1 Introduction
Hypervalent iodine reagents have gained significant interest due to their exceptional reactivity, non-toxic nature, and eco-friendly properties.[1] Among them, diaryliodonium salts (Ar2IX) as efficient arylating reagents exhibit powerful reactivity in arylation reactions. Structurally, Ar2IX can be primarily classified into acyclic and cyclic diaryliodonium salts (Scheme 1a).[2] Over the past few decades, synthetic approaches have been developed for these compounds since Olofsson simplified the one-pot synthetic procedure.[1f] Generally, diaryliodonium salts are involved in two main types of arylations: one entails the mono-activation of the C—I bond of diaryliodonium salts for direct arylations, and the other involves the synergic activation of both the C—I bond and the ortho-C—H/FG bond of Ar2IX for cascade or cyclization reactions.[1,3] In contrast to the waste residues generated from the acyclic Ar2IX arylation reaction, cyclic diaryliodonium salts which feature rigid geometry by linking the two aromatic rings, align with the requirements of green chemistry rules and have made significant progress in the recent years.[4-5]
Owing to their inherent structure and highly electron- deficient property, cyclic aryliodonium salts were frequently employed in the construction of polycyclic scaffolds. In recent years, a significant progress has been made in synthetic methodology and applications in bioactive agents and halogen-catalysts with cyclic Ar2IX.[5] Cyclic aryliodonium salts offer the advantage of reacting with various nucleophiles in a one-pot process under the suitable conditions with an excellent atom-economy.
As a consequence, the synthesis of cyclic aryliodonium salts is highly desirable. Currently, Most studies focus on central five-membered or carbon-bridged six-membered Ar2IX. However, the preparation of heteroatom-bridged cyclic Ar2IX is relatively limited. In 1965, Beringer et al.[6] reported the first heteroatom-bridged six-membered cyclic Ar2IX from o-iododiphenyl ether or o-iododiphenylamine in two steps (Scheme 1, b-1). The research groups of Wen[7a] and Huber[7b] also reported the synthesis of oxygen-bridged cyclic diaryliodonium salts. In 2022, Nachtsheim[8] reported an elegant one-pot method for synthesizing nitrogen- or oxygen-containing cyclic Ar2IX, avoiding the separation of intermediates (Scheme 1, b-2). Subsequently, Olofssonv et al.[9] described the synthesis of oxygen-bridged cyclic diaryliodonium salts from ortho-iodo- aryl ethers and the inexpensive oxidant mCPBA, in which the substrates bear strong electron-withdrawing groups (Scheme 1, b-3). Recently, our group[10] disclosed the synthesis of ortho-iododiphenyl ethers and ortho-iododiphenyl sulfonamides through intramolecular aryl migrations with functionalized diaryliodonium salts. We herein synthesized the heteroatom-bridged six-membered cyclic diaryliodo- nium salts using a three-step one-pot procedure (Scheme 1c).
2 Results and discussion
With a series of ortho-OTf substituted diaryliodonium salts in hand, oxygen-bridged six-membered cyclic diaryliodonium salts were successfully synthesized. The generality of the substrates was examined as shown in Table 1. The results exhibited that the aryl groups (Ar2) in the substrates including electron-withdrawing group or electron- donating group were well tolerated in the reaction, the cyclic Ar2IX of 2aa~2ah were obtained in 56%~80% yields. Among them, Ar2 at the para-position are fluorine (2ae), chlorine (2af), and bromine (2ag), the desired pro-ducts were obtained in moderate yields of 63%~70%, indicating that the electron-withdrawing property was preferable for this reaction. The methyl substituent of Ar2 at different positions gave the similar yields (2ab, 2ac, 2ad) ranging from 60% to 71%. It indicated that electronic or steric effects from substituents close to the bridge atoms may affect the oxidation of iodine. An unsuccessful example of 2ai was attributed to the poor solubility of the starting materials. Pleasingly, heterocycles of coumarin were employed in this procedure, producing the corresponding products 2aj and 2ak in 59% and 29% yields, respectively. Next, the generality of substituents and their substituted positions on the aryl (Ar1) of diaryliodonium salts was examined. The results showed that substrates with electron-withdrawing groups had slightly higher yields than those with electron-donating groups. Generally, the substrates with electron-withdrawing groups including ester, and chlorine, gave favorable yields (2ga, 80% yield; 2ia, 87% yield). In contrast, 2ha bearing trifluoromethyl substituent was obtained in 54% yield. For the halogen substituents, the efficiency depended on the substituted positions (2ea, 61% yield vs 2ga, 80% yield).
Table 1 Substrate expansion of oxygen-bridged six-membered cyclic diaryliodonium saltsa,b |
 |
a Reaction conditions: (1) Diaryliodonium salts 1 (0.5 mmol, 1 equiv.), Cs2CO3 (0.55 mmol, 1.1 equiv.) in 5 mL of anhydrous MeCN, r.t., 12 h; (2) Selectfluor (2 mmol, 4 equiv.), AcOH (0.3 mL), r.t., 24 h; (3) TfOH (2 mmol, 4 equiv.) at 0 ℃, then at 80 ℃ for 2 h. b Isolated yield after column chromatography. |
We[10b] subsequently investigated ortho-N-acetyl sulfonamides containing diaryliodonium salts in the protocol based on the previous work in our group (Table 2). As a result, the reaction conditions were modified to achieve nitrogen-bridged cyclic diaryliodonium salts with yields ranging from 48% to 90%. The results suggested that the substituents of sulfonamides have a slight effect on the reaction, regardless of steric hindrance. As such, 4aa~4ag were obtained in 58%~90% yields. With R of ethyl group as an optimal substituent, the aryl structure of the diaryliodonium salts was considered to expand the reaction scope. As shown in Table 2, When Ar2 bearing substituents of methyl (4ca), and fluorine (4da), the yields were obtained in 48%~50%. However, neither 4ea nor 4fa was not observed, possibly due to their instability in the reaction conditions. For the aryl group of Ar1, it was found that neither electron-withdrawing nor electron-donating groups were effective due to the failure of the cyclization process. One example of para-chloro-substituted six-membered cyclic diaryliodonium salt of 4ba was achieved in a yield of 52%.
Table 2 Substrate expansion of N-bridged heterocyclic diaryliodonium saltsa,b |
 |
a Reaction conditions: (1) Diaryliodonium salts 3 (0.5 mmol, 1 equiv.), DMAP (0.5 mmol, 1 equiv.) in 5 mL of anhydrous MeCN, 80 ℃, 12 h; (2) Selectfluor (2 mmol, 4 equiv.), AcOH (0.3 mL), r.t., 24 h; (3) TfOH (2 mmol, 4 equiv.) at 0 ℃, then at 80 ℃ for 2 h, b Isolated yield after column chromatography. |
The formation of six-membered cyclic diaryliodonium salts proceeds through three consecutive stages: (1) an intramolecular aryl migration, (2) oxidation of the iodine center, and (3) acid-mediated cyclization. Initially, diaryliodonium salts 1 and 3 undergo an intramolecular aryl migration under basic conditions, giving ortho-iododiaryl ethers or ortho-iododiarylamines 5a. In the next step, oxidation of the iodine center to the trivalent state 5b (L=OAc) is achieved using the oxidant Selectfluor in the presence of AcOH. Finally, trifluoromethanesulfonic acid (TfOH) simultaneously activates the C—H bond and promotes cyclization, leading to the formation of cyclic diaryliodonium salts 2 and 4.
Furthermore, The experiments were carried out with further transformation of 2aj and 2ak in intramolecular coupling reactions. As shown in Scheme 2, the π-expanded coumarin derivatives of 2aj' and 2ak' were obtained in 80% and 74% yields in the presence of palladium catalysts, and their UV absorption with the heterocyclic diaryliodonium salts containing coumarin skeleton were measured (Figure 1). All data were recorded at a concentration of 1×105 mol/L in MeCN. The maximum absorption peaks of 2aj and 2ak are 317 and 319 nm, indicating that the introduction of coumarin substituents can significantly affect the photochemical properties of the compounds. The maximum UV absorption peak of 2aj' with coumarin unit shifted significantly in comparison of 2aj, reaching 325 nm in wavelength. The maximum UV absorption peak of 2ak' reached 330 nm in wavelength. According to our group’s previous work,[10d] derivatives 2ak' and 2aj' show increased absorption and fluorescence intensities over the parent coumarin molecule. Therefore, the coumarin-based cyclic diaryliodonium salts might find their potential applications in photo-polymerization chemistry.
Scheme 2 Further transformations of coumarin-based cyclic diaryliodonium saltsReaction conditions: diaryliodonium salts 2aj/2ak (0.5 mmol, 1 equiv.), Pd/C (0.0025 mmol, 0.05 equiv.) and NaOAc (1.5 mmol, 3 equiv.) in 5 mL of DMA, 140 ℃, 24 h. Isolated yield after column chromatography. |
3 Conclusion
In summary, an approach was developed in synthesizing heteroatom-bridged cyclic diaryliodonium salts from ortho-functionalized diaryliodonium salts through a three- step one-pot method. This study expanded the further utilization of intramolecular aryl migration in our previous study. Furthermore, the coumarin-containing cyclic diaryl- iodonium salts were prepared in this procedure by in- corporation of coumarin skeleton. The photochemical properties of heteroatom-bridged cyclic diaryliodonium salts were evaluated by using UV-Visible absorption measurements, demonstrating their potential applications in photochemistry. Our laboratory is currently investi- gating the unique properties and applications of these aryliodoniums in photochemistry.
4 Experimental Section
4.1 General methods
1H NMR and 13C NMR spectra were recorded on a Bruker AVANCE 400 spectrometer, operating at 400 MHz for 1H NMR and 100 MHz for 13C NMR. Mass spectra were in general recorded on a Waters LCT Premier XE spectrometer. Column chromatography was performed with a silica gel (200~300 mesh ASTM). All solvents were dried and/or distilled by standard methods. All reagents were purchased from commercial sources and used without further purification. Reactions were monitored by TLC (detection with UV light).
4.2 Synthesis and characterization of oxygenated hexa-membered heterocyclic diaryliodonium salts
To an oven-dried Schlenk tube was added iodonium salts (0.5 mmol, 1 equiv.) and Cs2CO3 (0.55 mmol, 1.1 equiv.). The tube was degassed with argon for three times. Acetonitrile (5 mL) was added via syringe, and the mixture was stirred at room temperature for 12 h. After TLC indicated that the diaryliodonium salts were completely consumed, Selectfluor (2.0 mmol, 4 equiv.) was subsequently added, followed by the addition of 0.5 mL of acetic acid. This mixture was stirred at room temperature for 24 h. After the reaction was detected by TLC, the reaction mixture was treated with trifluoromethanesulfonic acid (2.0 mmol, 4 equiv.) under ice-bath cooling and stirred for 10 minutes. The reaction temperature was adjusted to 80 ℃ and maintained for 2 h. The mixture was washed with water (30 mL) and extracted with DCM (15 mL) for three times. Then the solvent was evaporated under vacuum. The crude products were purified using flash column chromatography [eluent: V(di- chloromethane)∶V(methanol)=20∶1] on silica gel to afford the desired product.
5H-5λ3-Dibenzo[b,e][1,4]iodaoxin-5-yl trifluorometha- nesulfonate (2aa): 80% yield (178 mg), white solid, column chromatography [V(dichloromethane)∶V(metha- nol)=20∶1]. m.p. 181~183 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.07 (d, J=8.1 Hz, 2H), 7.76~7.63 (m, 4H), 7.55~7.37 (m, 2H); 13C NMR (101 MHz, DMSO-d6) δ: 153.5, 133.5, 133.5, 128.2, 121.6, 120.7 (q, JC-F=324.2 Hz), 102.4; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C12H8IO [MOTf]＋ 294.9614, found 294.9611.
1-Methyl-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluoromethanesulfonate (2ab): 60% yield (136 mg), yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 177~179 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.04 (dd, J=8.2, 1.5 Hz, 1H), 7.84 (d, J=8.3 Hz, 1H), 7.78 (dd, J=8.2, 1.5 Hz, 1H), 7.67 (td, J=7.7, 1.5 Hz, 1H), 7.54 (d, J=8.5 Hz, 1H), 7.49~7.40 (m, 1H), 7.32 (t, J=7.8 Hz, 1H), 2.51 (s, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 153.6, 151.7, 134.4, 133.6, 133.5, 131.5, 131.0, 128.2, 127.6, 122.0, 120.7 (q, JC-F=320.1 Hz), 103.5, 103.3, 16.0; 19F NMR (376 MHz, DMSO-d6) δ: 77.77; HRMS (ESI) calcd for C13H10IO [MOTf]＋ 308.9771, found 308.9766.
2-Methyl-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ac): 71% yield (162 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 180~182 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.02 (d, J=8.1 Hz, 1H), 7.88 (d, J=8.2 Hz, 1H), 7.66 (d, J=3.9 Hz, 2H), 7.53 (d, J=1.2 Hz, 1H), 7.46~7.40 (m, 1H), 7.26 (dd, J=8.3, 1.3 Hz, 1H), 2.39 (s, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 153.6, 153.4, 144.3, 133.5, 133.4, 132.9, 128.9, 128.0, 121.9, 121.6, 119.6 (q, JC-F=317.1 Hz), 102.6, 98.6, 20.6; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C13H10IO [MOTf]＋ 308.9771, found 308.9765.
3-Methyl-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ad): 70% yield (159 mg), yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 175~177 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.03 (dd, J=8.1, 1.3 Hz, 1H), 7.82 (dd, J=2.1, 0.8 Hz, 1H), 7.72~7.64 (m, 2H), 7.59 (d, J=8.3 Hz, 1H), 7.51~7.39 (m, 2H), 2.37 (s, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 153.7, 151.4, 138.0, 133.9, 133.5, 133.5, 133.1, 128.0, 121.6, 121.1, 120.7 (q, JC-F=320.1 Hz), 102.7, 102.3, 20.2; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C13H10IO [MOTf]＋ 308.9771, found 308.9766.
3-Fluoro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ae): 70% yield (162 mg), white solid, column chromatography [V(dichloromethane)∶V(me- thanol)=20∶1]. m.p. 170~172 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.04 (dd, J=8.2, 1.3 Hz, 1H), 7.88 (dd, J=7.5, 3.0 Hz, 1H), 7.78 (dd, J=9.0, 4.6 Hz, 1H), 7.74~7.66 (m, 2H), 7.63~7.56 (m, 1H), 7.50~7.43 (m, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 159.3 (d, JC-F=249.5 Hz), 153.6, 150.5 (d, JC-F=2.0 Hz), 133.7, 133.5, 128.3, 122.7 (d, JC-F=9.1 Hz), 121.7, 120.5 (d, JC-F=23.2 Hz), 120.1 (d, JC-F=27.3 Hz), 118.2 (q, JC-F=186.9 Hz), 103.1 (d, JC-F=9.1 Hz), 102.9; 19F NMR (376 MHz, DMSO-d6) δ: 77.76(s), 113.58 (s); HRMS (ESI) calcd for C12H7- FIO [MOTf]＋ 312.9520, found 312.9512.
3-Chloro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2af): 63% yield (150 mg), white solid, Column chromatography [V(dichloromethane)∶V(me- thanol)=20∶1]. m.p. 188~190 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.08~8.01 (m, 2H), 7.80~7.67 (m, 4H), 7.47 (td, J=7.6, 6.8, 2.1 Hz, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 153.3, 152.7, 133.6, 133.5, 133.3, 132.5, 131.0, 128.4, 122.8, 121.7, 120.7 (q, JC-F=324.2 Hz), 103.3, 102.4; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C12H7ClIO [MOTf]＋ 328.9225, found 328.9218.
3-Bromo-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ag): 66% yield (172 mg), white solid, column chromatography [V(dichloromethane)∶V(me- thanol)=20∶1]. m.p. 193~195 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.06 (d, J=7.9 Hz, 1H), 7.90 (dd, J=7.5, 3.0 Hz, 1H), 7.78 (dd, J=9.0, 4.6 Hz, 1H), 7.74~7.67 (m, 2H), 7.60 (td, J=8.6, 3.0 Hz, 1H), 7.48 (td, J=6.4, 3.4 Hz, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 158.0, 153.7, 150.5, 150.4, 133.6, 133.5, 128.3, 122.6, 121.7, 121.3, (q, JC-F=275.3 Hz)120.6, 103.4, 103.1; 19F NMR (376 MHz, DMSO-d6) δ: 77.77; HRMS (ESI) calcd for C12H7BrIO [MOTf]＋ 372.8719, found 372.8714.
2-Chloro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ah): 56% yield (134 mg), yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 170~172 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.07~8.00 (m, 2H), 7.90 (d, J=2.3 Hz, 1H), 7.69 (d, J=3.9 Hz, 2H), 7.56 (dd, J=8.7, 2.3 Hz, 1H), 7.46 (dt, J=8.8, 4.6 Hz, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 154.4, 153.2, 137.7, 134.6, 133.6, 133.5, 128.5, 128.1, 121.8, 121.8, 120.7 (q, JC-F=323.2 Hz), 102.4, 101.1; 19F NMR (376 MHz, DMSO-d6) δ: 77.77; HRMS (ESI) calcd for C12H7ClIO [MOTf]＋ 328.9225, found 328.9221.
3-Methyl-2-oxo-11λ3-benzo[b]chromeno[6,7-e][1,4]io-daoxin-11(2H)-yl trifluoromethanesulfonate (2aj): 59% yield (59 mg), white solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 168~170 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.06 (d, J=6.8 Hz, 1H), 7.96~7.86 (m, 2H), 7.78 (dd, J=8.1, 1.5 Hz, 1H), 7.76~7.67 (m, 2H), 7.48 (ddd, J=8.5, 7.3, 1.6 Hz, 1H), 2.21 (s, 2H); 13C NMR (101 MHz, DMSO-d6) δ: 160.4, 154.1, 151.7, 150.6, 139.1, 136.3, 135.7, 133.6, 128.4, 127.4, 122.6, 121.6, 121.7 (q, JC-F=324.2 Hz), 121.1, 119.8, 105.3, 16.8; 19F NMR (376 MHz, DMSO-d6) δ: 77.73; HRMS (ESI) calcd for C16H10IO3 [MOTf]＋376.9669, found 376.9656.
3-(2-Oxo-2H-chromen-3-yl)-5H-5λ3-dibenzo[b,e][1,4]-iodaoxin-5-yl trifluoromethanesulfonate (2ak): 29% yield (84 mg), yellow solid, column chromatography [V(dich- loromethane)∶V(methanol)=20∶1]. m.p. 196~198 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.50 (d, J=2.1 Hz, 1H), 8.32 (s, 1H), 8.14 (dd, J=8.1, 1.4 Hz, 1H), 7.98 (dd, J=8.6, 2.2 Hz, 1H), 7.83~7.74 (m, 2H), 7.73~7.62 (m, 2H), 7.51~7.37 (m, 4H); 13C NMR (101 MHz, DMSO-d6) δ: 171.7, 159.6, 153.5, 153.4, 153.2, 141.7, 134.3, 133.6, 133.4, 133.2, 132.5, 129.0, 128.3, 124.9, 124.4, 121.7, 121.3, 120.7 (q, JC-F=324.2 Hz) 119.3, 116.1, 102.4, 102.3; 19F NMR (376 MHz, DMSO-d6) δ: 77.73; HRMS (ESI) calcd for C21H12IO3 [MOTf]＋ 438.9826, found 438.9808.
2-Methyl-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ba): 81% yield (185 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 181~183 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.04 (d, J=8.0 Hz, 1H), 7.90 (d, J=8.3 Hz, 1H), 7.71~7.66 (m, 2H), 7.59~7.55 (m, 1H), 7.45 (ddd, J=8.5, 5.6, 3.2 Hz, 1H), 7.29 (dd, J=8.3, 1.9 Hz, 1H), 2.41 (s, 3H); 13C NMR (151 MHz, DMSO-d6) δ: 153.6, 153.4, 144.3, 133.5, 133.4, 132.9, 128.9, 128.0, 121.9, 121.6, 119.6 (q, JC-F=317.1 Hz), 102.6, 98.6, 20.6; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C13H10IO [MOTf]＋ 308.9771, found 308.9765.
3-Methyl-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ca): 70% yield (161 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 173~175 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.03 (dd, J=8.1, 1.3 Hz, 1H), 7.82 (dd, J=2.1, 0.8 Hz, 1H), 7.72~7.64 (m, 2H), 7.59 (d, J=8.3 Hz, 1H), 7.51~7.39 (m, 2H), 2.37 (s, 3H); 19F NMR (376 MHz, DMSO-d6) δ: 77.77; HRMS (ESI) calcd for C13H10IO [MOTf]＋ 308.9771, found 308.9764.
3-Fluoro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2da): 54% yield (121 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 171~173 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.04 (dd, J=8.1, 1.3 Hz, 1H), 7.88 (dd, J=7.4, 3.0 Hz, 1H), 7.77 (dd, J=9.0, 4.5 Hz, 1H), 7.70 (qd, J=8.2, 1.8 Hz, 2H), 7.59 (td, J=8.5, 3.0 Hz, 1H), 7.47 (ddd, J=8.5, 6.7, 2.2 Hz, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 159.3 (d, JC-F=249.5 Hz), 153.6, 150.5 (d, JC-F=2.0 Hz), 133.7, 133.5, 128.3, 122.7 (d, JC-F=9.1 Hz), 121.7, 120.5 (d, JC-F=23.2 Hz), 120.1 (d, JC-F=27.3 Hz), 118.2 (q, JC-F=186.9 Hz), 103.1 (d, JC-F=9.1 Hz), 102.9; 19F NMR (376 MHz, DMSO-d6) δ: 77.76 (s), 113.57 (s); HRMS (ESI) calcd for C12H7FIO [MOTf]＋ 312.9520, found 312.9512.
3-Chloro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ea): 61% yield (145 mg), white solid, column chromatography [V(dichloromethane)∶V(me- thanol)=20∶1]. m.p. 188~190 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.07~8.02 (m, 2H), 7.80~7.74 (m, 2H), 7.72~7.69 (m, 2H), 7.47 (ddd, J=8.5, 6.8, 2.1 Hz, 1H); 19F NMR (376 MHz, DMSO-d6) δ: 77.74; 13C NMR (101 MHz, DMSO-d6) δ: 153.3, 152.7, 133.6, 133.5, 133.3, 132.5, 131.0, 128.4, 122.8, 121.7, 120.7 (q, JC-F=324.2 Hz), 103.3, 102.4; HRMS (ESI) calcd for C12H7ClIO [MOTf]＋ 328.9225, found 328.9218.
3-Bromo-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2fa): 66% yield (171 mg), white solid, column chromatography [V(dichloromethane)∶V(me- thanol)=20∶1]. m.p. 195~197 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.17 (d, J=2.3 Hz, 1H), 8.03 (dd, J=8.1, 1.3 Hz, 1H), 7.88 (dd, J=8.7, 2.3 Hz, 1H), 7.74~7.64 (m, 3H), 7.47 (ddd, J=8.6, 6.7, 2.1 Hz, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 153.3, 153.1, 136.2, 135.2, 133.6, 133.5, 128.4, 123.2, 121.7, 120.7 (q, JC-F=323.2 Hz), 118.8, 103.8, 102.4; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C12H7BrIO [MOTf]＋ 372.8719, found 372.8714.
2-Chloro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluo- romethanesulfonate (2ga): 80% yield (191 mg), white solid, column chromatography [V(dichloromethane)∶V(me- thanol)=20∶1]. m.p. 170~172 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.08~8.02 (m, 2H), 7.89 (d, J=2.3 Hz, 1H), 7.69 (d, J=3.8 Hz, 2H), 7.55 (dd, J=8.7, 2.3 Hz, 1H), 7.48~7.43 (m, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 154.4, 153.2, 137.7, 134.6, 133.6, 133.5, 128.5, 128.1, 121.8, 121.8, 120.7 (q, JC-F=323.2 Hz), 102.4, 101.1; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C12H7ClIO [MOTf]＋ 328.9225, found 328.9215.
2-(Trifluoromethyl)-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluoromethanesulfonate (2ha): 54% yield (138 mg), white solid, column chromatography [V(dichlorome- thane)∶V(methanol)=20∶1]. m.p. 204~210 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.28~8.24 (m, 1H), 8.15 (d, J=2.1 Hz, 1H), 8.05 (dd, J=8.1, 1.4 Hz, 1H), 7.85 (dd, J=8.6, 2.1 Hz, 1H), 7.77~7.68 (m, 2H), 7.49 (ddd, J=8.6, 7.1, 1.9 Hz, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 154.0, 153.1, 135.0, 133.6, 133.5, 133.4 (q, JC-F=32.3 Hz), 128.6, 124.5 (q, JC-F=4.0 Hz), 124.3, 121.7 (q, JC-F=21.2 Hz), 120.7 (q, JC-F=323.2 Hz), 118.7 (q, JC-F=4.0 Hz), 107.6, 102.2; 19F NMR (376 MHz, DMSO-d6) δ: 61.48 (s), 77.76 (s); HRMS (ESI) calcd for C13H7F3IO [MOTf]＋ 362.9488, found 362.9478.
Methyl 5-(((trifluoromethyl)sulfonyl)oxy)-5H-5λ3-di- benzo[b,e][1,4]iodaoxine-2-carboxylate (2ia): 87% yield (217 mg), white solid, column chromatography [V(dich- loromethane)∶V(methanol)=20∶1]. m.p. 170~172 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.12~8.07 (m, 2H), 8.00 (dd, J=8.1, 1.4 Hz, 1H), 7.85 (t, J=7.9 Hz, 1H), 7.77~7.67 (m, 2H), 7.52~7.45 (m, 1H), 4.04 (s, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 164.6, 153.8, 153.3, 134.4, 134.3, 133.6, 133.6, 128.5, 128.1, 121.9, 121.6, 120.7 (q, JC-F=323.2 Hz), 108.2, 102.5, 53.0; 19F NMR (376 MHz, DMSO-d6) δ: 77.77; HRMS (ESI) calcd for C14H10IO3 [MOTf]＋ 352.9669, found 352.9662.
1,3-Dichloro-5H-5λ3-dibenzo[b,e][1,4]iodaoxin-5-yl trifluoromethanesulfonate (2ja): 55% yield (141 mg), white solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 215~217 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.12~8.10 (m, 1H), 8.09~8.04 (m, 1H), 8.02 (d, J=2.4 Hz, 1H), 7.73~7.70 (m, 2H), 7.54~7.49 (m, 1H); 13C NMR (101 MHz, DMSO-d6) δ: 153.0, 148.7, 133.8, 133.7, 133.0, 131.6, 131.1, 128.9, 126.3, 121.9, 120.7 (q, JC-F=323.2 Hz), 105.6, 103.6; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C12H6Cl2IO [MOTf]＋ 362.8835, found 362.8828.
4.3 Synthesis and characterization of N-bridging heterocyclic diaryliodonium salts
An oven-dried Schlenk tube equipped with a Teflon cap and a magnetic stir bar, was charged with diaryliodonium salts (0.5 mmol, 1.0 equiv.) and DMAP (1.0 equiv.). The tube was filled with nitrogen for three times, then MeCN (3 mL) was added. The mixture was allowed to be stirred at 80 ℃ for 12 h. After cooling to room temperature, and TLC indicated that the iodonium salts were completely consumed. Then selective fluorine reagent (2.0 mmol, 4 equiv.) was added, followed by the addition of 0.5 mL of acetic acid as ligand, continued the reaction at room temperature for 24 h. After the reaction was detected by TLC, trifluoromethanesulfonic acid (2.0 mmol, 4 equiv.) was added under an ice bath, stirred for 10 min, and transferred the reaction to 80 ℃ to continue the reaction for 2 h, and the product was obtained.
10-(Phenylsulfonyl)-5λ3-dibenzo[b,e][1,4]iodazin-5(10H)-yl trifluoromethanesulfonate (4aa): 60% yield (135 mg), light yellow solid, column chromatography [V(di- chloromethane)∶V(methanol)=20∶1]. m.p. 202~204 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 7.99 (ddd, J=8.0, 4.3, 1.5 Hz, 4H), 7.86 (t, J=7.5 Hz, 1H), 7.80~7.74 (m, 2H), 7.67~7.61 (m, 2H), 7.58 (t, J=7.8 Hz, 2H), 7.47 (d, J=7.3 Hz, 2H); 13C NMR (101 MHz, DMSO-d6) δ: 137.9, 136.7, 134.5, 133.9, 132.3, 131.6, 130.4, 130.2, 126.8, 120.4 (q, JC-F=325.2 Hz), 113.9; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C18H13INO2S [MOTf]＋ 433.9706, found 433.9697.
10-((4-Chlorophenyl)sulfonyl)-5λ3-dibenzo[b,e][1,4]-iodazin-5(10H)-yl trifluoromethanesulfonate (4ab): 77% yield (238 mg), white solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 204~206 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.00 (dd, J=8.1, 1.5 Hz, 4H), 7.79 (td, J=7.7, 1.4 Hz, 2H), 7.74~7.68 (m, 2H), 7.60 (td, J=7.8, 1.5 Hz, 2H), 7.47~7.43 (m, 2H); 13C NMR (101 MHz, DMSO-d6) δ: 139.9, 137.0, 136.7, 134.3, 132.7, 132.1, 130.9, 130.8, 128.9, 120.7 (q, JC-F=324.2 Hz), 114.0; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C18H12NClISO2 [M OTf]＋ 467.9316, found 467.9300.
10-((4-Bromophenyl)sulfonyl)-5λ3-dibenzo[b,e][1,4]io-dazin-5(10H)-yl trifluoromethanesulfonate (4ac): 62% yield (206 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 206~208 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.00 (dd, J=8.1, 1.5 Hz, 4H), 7.87~7.83 (m, 2H), 7.79 (td, J=7.7, 1.4 Hz, 2H), 7.60 (td, J=7.8, 1.5 Hz, 2H), 7.38~7.33 (m, 2H); 13C NMR (101 MHz, DMSO-d6) δ: 137.4, 136.7, 134.3, 133.7, 132.7, 132.1, 130.9, 129.0, 128.9, 121.0 (q, JC-F=324.2 Hz), 114.0; 19F NMR (376 MHz, DMSO-d6) δ: 77.74; HRMS (ESI) calcd for C18H12NBrISO2 [MOTf]＋ 511.8811, found 511.8796.
10-((4-(tert-Butyl)phenyl)sulfonyl)-5λ3-dibenzo[b,e]-[1,4]iodazin-5(10H)-yl trifluoromethanesulfonate (4ad): 59% yield (113 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 204~206 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.02 (dd, J=8.3, 1.3 Hz, 2H), 7.98 (dd, J=8.1, 1.5 Hz, 2H), 7.78 (td, J=7.7, 1.4 Hz, 2H), 7.64~7.55 (m, 4H), 7.40 (d, J=8.4 Hz, 2H), 1.32 (s, 9H); 13C NMR (101 MHz, DMSO-d6) δ: 158.1, 137.1, 135.5, 134.3, 132.6, 131.9, 130.7, 127.3, 126.9, 120.6 (q, JC-F=323.4 Hz), 114.0, 35.2, 30.8; 19F NMR (376 MHz, DMSO-d6) δ: 77.75; HRMS (ESI) calcd for C22H21NISO2 [MOTf]＋ 490.0332, found 490.0314.
10-Tosyl-5λ3-dibenzo[b,e][1,4]iodazin-5(10H)-yl trifluoromethanesulfonate (4ae): 58% yield (172 mg), light yellow solid, column chromatography [V(dichlorome- thane)∶V(methanol)=20∶1]. m.p. 190~192 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 7.98 (dt, J=7.8, 3.9 Hz, 4H), 7.77 (td, J=8.1, 7.7, 3.7 Hz, 2H), 7.57 (td, J=8.0, 3.4 Hz, 2H), 7.43 (dd, J=8.6, 3.5 Hz, 2H), 7.35 (dd, J=8.6, 3.1 Hz, 2H), 2.43 (s, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 145.5, 137.0, 135.4, 134.2, 132.6, 131.9, 131.0, 130.7, 127.2, 121.0 (q, JC-F=324.0 Hz), 114.0, 21.3; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C14H13NISO2 [MOTf]＋ 385.9706, found 385.9690. Analytical data are in agreement with the reported ones.[8]
10-((3,5-Difluorophenyl)sulfonyl)-5λ3-dibenzo[b,e][1,4]iodazin-5(10H)-yl trifluoromethanesulfonate (4af): 73% yield (226 mg), light yellow solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. m.p. 214~216 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.02 (ddd, J=13.9, 8.1, 1.4 Hz, 4H), 7.93 (tt, J=9.1, 2.3 Hz, 1H), 7.79 (td, J=7.7, 1.4 Hz, 2H), 7.61 (td, J=7.8, 1.5 Hz, 2H), 7.20~7.14 (m, 2H); 13C NMR (101 MHz, DMSO-d6) δ: 162.9 (dd, JC-F=252.2, 13.1 Hz), 141.0 (t, JC-F=8.1 Hz), 136.6, 134.4, 132.7, 131.9, 131.0, 120.7 (q, JC-F=323.2 Hz), 114.8, 110.8 (dd, JC-F=8.1, 4.0 Hz), 109.7 (t, JC-F=26.8 Hz); 19F NMR (376 MHz, DMSO-d6) δ: 77.76 (s), 103.50 (s); HRMS (ESI) calcd for C18H11NF2ISO2 [MOTf]＋ 469.9518, found 469.9496.
10-(Ethylsulfonyl)-5λ3-dibenzo[b,e][1,4]iodazin-5(10-H)-yl trifluoromethanesulfonate (4ag): 90% yield (145 mg), light yellow solid, column chromatography [V(dichlo- romethane)∶V(methanol)=20∶1]. m.p. 150~152 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.14 (dd, J=8.2, 1.4 Hz, 2H), 7.98 (dd, J=8.1, 1.5 Hz, 2H), 7.75 (td, J=7.7, 1.4 Hz, 2H), 7.58 (td, J=7.8, 1.5 Hz, 2H), 3.75 (q, J=7.3 Hz, 2H), 1.42 (t, J=7.3 Hz, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 138.5, 134.5, 132.9, 130.5, 130.1, 120.5 (q, JC-F=323.0 Hz), 117.2, 49.5, 22.6; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C14H13N- ISO2 [MOTf]＋ 385.9706, found 385.9690.
3-Chloro-10-(ethylsulfonyl)-5λ3-dibenzo[b,e][1,4]ioda-zin-5(10H)-yl trifluoromethanesulfonate (4ba): 58% yield (148 mg), oily liquid in tan, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. 1H NMR (400 MHz, DMSO-d6) δ: 8.2 (d, J=2.4 Hz, 1H), 8.2 (dd, J=8.2, 1.4 Hz, 1H), 8.0 (d, J=8.6 Hz, 2H), 7.8 (dd, J=8.6, 2.4 Hz, 1H), 7.8 (td, J=7.7, 1.4 Hz, 1H), 7.6 (td, J=7.8, 1.5 Hz, 1H), 3.8 (q, J=7.3 Hz, 2H), 1.4 (t, J=7.3 Hz, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 138.3, 137.8, 134.5, 133.8, 133.7, 132.9, 132.7, 131.1, 130.6, 130.2, 120.7 (q, JC-F=324.2 Hz), 118.1, 117.3, 49.4, 8.2; 19F NMR (376 MHz, DMSO-d6) δ: 77.8; HRMS (ESI) calcd for C14H12NClISO2 [MOTf]＋ 419.9316, found 419.9300.
10-(Ethylsulfonyl)-3-methyl-5λ3-dibenzo[b,e][1,4]ioda-zin-5(10H)-yl trifluoromethanesulfonate (4ca): 50% yield (136 mg), brown solid, column chromatography [V(di- chloro-methane)∶V(methanol)=20∶1]. m.p. 130~132 ℃; 1H NMR (400 MHz, DMSO-d6) δ: 8.14 (dd, J=8.1, 1.4 Hz, 1H), 7.97~7.93 (m, 2H), 7.85 (d, J=8.2 Hz, 2H), 7.74 (td, J=7.7, 1.4 Hz, 1H), 7.61~7.51 (m, 2H), 3.72 (q, J=7.3 Hz, 2H), 2.41 (s, 3H), 1.41 (t, J=7.3 Hz, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 140.7, 138.7, 135.9, 134.5, 134.3, 133.3, 132.8, 130.3, 130.1, 129.6, 120.7 (q, JC-F=324.2 Hz), 117.1, 117.0, 49.3, 20.4, 8.3; 19F NMR (376 MHz, DMSO-d6) δ: 77.76; HRMS (ESI) calcd for C15H15NISO2 [MOTf]＋ 399.9863, found 399.9848.
10-(Ethylsulfonyl)-3-fluoro-5λ3-dibenzo[b,e][1,4]ioda-zin-5(10H)-yl trifluoromethanesulfonate (4da): 48% yield (132 mg), brown oily liquid solid, column chromatography [V(dichloromethane)∶V(methanol)=20∶1]. 1H NMR (400 MHz, DMSO-d6) δ: 8.2 (dd, J=8.2, 1.4 Hz, 1H), 8.0~8.0 (m, 2H), 8.0 (dd, J=8.0, 1.5 Hz, 1H), 7.8 (td, J=7.7, 1.4 Hz, 1H), 7.6 (td, J=8.5, 2.9 Hz, 1H), 7.6~7.5 (m, 1H), 3.7 (q, J=7.3 Hz, 2H), 1.4 (t, J=7.3 Hz, 3H); 13C NMR (101 MHz, DMSO-d6) δ: 160.6 (d, JC-F=253.5 Hz), 138.5, 135.4 (d, JC-F=3.0 Hz), 134.5, 132.9, 131.5 (d, JC-F=9.1 Hz), 130.5, 130.3, 121.5 (d, JC-F=27.3 Hz), 120.7 (q, JC-F=323.2 Hz), 120.0 (d, JC-F=22.2 Hz), 118.1 (d, JC-F=9.1 Hz), 117.7, 49.4, 8.2; 19F NMR (376 MHz, DMSO-d6) δ: 77.7, 109.5 (td, J=8.5, 5.3 Hz); HRMS (ESI) calcd for C14H12NFISO2 [MOTf]＋ 403.9612, found 403.9594.
4.2 Synthesis and characterization of 2aj'/2ak'
To an oven-dried Schlenk tube was added iodonium salts 2aj/2ak (0.5 mmol, 1 equiv.), Pd/C (0.0025 mmol, 0.05 equiv.) and NaOAc (1.5 mmol, 3 equiv.) in 5 mL of DMA. The mixture is then stirred at 140 ℃ for 24 h. After TLC indicated that the diaryliodonium salts were completely consumed, the mixture was cooled to room temperature and water was added (20 mL). Then extracted with ethyl acetate and dried over anhydrous Na2SO4 and concentrated in vacuo. The crude compound was purified by column chromatography on silica gel to give white solid, (2aj' 100 mg, 80% yield, and 2ak' 116 mg, 74% yield).
3-Methyl-2H-benzofuro[2,3-g]chromen-2-one (2aj'): 1H NMR (400 MHz, CDCl3) δ: 8.14 (d, J=0.8 Hz, 1H), 8.02 (d, J=7.8 Hz, 1H), 7.56 (dd, J=8.6, 5.4 Hz, 2H), 7.49~7.44 (m, 1H), 7.37~7.32 (m, 1H), 7.31 (d, J=8.9 Hz, 1H), 2.27 (d, J=1.2 Hz, 3H); 13C NMR (101 MHz, CDCl3) δ: 162.1, 157.1, 152.3, 149.9, 135.4, 127.9, 126.9, 123.5, 123.4, 122.0, 119.2, 115.8, 114.2, 114.0, 112.5, 17.8; HRMS (EI-TOF) calcd for C16H10O3 250.0624, found 250.0632.
3-(Dibenzo[b,d]furan-2-yl)-2H-chromen-2-one (2ak'): 1H NMR (400 MHz, CDCl3) δ: 8.34 (d, J=1.7 Hz, 1H), 8.00 (d, J=7.6 Hz, 1H), 7.90 (s, 1H), 7.79 (dd, J=8.6, 1.9 Hz, 1H), 7.63 (d, J=8.6 Hz, 1H), 7.61~7.54 (m, 3H), 7.52~7.46 (m, 1H), 7.42~7.37 (m, 2H), 7.35~7.29 (m, 1H); 13C NMR (101 MHz, CDCl3) δ: 161.0, 156.8, 156.5, 153.6, 140.0, 131.5, 129.6, 128.4, 128.0, 127.9, 127.6, 124.7, 124.6, 124.1, 123.1, 121.3, 121.1, 119.9, 116.6, 111.9, 111.8; HRMS (EI-TOF) calcd for C21H12O3 312.0781, found 312.0789.
Supporting Information NMR spectra of 2aa~2ja, 4aa~4fa, 2aj' and 2ak'. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn.
(Cheng, F.)