English

• 1.   Introduction

  Cyclopenta[ij]isoquinoline, a unique N-heteropolycyclic skeleton, is widely found in natural and bioactive molecules, has exhibited diverse biological activities.^[1] Among which, cyclopenta[gh]phenanthridine has attracted growing interest recently from organic chemists due to their antihuman immunodeficiency virus (HIV) activity.^[2] Although some work on the synthesis of cyclopenta[gh]phenanthridine has been reported, ^[3] some disadvantages exist with these methods, such as complicated operation, low reaction efficiency and poor substrate adaptability. Therefore, the development of alternative approach for the facile and efficient synthesis of cyclopenta[gh]phenanthridine is of great significance.

  Sulfone is also an important and essential structural scaffold in pharmaceuticals and biologically active compounds, as well as functional materials.^[4] Numerous studies on the synthesis of sulfone derivatives have been reported.^[5] The common means for preparing sulfones, including the oxidation of sulfides, ^[6] sulfonylation of arenes, ^[7] and transition metal catalyzed cross coupling, are available.^[8] Among these, sulfinate salts offer operating convenience and commercial availability for the preparation of sulfones. Based on the importance of cyclopenta[gh]phenanthridine and sulfone in various fields, efficient methods for the synthesis of sulfonated cyclopenta[gh]phenanthridine are valuable. Recently, radical cascade cyclization has emerged as a powerful strategy for the preparation of heterocycles since core structures can be built in a single operation comprising multiple bond forming steps, ^[9] thereby increasing the economy of the overall process. Inspired by recent progress on cyano-participated radical addition/cyclization for the formation of cyclic compounds, ^[10] multifunctionalized 2-alkynylnitriles were designed as radical acceptors, and we envisioned that the oxidant-mediated sulfonylation of unactivated alkynes could generate secondary alkenyl radicals, which could be coupled with late-stage radical cyclization, leading to the functionalized polycyclic heterocycles. Herein, a K₂S₂O₈ mediated cascade cyclization of 2-alkynylnitriles with sodium sulfinates was disclosed to construct sulfonated cyclopenta[gh]phenanthridines.

  2.   Results and discussion

  Initially, 3-(phenylethynyl)-[1, 1'-biphenyl]-2-carbonitrile (1a) and sodium 4-methylbenzenesulfinate (2a) were utilized as the model substrates to optimize the reaction conditions. The results are summarized in Table 1. It was found that the desired product 3aa was obtained in 41% yield when the reaction was performed in the presence of NH₄S₂O₈ as oxidant (3.5 equiv.) in CH₃CN/H₂O (V:V＝4:1) at 80 ℃ for 12 h under N₂ atmosphere (Entry 1). Encouraged by this result, the reaction conditions were further optimized by testing various oxidants. The investigation results showed that K₂S₂O₈ as an oxidant gave the best yield (83%), whereas other oxidants such as Na₂S₂O₈, t-butyl hydroperoxide (TBHP), di-tert-butyl peroxide (DTBP), t-butyl peroxybenzoate (TBPB), PhI(OAc)₂, PhI(TFA)₂ and oxone did not promote or only sluggishly promoted this reaction (Table 1, Entries 3~9). Among the solvents tested, CH₃CN/H₂O (V:V＝4:1) was found to be the best one (Table 1, Entries 10~17). In contrast, the product 3aa was isolated in low yield when the reaction was performed in the absence of H₂O or CH₃CN (Table 1, Entries 18 and 19). In addition, changing the loading of K₂S₂O₈ did not further improve the reaction either (Table 1, Entries 20 and 21). It should be noted that running the reaction at either 60 or 100 ℃ gave inferior results, which demonstrated that temperature is important (Table 1, Entries 22 and 23). The control experiment showed that no reaction occurred in the absence of K₂S₂O₈ (Table 1, Entry 24).

  Table 1

  

  Table 1.  Optimization of reaction conditions^a

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  Entry	Oxidant	Solvent (V:V)	Yiledb/%
  1	NH4S2O8	CH3CN/H2O (4:1)	41
  2	K2S2O8	CH3CN/H2O (4:1)	83
  3	Na2S2O8	CH3CN/H2O (4:1)	69
  4	TBHP	CH3CN/H2O (4:1)	Trace
  5	DTBP	CH3CN/H2O (4:1)	N.r
  6	TBPB	CH3CN/H2O (4:1)	Trace
  7	PhI(OAc)2	CH3CN/H2O (4:1)	Trace
  8	PhI(TFA)2	CH3CN/H2O (4:1)	9
  9	Oxone	CH3CN/H2O (4:1)	18
  10	K2S2O8	Actone/H2O (4:1)	36
  11	K2S2O8	DMSO/H2O (4:1)	Trace
  12	K2S2O8	DCE/H2O (4:1)	Trace
  13	K2S2O8	CH3CN/H2O (1:1)	56
  14	K2S2O8	CH3CN/H2O (3:1)	75
  15	K2S2O8	CH3CN/H2O (5:1)	69
  16	K2S2O8	CH3CN/H2O (6:1)	52
  17	K2S2O8	CH3CN/H2O (9:1)	49
  18	K2S2O8	CH3CN	39
  19	K2S2O8	H2O	Trace
  20c	K2S2O8	CH3CN/H2O (4:1)	54
  21d	K2S2O8	CH3CN/H2O (4:1)	42
  22e	K2S2O8	CH3CN/H2O (4:1)	60
  23f	K2S2O8	CH3CN/H2O (4:1)	78
  24	—	CH3CN/H2O (4:1)	N.r
  a Reaction conditions: 1a (0.2 mmol), 2a (0.5 mmol), oxidant (0.7 mmol), solvent (3 mL), 80 ℃, 12 h, N2 atmosphere. N.r.＝no reaction; b Isolated yield; c K2S2O8 (0.40 mmol); d K2S2O8 (0.80 mmol); e 60 ℃; f 100 ℃.

  With the optimized conditions in hand (Table 1, Entry 2), the scope of substrates was then studied, as shown in Table 2. The substituent effect on the benzene ring was first examined. Both electron-donating and electron-with-drawing groups on the para-position of aromatic ring produced the corresponding cyclopenta[gh]phenanthridines 3aa~3af in 49%~83% yields. When the ortho position on the benzene ring of the substrate was substituted with methyl, no desired product 3aj was obtained perhaps due to the steric effect. Next, the effect of the substitution functional groups on the arene ring of the arylalkynyl moiety was investigated. The groups, such as methyl, ethyl, tert-butyl, methoxy, fluoro, chloro, and bromo groups, were examined and gave the corresponding products 3ah~3ap in 56%~86% yields. When the arene ring of the arylalkynyl moiety was replaced by a heterocyclic ring, no desired products 3ax and 3ay were formed. Finally, the reactions of 3-(phenylethynyl)-[1, 1'-biphenyl]-2-carbonitrile (1a) with various sodium sulfinates were examined. Substituents in sodium arylsulfinates, such as p-H, p-F, p-Cl, p-Br, m-Br and m-F on the aromatic ring were compatible under the optimized conditions (3aq~3av). Moreover, when sodium cyclopropyl sulfinate were used as coupling partner, the desired product 3aw was observed in 43% yield.

  Table 2

  

  Table 2.  Scope of substrates^{a, b}

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  To shed light on the possible reaction mechanism, a radical-trapping experiment was carried out, as shown in Scheme 1. Addition of radical inhibitors, tetramethylpiperidin-1-oxyl and butylated hydroxytoluene, resulted in the inhibition of the reaction, suggesting that a radical process might be involved.

  Scheme 1

  

  Scheme 1.  Control experiments

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  On the base of the above-mentioned experiments and literature reports, ^[11] a plausible mechanism is shown in Scheme 2. First, sodium benzenesulfinate 2a was oxidized by K₂S₂O₈ to generate benzenesulfonyl radical A. Then, intermolecular addition of A to 1a offered the alkenyl radical intermediate B, which underwent rapid intramolecular cyclization to give the iminyl radical C. Subsequently, radical intermediate D could be formed by intramolecular addition of iminyl radical C to the aromatic ring. Oxidation of D produced the corresponding cation E, which underwent deprotonation to yield the desired product 3a.

  Scheme 2

  

  Scheme 2.  Proposed reaction mechanism

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  3.   Conclusions

  In conclusion, a K₂S₂O₈ initiated cascade of sulfonyl radical addition and cyclization of 2-alkynylnitriles with sodium sulfinates were developed, providing direct access to various 4-sulfonated cyclopeanta[gh]phenanthridines with C—S/C—C/C—N bond formation in one pot. This protocol is practical under the mild conditions and has good tolerance towards various functional groups. When we prepare the manuscript, Zhou's group reported similar work.^[12] Sulfurous acid was used as a free radical source, TBPB as an oxidant, and methylene chloride as a solvent in their procedure. In contrast, we use the cheaper inorganic salt K₂S₂O₈ as an oxidant, environmentally benign water as a co-solvent, which makes our reaction more economical and green.

  4.   Experimental section

  4.1   General experimental information

  ¹H NMR spectra were recorded on 400 MHz spectrometer, and ¹³C NMR spectra were recorded on 100 MHz spectrometer, Chemical shifts were recorded as residual signals relative to the solvent. High-resolution mass spectra (HRMS) were equipped with an ESI source and a TOF detector. Column chromatography was performed on silica gel (70~230 mesh ASTM) using the reported eluent. Thin-layer chromatography (TLC) was carried out on 4 cm×15 cm plates with a layer thickness of 0.2 mm (silica gel 60 F254). All reagents were purchased from commercial suppliers and used directly after purchased. All solvents were used without special precautions to squeeze out moisture.

  4.2   Experimental method

  An oven-dried Schlenk tube was equipped with a magnetic stir bar, 1 (0.2 mmol), 2 (2.5 equiv., 0.5 mmol), K₂S₂O₈ (3.5 equiv., 0.7 mmol). The flask was evacuated and backfilled with N₂ for 3 times. Then CH₃CN/H₂O (V:V＝4:1) (3 mL) was added. The tube was then sealed and the mixture was stirred for 12 h at 80 ℃ under N₂ (101 kPa). After the reaction was finished, the solvent was concentrated in vacuo and the residue was purified by chromatography on silica gel to afford the corresponding products 3.

  5-Phenyl-4-tosylcyclopenta[gh]phenanthridine (3aa): Yellow solid, 83% yield. m.p. 195~196 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.54 (dd, J＝6.2, 3.4 Hz, 1H), 8.36 (dd, J＝9.9, 7.7 Hz, 2H), 8.31 (dd, J＝6.2, 3.4 Hz, 1H), 7.87 (dd, J＝8.1, 7.3 Hz, 1H), 7.78~7.72 (m, 2H), 7.70~7.64 (m, 2H), 7.57 (d, J＝8.3 Hz, 2H), 7.53~7.47 (m, 3H), 7.11 (d, J＝8.3 Hz, 2H), 2.32 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.4, 148.3, 148.2, 144.3, 142.8, 138.5, 135.3, 132.9, 132.4, 131.2, 129.8, 129.5, 129.4, 129.0, 128.9, 128.7, 127.7, 127.6, 125.4, 124.5, 123.2, 122.9, 119.8, 21.5; HRMS (ESI) calcd for C₂₈H₂₀NO₂S [M+H]⁺ 434.1209; found 434.1211.

  8-Methyl-5-phenyl-4-tosylcyclopenta[gh]phenanthridine (3ab): Yellow solid, 49% yield. m.p. 184~186 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.41 (d, J＝8.2 Hz, 1H), 8.32 (t, J＝7.8 Hz, 2H), 8.11 (s, 1H), 7.84 (t, J＝7.7 Hz, 1H), 7.69~7.63 (m, 2H), 7.57 (d, J＝8.3 Hz, 3H), 7.53~7.46 (m, 3H), 7.11 (d, J＝8.1 Hz, 2H), 2.57 (s, 3H), 2.32 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.3, 148.5, 148.3, 144.2, 142.5, 139.2, 138.6, 135.2, 132.8, 131.9, 131.1, 130.5, 129.9, 129.4, 129.4, 129.0, 127.6, 127.6, 125.0, 123.1, 122.6, 122.2, 119.5, 21.5; HRMS (ESI) calcd for C₂₉H₂₁NO₂SNa [M+Na]⁺ 470.1185, found 470.1183.

  8-Fluoro-5-phenyl-4-tosylcyclopenta[gh]phenanthridine (3ac): Yellow solid, 65% yield. m.p. 178~180 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.53~8.45 (m, 1H), 8.31 (dd, J＝13.8, 7.7 Hz, 2H), 7.95 (dd, J＝10.0, 2.5 Hz, 1H), 7.86 (t, J＝7.7 Hz, 1H), 7.65 (dd, J＝7.6, 1.8 Hz, 2H), 7.56 (d, J＝8.3 Hz, 2H), 7.54~7.47 (m, 4H), 7.11 (d, J＝8.1 Hz, 2H), 2.32 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 162.6, 162.5 (d, J＝250.2 Hz), 149.5 (d, J＝12.4 Hz), 147.9, 144.4, 143.3, 138.3, 135.4, 133.3, 131.1, 129.6, 129.4, 128.8, 127.7, 127.6, 125.4, 124.5 (d, J＝9.4 Hz), 123.1, 121.2, 119.4, 117.7 (d, J＝24.0 Hz), 116.8 (d, J＝21.3 Hz), 21.5; ¹⁹F NMR (376 MHz, CDCl₃) δ: －110.8 (s); HRMS (ESI) calcd for C₂₈H₁₈FNO₂SNa [M+Na]⁺ 474.0934, found 474.0936.

  8-Chloro-5-phenyl-4-tosylcyclopenta[gh]phenanthridine (3ad): Yellow solid, 61% yield. m.p. 193~194 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.41 (d, J＝8.7 Hz, 1H), 8.34 (d, J＝7.1 Hz, 1H), 8.29 (dd, J＝5.2, 3.1 Hz, 2H), 7.89~7.82 (m, 1H), 7.70~7.62 (m, 3H), 7.56 (d, J＝8.3 Hz, 2H), 7.53~7.46 (m, 3H), 7.11 (d, J＝8.1 Hz, 2H), 2.32 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 162.5, 148.7, 147.9, 144.4, 143.4, 138.3, 135.4, 134.6, 133.3, 131.4, 131.1, 129.6, 129.6, 129.4, 129.1, 128.6, 127.7, 127.6, 125.7, 124.0, 123.1, 122.9, 21.5; HRMS (ESI) calcd for C₂₈H₁₈Cl-NO₂SNa [M+Na]⁺ 490.0639, found 490.0639.

  5, 8-Diphenyl-4-tosylcyclopenta[gh]phenanthridine (3ae): Yellow solid, 50% yield. m.p. 190~191 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.57 (dd, J＝6.5, 5.3 Hz, 1H), 8.36 (dd, J＝9.9, 7.7 Hz, 1H), 8.01 (dd, J＝8.4, 1.9 Hz, 1H), 7.90~7.83 (m, 1H), 7.78~7.73 (m, 1H), 7.72~7.66 (m, 1H), 7.58 (d, J＝8.3 Hz, 1H), 7.54~7.45 (m, 3H), 7.44~7.37 (m, 1H), 7.12 (d, J＝8.1 Hz, 1H), 2.33 (s, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.8, 148.7, 148.1, 144.3, 142.9, 141.7, 139.7, 138.5, 135.3, 133.0, 131.2, 130.2, 129.8, 129.6, 129.4, 129.0, 128.9, 127.9, 127.8, 127.7, 127.6, 127.3, 125.4, 123.5, 123.4, 123.3, 119.8, 21.5; HRMS (ESI) calcd for C₃₄H₂₃NO₂SNa [M+Na]⁺ 532.1342, found 532.1347.

  5-Phenyl-4-tosyl-8-(trifluoromethyl)cyclopenta[gh]phenanthridine (3af): Yellow solid, 60% yield. m.p. 213~214 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.62 (d, J＝9.3 Hz, 1H), 8.39 (dd, J＝11.5, 7.7 Hz, 1H), 7.95~7.88 (m, 1H), 7.66 (dd, J＝7.6, 1.7 Hz, 1H), 7.57 (d, J＝8.3 Hz, 1H), 7.54~7.47 (m, 1H), 7.12 (d, J＝8.2 Hz, 1H), 2.33 (s, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 162.8, 147.8, 147.4, 144.5, 143.7, 138.1, 135.4, 133.6, 130.7 (q, J＝33.0 Hz), 131.0, 130.9, 130.6, 130.2, 129.7 (q, J＝4.2 Hz), 129.5, 129.4, 128.4, 127.8, 127.6, 126.5, 124.4 (q, J＝3.4 Hz), 123.9, 123.8 (q, J＝271.3 Hz), 123.39, 120.5, 21.5; ¹⁹F NMR (376 MHz, CDCl₃) δ: －62.2 (s); HRMS (ESI) calcd for C₂₉H₁₈F₃NO₂S [M+Na]⁺ 524.0903, found 524.0901.

  5-(p-Tolyl)-4-tosylcyclopenta[gh]phenanthridine (3ah): Yellow solid, 57% yield. m.p. 197~198 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.54~8.48 (m, 1H), 8.37~8.27 (m, 3H), 7.87~7.81 (m, 1H), 7.77~7.70 (m, 2H), 7.62 (d, J＝8.2 Hz, 4H), 7.33 (d, J＝7.9 Hz, 2H), 7.13 (d, J＝8.2 Hz, 2H), 2.49 (s, 3H), 2.33 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.5, 148.5, 148.2, 144.2, 142.0, 139.8, 138.7, 135.4, 132.8, 132.3, 131.2, 129.4, 129.0, 128.8, 128.7, 128.4, 127.5, 126.9, 125.1, 124.5, 123.09, 122.9, 119.9, 21.6, 21.5; HRMS (ESI) calcd for C₂₉H₂₁NO₂SNa [M+Na]⁺ 470.1185, found 470.1182.

  5-(4-Methoxyphenyl)-4-tosylcyclopenta[gh]phenanthridine (3ai): Yellow solid, 62% yield. m.p. 190~192 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.53 (dd, J＝6.2, 3.4 Hz, 1H), 8.36~8.27 (m, 3H), 7.84 (dd, J＝8.1, 7.3 Hz, 1H), 7.78~7.72 (m, 4H), 7.61 (d, J＝8.3 Hz, 2H), 7.13 (d, J＝8.2 Hz, 2H), 7.08~7.02 (m, 2H), 3.93 (s, 3H), 2.32 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.5, 161.0, 148.2, 148.1, 144.2, 141.2, 138.7, 135.6, 133.1, 132.9, 132.3, 129.4, 129.0, 128.8, 128.7, 127.5, 125.0, 124.5, 122.9, 122.8, 122.1, 119.9, 113.3, 55.4, 21.5; HRMS (ESI) calcd for C₂₉H₂₁NO₃SNa [M+Na]⁺ 486.1134, found 486.1133.

  5-(4-Ethylphenyl)-4-tosylcyclopenta[gh]phenanthridine (3aj): Yellow solid, 60% yield. m.p. 195~196 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.55~8.48 (m, 1H), 8.32 (dt, J＝9.8, 6.4 Hz, 3H), 7.85 (t, J＝7.7 Hz, 1H), 7.78~7.70 (m, 2H), 7.61 (dd, J＝14.8, 8.2 Hz, 4H), 7.33 (d, J＝8.1 Hz, 2H), 7.10 (d, J＝8.2 Hz, 2H), 2.78 (q, J＝7.6 Hz, 2H), 2.32 (s, 3H), 1.35 (t, J＝7.6 Hz, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.5, 148.3, 148.2, 146.0, 144.1, 142.1, 138.5, 135.4, 132.9, 132.3, 131.3, 129.3, 129.0, 128.8, 128.7, 127.6, 127.2, 127.1, 125.2, 124.5, 123.0, 122.9, 119.8, 28.9, 21.5, 15.5; HRMS (ESI) calcd for C₃₀H₂₄NO₂S [M+H]⁺ 462.1522, found 462.1522.

  5-(4-(Tert-butyl)phenyl)-4-tosylcyclopenta[gh]phenanthridine (3ak): Yellow solid, 86% yield. m.p. 192~194 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.53~8.47 (m, 1H), 8.36~8.28 (m, 3H), 7.84 (d, J＝0.9 Hz, 1H), 7.76~7.69 (m, 2H), 7.64 (d, J＝8.4 Hz, 2H), 7.56 (d, J＝8.3 Hz, 2H), 7.49 (d, J＝8.4 Hz, 2H), 7.06 (d, J＝8.2 Hz, 2H), 2.30 (s, 3H), 1.42 (s, 9H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.4, 152.7, 148.2, 148.1, 144.0, 142.3, 138.3, 135.5, 132.8, 132.3, 131.0, 129.2, 129.0, 128.8, 128.6, 127.6, 126.8, 125.2, 124.7, 124.5, 123.0, 122.9, 119.8, 34.8, 31.3, 21.5; HRMS (ESI) calcd for C₃₂H₂₇NO₂SNa [M+Na]⁺ 512.1655, found 512.1654.

  5-(4-Fluorophenyl)-4-tosylcyclopenta[gh]phenanthridine (3al): Yellow solid, 80% yield. m.p. 195~197 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.51 (dd, J＝6.2, 3.3 Hz, 1H), 8.37~8.26 (m, 3H), 7.88~7.82 (m, 1H), 7.78~7.69 (m, 4H), 7.59 (d, J＝8.3 Hz, 2H), 7.20 (t, J＝8.7 Hz, 2H), 7.14 (d, J＝8.2 Hz, 2H), 2.33 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 163.7 (d, J＝250.1 Hz), 161.1, 148.1, 146.9, 144.5, 142.7, 138.4, 135.1, 133.4, 133.3, 131.4, 130.4, 129.5, 129.0 (d, J＝13.6 Hz), 128.8, 127.5, 125.7 (d, J＝3.8 Hz), 125.4, 124.5, 123.3, 122.9, 119.7, 114.9 (d, J＝21.7 Hz), 21.5; ¹⁹F NMR (376 MHz, CDCl₃) δ: －111.0 (s). HRMS (ESI) calcd for C₂₈H₁₈FNO₂SNa [M+Na]⁺ 474.0934, found 474.0939.

  5-(4-Chlorophenyl)-4-tosylcyclopenta[gh]phenanthridine (3am): Yellow solid, 73% yield. m.p. 199~200 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.51 (dd, J＝6.2, 3.3 Hz, 1H), 8.33 (dd, J＝16.4, 7.7 Hz, 2H), 8.30~8.26 (m, 1H), 7.85 (dd, J＝8.2, 7.3 Hz, 1H), 7.79~7.71 (m, 2H), 7.68~7.58 (m, 4H), 7.51~7.45 (m, 2H), 7.15 (d, J＝8.1 Hz, 2H), 2.34 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 160.9, 148.1, 146.6, 144.6, 143.0, 138.4, 135.9, 135.0, 132.9, 132.6, 132.2, 129.6, 129.0, 129.0, 128.9, 128.2, 128.0, 127.5, 125.4, 124.5, 123.4, 122.9, 119.7, 21.5; HRMS (ESI) calcd for C₂₈H₁₈ClNO₂SNa [M+Na]⁺ 490.0639, found 490.0639.

  5-(4-Bromophenyl)-4-tosylcyclopenta[gh]phenanthridine (3an): Yellow solid, 78% yield. m.p. 206~208 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.50 (dd, J＝6.2, 3.3 Hz, 1H), 8.37 (s, 1H), 8.33 (dd, J＝15.4, 7.7 Hz, 2H), 8.29~8.26 (m, 1H), 7.84 (dd, J＝8.1, 7.3 Hz, 1H), 7.77~7.71 (m, 2H), 7.66~7.55 (m, 6H), 7.16 (d, J＝8.2 Hz, 2H), 2.34 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 160.8, 148.1, 146.6, 144.6, 144.0, 138.3, 135.0, 132.9, 132.8, 132.2, 130.9, 129.6, 129.0, 129.0, 128.9, 128.7, 127.5, 125.4, 124.5, 124.3, 123.4, 122.9, 119.6, 21.5; HRMS (ESI) calcd for C₂₈H₁₈BrNO₂SNa [M+Na]⁺ 534.0134, found 534.0134.

  5-(m-Tolyl)-4-tosylcyclopenta[gh]phenanthridine (3ao): Yellow solid, 56% yield, m.p. 196~198 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.56~8.50 (m, 1H), 8.39~8.29 (m, 3H), 7.86 (dd, J＝8.2, 7.2 Hz, 1H), 7.78~7.71 (m, 2H), 7.59 (d, J＝8.3 Hz, 2H), 7.46~7.35 (m, 3H), 7.31 (d, J＝7.5 Hz, 1H), 7.12 (d, J＝8.1 Hz, 2H), 2.43 (s, 3H), 2.33 (s, 3H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.5, 148.4, 148.2, 144.2, 142.8, 138.5, 137.2, 135.3, 132.9, 132.4, 131.5, 130.3, 129.7, 129.3, 129.0, 128.8, 128.7, 128.1, 127.6, 127.6, 125.3, 124.5, 123.1, 122.9, 119.8, 21.5, 21.5; HRMS (ESI) calcd for C₂₉H₂₂NO₂S [M+H]⁺ 448.1366, found 448.1369.

  5-(3-Fluorophenyl)-4-tosylcyclopenta[gh]phenanthridine (3ap): Yellow solid, 70% yield. m.p. 194~195 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.55~8.49 (m, 1H), 8.36 (dd, J＝10.3, 7.7 Hz, 2H), 8.30 (dd, J＝6.5, 3.1 Hz, 1H), 7.87 (dd, J＝8.1, 7.3 Hz, 1H), 7.79~7.72 (m, 2H), 7.61 (d, J＝8.3 Hz, 2H), 7.47 (dd, J＝8.5, 3.4 Hz, 2H), 7.37~7.31 (m, 1H), 7.24~7.17 (m, 1H), 7.15 (d, J＝8.1 Hz, 2H), 2.34 (s, 6H); ¹³C NMR (100 MHz, CDCl₃) δ: 162.0 (d, J＝245.7 Hz), 160.9, 148.2, 146.2, 144.6, 143.5, 138.2, 134.9, 132.9, 132.3, 131.8 (d, J＝8.8 Hz), 129.5, 129.3 (d, J＝8.4 Hz), 129.1, 129.0, 128.9, 127.6, 127.1 (d, J＝2.9 Hz), 125.7, 124.5, 123.6, 122.9, 119.6, 118.1 (d, J＝22.9 Hz), 116.4 (d, J＝21.1 Hz), 21.53; ¹⁹F NMR (376 MHz, CDCl₃) δ: －113.5 (s); HRMS (ESI) calcd for C₂₈H₁₈FNO₂SNa [M+Na]⁺ 474.0934, found 474.0935.

  5-Phenyl-4-(phenylsulfonyl)cyclopenta[gh]phenanthridine (3aq): Yellow solid, 78% yield. m.p. 193~194 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.53 (dd, J＝6.1, 3.4 Hz, 1H), 8.37 (dd, J＝7.7, 3.0 Hz, 2H), 8.30 (dt, J＝7.1, 3.5 Hz, 1H), 7.87 (dd, J＝8.1, 7.3 Hz, 1H), 7.78~7.72 (m, 2H), 7.68 (td, J＝8.1, 1.5 Hz, 4H), 7.55~7.42 (m, 4H), 7.31 (t, J＝7.8 Hz, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.2, 148.6, 148.3, 142.5, 141.3, 135.2, 133.2, 132.9, 132.4, 131.1, 129.7, 129.6, 129.0, 128.9, 128.8, 128.7, 127.7, 127.5, 125.4, 124.5, 123.3, 122.9, 119.7; HRMS (ESI) calcd for C₂₇H₁₇NO₂SNa [M+Na]⁺ 442.0872, found 442.0876.

  4-((4-Fluorophenyl)sulfonyl)-5-phenylcyclopenta[gh]phenanthridine (3ar): Yellow solid, 72% yield. m.p. 182~183 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.58~8.52 (m, 1H), 8.38 (dd, J＝10.4, 7.7 Hz, 2H), 8.34~8.27 (m, 1H), 7.88 (dd, J＝8.2, 7.2 Hz, 1H), 7.80~7.73 (m, 2H), 7.70~7.60 (m, 4H), 7.56~7.46 (m, 3H), 7.00~6.90 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 165.4 (d, J＝256.9 Hz), 161.1, 148.5, 148.3, 142.5, 137.3 (d, J＝3.0 Hz), 135.1, 132.9, 132.4, 131.1, 130.4, 130.3, 129.7, 129.1, 128.9 (d, J＝10.0 Hz), 127.8, 125.4, 124.6, 123.4, 122.9, 119.7 (s), 115.9 (d, J＝22.7 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －103.8 (s); HRMS (ESI) calcd for C₂₇H₁₆FNO₂SNa [M+Na]⁺ 460.0778, found 460.0777.

  4-((4-Chlorophenyl)sulfonyl)-5-phenylcyclopenta[gh]phenanthridine (3as): Yellow solid, 74% yield. m.p. 183~185 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.60~8.53 (m, 1H), 8.40 (dd, J＝15.4, 7.7 Hz, 2H), 8.34 (dd, J＝6.3, 3.3 Hz, 1H), 7.90 (dd, J＝8.2, 7.2 Hz, 1H), 7.83~7.74 (m, 2H), 7.71~7.64 (m, 2H), 7.61~7.57 (m, 2H), 7.57~7.50 (m, 3H), 7.31~7.25 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.0, 148.8, 148.3, 142.2, 139.9, 139.7, 135.0, 132.9, 132.4, 131.1, 129.7, 129.6, 129.1, 129.9, 128.9, 127.8, 125.4, 124.6, 123.4, 122.9, 119.7; HRMS (ESI) calcd for C₂₇H₁₆ClNO₂SNa [M+Na]⁺ 476.0482, found 476.0479.

  4-((4-Bromophenyl)sulfonyl)-5-phenylcyclopenta[gh]phenanthridine (3at): Yellow solid, 65% yield. m.p. 185~187 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.56 (dd, J＝6.1, 3.4 Hz, 1H), 8.39 (dd, J＝15.9, 7.7 Hz, 2H), 8.33 (dt, J＝7.1, 3.5 Hz, 1H), 7.90 (dd, J＝8.2, 7.2 Hz, 1H), 7.82~7.76 (m, 2H), 7.68 (dt, J＝3.9, 2.3 Hz, 2H), 7.59~7.48 (m, 5H), 7.47~7.42 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.0, 148.9, 148.3, 142.1, 140.3, 135.0, 132.9, 132.4, 132.0, 131.1, 129.8, 129.6, 129.1, 129.0, 128.9, 128.5, 127.8, 125.4, 124.5, 123.4, 122.9, 119.7; HRMS (ESI) calcd for C₂₇H₁₇BrNO₂S [M+H]⁺ 498.0158, found 498.0162.

  4-((3-Bromophenyl)sulfonyl)-5-phenylcyclopenta[gh]phenanthridine (3au): Yellow solid, 46% yield. m.p. 186~188 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.58~8.53 (m, 1H), 8.39 (dd, J＝12.2, 7.7 Hz, 2H), 8.34~8.28 (m, 1H), 7.90 (dd, J＝8.1, 7.3 Hz, 1H), 7.80~7.74 (m, 2H), 7.71 (t, J＝1.7 Hz, 1H), 7.63 (dd, J＝7.7, 1.7 Hz, 2H), 7.59~7.48 (m, 5H), 7.16 (t, J＝8.0 Hz, 1H), 1.65 (s, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.0, 149.1, 148.3, 142.9, 142.0, 136.2, 135.0, 133.0, 132.4, 131.0, 130.6, 130.2, 129.9, 129.5, 129.2, 129.0, 129.0, 127.9, 126.0, 125.5, 124.6, 123.5, 123.0, 122.6, 119.6; HRMS (ESI) calcd for C₂₇H₁₆BrNO₂SNa [M+Na]⁺ 519.9977, found 519.9974.

  4-((3-Fluorophenyl)sulfonyl)-5-phenylcyclopenta[gh]phenanthridine (3av): Yellow solid, 54% yield. m.p. 184~186 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.57~8.50 (m, 1H), 8.37 (dd, J＝13.5, 7.7 Hz, 2H), 8.31 (dt, J＝7.0, 3.6 Hz, 1H), 7.88 (t, J＝7.7 Hz, 1H), 7.79~7.73 (m, 2H), 7.66 (dd, J＝7.6, 1.8 Hz, 2H), 7.57~7.48 (m, 3H), 7.46 (d, J＝7.8 Hz, 1H), 7.36~7.31 (m, 1H), 7.29 (dd, J＝8.0, 2.8 Hz, 1H), 7.14 (ddd, J＝10.1, 7.9, 2.1 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 162.0 (d, J＝251.3 Hz), 160.94 (s), 149.2, 148.3, 143.3, 143.2, 141.8, 135.0, 133.0, 132.4, 131.1, 130.5 (d, J＝7.7 Hz), 129.8, 129.6, 129.1, 129.0 (d, J＝6.7 Hz), 127.8, 125.4, 124.5, 123.5, 123.3 (d, J＝3.3 Hz), 122.9, 120.5 (d, J＝21.4 Hz), 119.6, 114.9 (d, J＝24.6 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －109.8 (s); HRMS (ESI) calcd for C₂₇H₁₆FNO₂SNa [M+Na]⁺ 460.0778, found 460.0779.

  4-(Cyclopropylsulfonyl)-5-phenylcyclopenta[gh]phenanthridine (3aw): Yellow solid, 43% yield. m.p. 227~229 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 8.59~8.52 (m, 1H), 8.42~8.33 (m, 2H), 8.21 (d, J＝7.1 Hz, 1H), 7.95~7.89 (m, 2H), 7.88~7.82 (m, 1H), 7.82~7.74 (m, 2H), 7.62~7.53 (m, 3H), 2.44 (tt, J＝8.0, 4.8 Hz, 1H), 1.32~1.16 (m, 3H), 0.95~0.82 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 161.3, 148.3, 147.2, 141.9, 135.4, 132.9, 132.4, 131.2, 130.2, 129.8, 129.1, 128.9, 128.8, 128.0, 125.3, 124.5, 123.3, 123.0, 119.6, 33.0, 5.7; HRMS (ESI) calcd for C₂₄H₁₈NO₂S [M+H]⁺ 384.1053, found 384.1050.

  Supporting Information    ¹H NMR and ¹³C NMR spectra of compounds 3aa~3aw. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn.

  
  Dedicated to the 40th anniversary of Chinese Journal of Organic Chemistry.
  
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• 

  Scheme 1  Control experiments

  下载: 全尺寸图片 幻灯片
  

  Scheme 2  Proposed reaction mechanism

  下载: 全尺寸图片 幻灯片

  Table 1.  Optimization of reaction conditions^a

  Entry	Oxidant	Solvent (V:V)	Yiledb/%
  1	NH4S2O8	CH3CN/H2O (4:1)	41
  2	K2S2O8	CH3CN/H2O (4:1)	83
  3	Na2S2O8	CH3CN/H2O (4:1)	69
  4	TBHP	CH3CN/H2O (4:1)	Trace
  5	DTBP	CH3CN/H2O (4:1)	N.r
  6	TBPB	CH3CN/H2O (4:1)	Trace
  7	PhI(OAc)2	CH3CN/H2O (4:1)	Trace
  8	PhI(TFA)2	CH3CN/H2O (4:1)	9
  9	Oxone	CH3CN/H2O (4:1)	18
  10	K2S2O8	Actone/H2O (4:1)	36
  11	K2S2O8	DMSO/H2O (4:1)	Trace
  12	K2S2O8	DCE/H2O (4:1)	Trace
  13	K2S2O8	CH3CN/H2O (1:1)	56
  14	K2S2O8	CH3CN/H2O (3:1)	75
  15	K2S2O8	CH3CN/H2O (5:1)	69
  16	K2S2O8	CH3CN/H2O (6:1)	52
  17	K2S2O8	CH3CN/H2O (9:1)	49
  18	K2S2O8	CH3CN	39
  19	K2S2O8	H2O	Trace
  20c	K2S2O8	CH3CN/H2O (4:1)	54
  21d	K2S2O8	CH3CN/H2O (4:1)	42
  22e	K2S2O8	CH3CN/H2O (4:1)	60
  23f	K2S2O8	CH3CN/H2O (4:1)	78
  24	—	CH3CN/H2O (4:1)	N.r
  a Reaction conditions: 1a (0.2 mmol), 2a (0.5 mmol), oxidant (0.7 mmol), solvent (3 mL), 80 ℃, 12 h, N2 atmosphere. N.r.＝no reaction; b Isolated yield; c K2S2O8 (0.40 mmol); d K2S2O8 (0.80 mmol); e 60 ℃; f 100 ℃.

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  Table 2.  Scope of substrates^{a, b}

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•