doi: 10.1039/c8cc06451b

  50. [50]

      Y. Yuan, Y. Cao, Y. Lin, et al., ACS Catal. 8 (2018) 10871–10875. doi: 10.1021/acscatal.8b03302

  51. [51]

      J. Wu, Y. Zhang, X. Gong, Y. Meng, C. Zhu, Org. Biomol. Chem. 17 (2019) 3507–3513. doi: 10.1039/c9ob00278b

  52. [52]

      R.J. Song, Y. Liu, Y.X. Xie, J.H. Li, Synthesis (Mass)47 (2015) 1195–1209. doi: 10.1055/s-0034-1379903

  53. [53]

      X. Li, X. Xu, P. Hu, X. Xiao, C. Zhou, J. Org. Chem. 78 (2013) 7343–7348. doi: 10.1021/jo401069d

  54. [54]

      Q. Tian, P. He, C. Kuang, Org. Biomol. Chem. 12 (2014) 6349–6353. doi: 10.1039/C4OB01231C

  55. [55]

      P.Y. Ji, M.Z. Zhang, J.W. Xu, Y.F. Liu, C.C. Guo, J. Org. Chem. 81 (2016) 5181–5189. doi: 10.1021/acs.joc.6b00773

  56. [56]

      Y.Q. Jiang, J. Li, Z.W. Feng, et al., Adv. Synth. Catal. 362 (2020) 2609–2614. doi: 10.1002/adsc.202000233

  57. [57]

      W. Yu, P. Hu, Y. Fan, et al., Org. Biomol. Chem. 13 (2015) 3308–3313. doi: 10.1039/C4OB01651C

  58. [58]

      M. Zhang, P. Xie, W. Zhao, et al., J. Org. Chem. 80 (2015) 4176–4183. doi: 10.1021/acs.joc.5b00158

  59. [59]

      Y.L. Zhu, B. Jiang, W.J. Hao, et al., Chem. Commun. 52 (2016) 1907–1910. doi: 10.1039/C5CC08895J

  60. [60]

      G.C. Senadi, B.C. Guo, W.P. Hu, J.J. Wang, Chem. Commun. 52 (2016), 11410–11413. doi: 10.1039/C6CC05138C

  61. [61]

      Z.W. Feng, J. Li, Y.Q. Jiang, et al., New J. Chem. 44 (2020) 14786–14790. doi: 10.1039/d0nj03386c

  62. [62]

      S. Wang, X. Huang, Q. Wang, et al., RSC Adv. 6 (2016) 11754–11757. doi: 10.1039/C5RA27878C

  63. [63]

      S. Zhai, S. Qiu, X. Chen, et al., ACS Catal. 8 (2018) 6645–6649. doi: 10.1021/acscatal.8b01720

  64. [64]

      S. Zhai, S. Qiu, X. Chen, et al., Chem. Commun. 54 (2018) 98–101. doi: 10.1039/C7CC08533H

  65. [65]

      H. Zhao, X. Shao, T. Wang, et al., Chem. Commun. 54 (2018) 4927–4930. doi: 10.1039/C8CC01774C

  66. [66]

      S. Qiu, S. Zhai, H. Wang, et al., Adv. Synth. Catal. 360 (2018) 3271–3276. doi: 10.1002/adsc.201800388

  67. [67]

      S. Zhai, X. Zhang, B. Cheng, et al., Chem. Commun. 56 (2020) 3085–3088. doi: 10.1039/d0cc00262c

  68. [68]

      S. Zhai, S. Qiu, L. Chen, et al., Chem. Commun. 56 (2020) 3405–3408. doi: 10.1039/d0cc00061b

  69. [69]

      H. Zhao, T. Wang, Z. Qing, H. Zhai, Chem. Commun. 56 (2020) 5524–5527. doi: 10.1039/d0cc01582b

• 

  Figure 1  Selected examples of indolo[2, 1-a]isoquinolines.

  下载: 全尺寸图片 幻灯片
  

  Scheme 1  Scope of the arylsulfonyl hydrazides. Reaction conditions: 1a (0.2 mmol), 2 (2 equiv.), TBAI (20 mol%), TBHP (3 equiv.), MeOH (3 mL), air, 80 ℃, 6 h. Isolated yields.

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Scope of the N-substituted 2-aryl indoles. Reaction conditions: 1 (0.2 mmol), 2a (2.0 equiv.), TBAI (20 mol%), TBHP (3.0 equiv.), MeOH (3.0 mL), air, 80 ℃, 6 h. Isolated yields.

  下载: 全尺寸图片 幻灯片
  

  Scheme 3  Scalability experiment and representative derivatizations of 3la.

  下载: 全尺寸图片 幻灯片
  

  Scheme 4  Control experiment.

  下载: 全尺寸图片 幻灯片
  

  Scheme 5  Proposed mechanism.

  下载: 全尺寸图片 幻灯片

  Table 1.  Screening of reaction conditions.

  下载: 导出CSV
•