English

• 1.   Introduction

  Fluorine-containing molecules are of great interest in the pharmaceutical, agrochemical and materials.^[1] Despite the widespread distribution of fluorine in nature, the natural fluorinated organic molecules are very rare. Thus, the development of new efficient methods for the selective fluorination of organic compounds has received increasing attention in the past few years.^[2] Among them, the fluorination of alkenes, such as aminofluorination, oxyfluorination and carbofluorination, represents one of the most efficient ways to synthesize various alkyl fluorides, which have been well studied in recent decades.^[3] In contrast, few reports on the fluoroarylation of alkenes have been disclosed.^[7~9]

  In 2014, Toste et al.^[7] developed a palladium-catalyzed intermolecular fluoroarylation of styrenes using aryl boronic acids as aryl source, in which the amide-based directing groups are essential to stabilize alkyl-palladium intermediate (Scheme 1a). Later, an elegant Pd-catalyzed 1, 1-fluoroarylation of unactivated alkenes was also reported by the same group, where this reaction proceeded through an oxidative Heck type mechanism involving β-hydride elimination, reinsertion and oxidative fluorination.^[7] Meanwhile, Loh and Feng et al.^[8] reported a palladium-catalyzed fluoroarylation of gem-difluoroalkenes to afford the 1, 1, 1-trifluoro-2-arylalkanes using aryl iodides as aryl source (Scheme 1b). With radical process, Tang and coworkers reported a silver-catalyzed Meerwein fluoroarylation of styrenes using aryl diazonium salts as aryl sources (Scheme 1c).^[9] In these reactions, prefunctionalized aryl reagents were required; arguably, fluoroarylation of alkenes through C―H functionalization of simple arenes should be the privileged strategy (Scheme 1d). Herein, we described a novel palladium-catalyzed intramolecular fluoroarylation of alkenes with ArIF₂ as the fluorine source, in which the arene tethered with alkenes was used as aryl source. This method provided a convenient protocol for the synthesis of fluorinated tetraline derivatives.

  Scheme 1

  

  Scheme 1.  Transition metal-catalyzed fluoroarylation of alkenes.

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  2.   Results and discussion

  As our continuous research interest in difunctionalization of alkenes, ^[10] recently we have developed the inter-molecular oxy-, azido- and fluoro-carbonylation reactions of unactivated alkenes under CO atmosphere, using various hypervalent iodine reagents, such as PhI(OAc)₂, ArI(N₃) and ArIF₂, which afforded a serial of β-functionalized carboxylic acid derivatives.^[11] For example, treatment of 4-phenyl-1-buytene by ArIF₂ and PdCl₂ under CO atmosphere afforded the desired fluorocarbonylation product in good yield. Further mechanistic study revealed that the reaction was initiated from an iodonium species, followed by a nucleophilic ring-opening by palladium catalyst and CO insertion. However, the control experiments revealed that the fluorinated tetraline was observed in the absence of CO (Scheme 2), which was a core structure in the medicinal and bioactive compounds.^[12] So far, there is no efficient method for the access to these compounds.^[13] Thus the fluoroarylation of alkenes aroused our great interest.

  Scheme 2

  

  Scheme 2.  Pd-catalyzed fluorination of alkenes

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  With above observation, further optimizing reaction conditions were surveyed. The reaction of 1a was initially tested by using PdCl₂ catalyst and ArIF₂ to give the 2-fluorotetralin (2a) in 26% yield (Table 1, Entry 1). Further screening of palladium catalysts revealed that Pd(Ph-CN)₂Cl₂ was the best catalyst to give the product 2a in 42% yield (Table 1, Entries 1~3). Addition of tetrahydrofuran (THF) was slightly helpful to the yield (Entry 4). Later, the yield was further improved to 60% by adding 5 Å molecular sieves and lowering down the temperature to 0 ℃ (Entries 5, 6), which is possibly to stabilize ArIF₂. In our previous report, Lewis acid such as BF₃•OEt₂ was required to activate PhI(OAc)₂, thus producing the cationic PhI(OAc)⁺ species which reacts with the alkene to form the three-membered iodonium ion intermediate.^[14] Thus, both Lewis and Bronsted acids were screened, and tris(penta-fluorophenyl)borate [B(C₆F₅)₃] gave the best result to afford 2a in 76% NMR yield and 70% isolated yield (Entries 7~10). Control experiments showed that no reaction occurred in the absence of palladium catalyst (Entry 11). Meanwhile, absence of Lewis acid significantly decreased the yield of prodcuct 2a to 15% yield (Entry 12), highlighting the important role of Lewis acid. Other transition metal salts were also surveyed, but CuCl₂ and AlCl₃ could not catalyze this reaction and only small amount of desired product 2a was detected in the cases of NiCl₂ and PtCl₂ (Entries 13~16).

  Table 1

  

  Table 1.  Optimization of the reaction condition^a

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  Entry	Cat.	Additive	Solvent (V:V)	Yieldb/%
  1	PdCl2	BF3•Et2O	MeCN	26
  2	Pd(CH3CN)2Cl2	BF3•Et2O	MeCN	37
  3	Pd(PhCN)2Cl2	BF3•Et2O	MeCN	42
  4	Pd(PhCN)2Cl2	BF3•Et2O	MeCN/THF (9:1)	48
  5c	Pd(PhCN)2Cl2	BF3•Et2O	MeCN/THF (9:1)	53
  6c, d	Pd(PhCN)2Cl2	BF3•Et2O	MeCN/THF (9:1)	60
  7c, d	Pd(PhCN)2Cl2	BPh3	MeCN/THF (9:1)	0
  8c, d	Pd(PhCN)2Cl2	B(C6F5)3	MeCN/THF (9:1)	76 (70)e
  9c, d	Pd(PhCN)2Cl2	TsOH	MeCN/THF (9:1)	15
  10c, d	Pd(PhCN)2Cl2	TfOH	MeCN/THF (9:1)	23
  11c, d	―	B(C6F5)3	MeCN/THF (9:1)	0
  12c, d	Pd(PhCN)2Cl2	―	MeCN/THF (9:1)	15
  13c, d	CuCl2	B(C6F5)3	MeCN/THF (9:1)	0
  14c, d	AlCl3	B(C6F5)3	MeCN/THF (9:1)	0
  15c, d	NiCl2	B(C6F5)3	MeCN/THF (9:1)	16
  16c, d	PtCl2	B(C6F5)3	MeCN/THF (9:1)	24
  a All reactions were run at 0.2 mmol scale with ArIF2 (5 equiv). b Yields were obtained by 1H NMR with CH3NO2 as an internal standard. c Addition of 5 Å molecular sieves (25 mg). d 0 ℃. e Isolated yield indicated in parentheses.

  With the optimized reaction conditions in hand, we turned our attention to examine the substrate scope of alkenes. As shown in Table 2, various substrates with substituted arenes were tested. However, the reactions afforded the six-membered products 2 and 3, where the regioisomers located in the aryl ring. For instance, substrates bearing neutral or electron-rich arenes (1b~1d) gave a mixture of 2b~2d and 3b~3d in good yields, but low regioselectivities (1.1~1.4:1) (Entries 2~4). The methyl group located in different position of phenyl (1b~1c) didn't exhibit significant effect on the yields. The reaction of substrate 1e also smoothly proceeded to give fluoroarylation product 2e and 3e in 70% yield with 1.6:1 regioselectivity (Entry 5). Moreover, substrates bearing para-halogenated arenes 1f~1h were also suitable for the reaction to give the desired products 2f~2h and 3f~3h in moderate yields with 1~1.5:1 ratio (Entries 6~8). Interestingly, when substrate 1i bears an electron-deficient arene with CF₃ group in para position, the reaction exhibited excellent selectivity to afford the desired product 2i as a single product, albeit in slightly low yield (34%, Entry 9). Furthermore, the reaction of but-3-ene-1, 1-diyl-dibenzene (1j) also exhibited excellent reactivity to generate single product 2j with excellent diastereoselectivity ratio (Entry 10). The reaction was not limited to butenyl arenes substrates, phenylallyl ethers 1k and 1l were proven to be good substrates, and the reaction furnished the fluoroarylation products 2k and 2l in moderate to good yields (Entries 11, 12). Notably, the reaction of 1l preformed excellent selectivity, and only single product 2l was observed (Entry 12).

  Table 2

  

  Table 2.  Substrate scope for intramolecular fluoroarylation^a

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  As similar to our previous reports, ^[11] both Lewis acid and palladium catalyst were required to the current reaction. Thus we propose that the reaction is initiated by the same iodonium intermediate int.Ⅰ, in which Lewis acid [B(C₆F₅)₃] plays an important role to activate ArIF₂ (Scheme 3, path a). After that, the reaction is followed by the ring-opening of iodonium int.Ⅰ with nucleophilic attack by Pd(Ⅱ) species to generate the key palladium(Ⅳ) intermediate int.Ⅱ.

  Scheme 3

  

  Scheme 3.  Plausible reaction mechanism

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  As mentioned in above, the reactions afforded the mixture of isomers 2 and 3 (Table 2). It suggests that a key intermediate int-Ⅲ is possibly involved, and this species could be formed through an intramolecular electrophilic arylation of int-Ⅱ owing to the good leaving property of Pd(Ⅳ). The arenium ion int.Ⅲ undergoes C―C bond migration and deprotonation to afford intermediate int.Ⅳ, in which the nonselective migration results in two regioisomers in the cases of substrates with substituted arenes.^[15] Finally, nucleophilic fluorination of int.Ⅳ generates the desired product 2 and 3. This pathway is consistent with the substrate scope in Table 2, in which electron-rich arenes exhibit good reactivity.

  Alternatively, another possible mechanism involves a fluoropalladation pathway (path b), where the generated fluoroalkyl-Pd(Ⅱ) species int.Ⅴ could be further oxidized to give Pd(Ⅳ) species int.Ⅵ. With the following electrophilic arylation at Pd(Ⅳ) center, the migration of int.Ⅶ affords the final product. This pathway can not be ruled out at this stage, however, only fluoropalladation of styrenes was achieved in our previous studies, and unactivated alkenes was not successful.^[16]

  3.   Conclusions

  In summary, we developed a novel palladium-catalyzed intramolecular fluoroarylation of alkenes, in which ArIF₂ was employed as fluorine source as well as electrophilic reagent to activate olefin, which delivered the fluoroarylation products in moderate to good yields. It is notable that the arenes tethered with double bond was used as aryl source. The current method presents an efficient approach for the synthesis of fluorinated tetraline, but with poor regioselectivities.

  4.   Experimental section

  4.1   General consideration

  PdCl₂ was purchased from Strem Chemical, other commercial reagents with high purity were purchased and used without further purification, unless otherwise noted. Reactions were monitored by thin-layer chromatography (TLC) carried out on 25 mm silica gel plates. ¹H NMR, ¹⁹F NMR and ¹³C NMR spectra were recorded on an agilent-400 MHz spectrometer. The chemical shifts (δ) are given in parts per million relative to internal standard TMS (0 for ¹H), CDCl₃ (77.0 for ¹³C). Flash column chromatography was performed on silica gel (particle size 200~300 mesh, purchased from Canada) and eluted with petroleum ether/ethyl acetate. Acetonitrile and tetrahydrofuran were directly obtained from solvent purification system of Innovation Technology Company. Substrates 1a~1i, ^[15] 1j, ^[17] 1k^[18] and 1l^[19] were prepared according to the literatures.

  4.2   General procedure for intermolecular fluorocarbonylation of alkenes

  In an oven-dried Schlenk tube (10 mL), Pd(PhCN)₂Cl₂ (7.6 mg, 0.02 mmol), ArIF₂ (270 mg, 1.0 mmol) and 5 Å molecular sieves (25 mg) were dissolved in a mixture solvent of CH₃CN and THF (1.0 mL, V:V＝9:1), then B(C₆F₅)₃ (30.7 mg, 0.06 mmol) and alkene substrate 1 (0.2 mmol) were added at 0 ℃. The mixture was stirred at 0 ℃ for 24 h. Then the organic solvent was removed under vacuum, and the residue was diluted by EtOAc (4.0 mL) and filtrated through a short pad of silica gel. The filtrate was concentrated under vacuum, and the crude residue was purified by column chromatography on silica gel with a gradient eluant of petroleum ether and ethyl acetate to give a mixture of products 2 and 3.

  4.3   Compounds characterization

  2-Fluoro-1, 2, 3, 4-tetrahydronaphthalene (2a)^[13]: Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.15~7.07 (m, 4H), 5.14~5.01 (dm, J＝47.6 Hz, 1H), 3.18~2.97 (m, 3H), 2.81 (dt, J＝16.8, 6.4 Hz, 1H), 2.14~1.98 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 135.4 (d, J＝1.6 Hz), 132.9 (d, J＝6.0 Hz), 129.4, 128.5, 126.1, 126.0, 88.7 (d, J＝169.0 Hz), 35.3 (d, J＝22.0 Hz), 28.5 (d, J＝19.7 Hz), 25.5 (d, J＝8.9 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －177.4~－177.7 (m).

  2-Fluoro-7-methyl-1, 2, 3, 4-tetrahydronaphthalene (2b) and 2-fluoro-6-methyl-1, 2, 3, 4-tetrahydronaphthalene (3b): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.05~6.93 (m, 3H), 5.14~5.00 (dm, J＝49.2 Hz, 1H), 3.16~2.95 (m, 3H), 2.81~2.74 (m, 1H), 2.35~2.31 (m, 3H), 2.12~2.02 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 135.6, 135.2 (d, J＝1.6 Hz), 129.8 (d, J＝6.2 Hz), 129.3, 129.1, 126.9. 89.0 (d, J＝167.9 Hz), 34.9 (d, J＝22.3 Hz). 28.5 (d, J＝20.1 Hz), 25.6 (d, J＝8.9 Hz), 20.9; minor: 135.5, 132.3 (d, J＝1.5 Hz), 132.7 (d, J＝6.2 Hz), 129.9, 128.4, 127.0, 88.9 (d, J＝169.1 Hz), 35.0 (d, J＝22.2 Hz), 28.6 (d, J＝19.8 Hz), 25.2 (d, J＝8.3 Hz), 20.9; ¹⁹F NMR (376 MHz, CDCl₃) δ: 177.30~－177.61 (m). HRMS-EI calcd for C₁₁H₁₃F [M^•+] 164.1001, found 164.0998.

  2-Fluoro-5-methyl-1, 2, 3, 4-tetrahydronaphthalene (2c) and 2-fluoro-8-methyl-1, 2, 3, 4-tetrahydronaphthalene (3c): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.15~6.95 (m, 3H), 5.19~4.96 (m, 1H), 3.17~2.64 (m, 4H), 2.40~1.92 (m, 5H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 136.2, 133.8, 132.7 (d, J＝6.2 Hz), 128.4, 127.7, 127.2, 125.9, 88.6 (d, J＝168.5 Hz), 35.8 (d, J＝21.8 Hz), 28.5 (d, J＝21.6 Hz), 23.3 (d, J＝8.2 Hz), 19.6; minor: 136.8, 135.3, 131.6 (d, J＝5.9 Hz), 127.5, 126.3, 125.8, 89.2 (d, J＝168.0 Hz), 33.0 (d, J＝22.6 Hz), 28.1 (d, J＝19.9 Hz), 25.9 (d, J＝7.8 Hz), 19.5; ¹⁹F NMR (376 MHz, CDCl₃) δ: major: －178.5~－178.9 (m); minor: －175.6~－175.9 (m). HRMS-EI calcd for C₁₁H₁₃F [M^•+] 164.1001, found 164.1004.

  7-(tert-Butyl)-2-fluoro-1, 2, 3, 4-tetrahydronaphthalene (2d) and 6-(tert-butyl)-2-fluoro-1, 2, 3, 4-tetrahydrona-phthalene (3d): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.21~7.19 (m, 1H), 7.14~7.12 (m, 1H), 7.08~7.04 (m, 1H), 5.17~5.04 (dm, J＝50.0 Hz 1H), 3.22~2.98 (m, 3H), 2.87~2.77 (m, 1H), 2.19~2.07 (m, 2H), 1.52~1.34 (m, 9H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 149.1, 132.4, 129.9 (d, J＝6.5 Hz), 129.1, 125.3, 123.2, 89.0 (d, J＝169.9 Hz), 34.9 (d, J＝22.2 Hz), 31.3, 29.8, 28.6 (d, J＝20.2 Hz), 25.9 (d, J＝8.4 Hz); minor: 149.0, 134.8, 132.4, 129.9 (d, J＝6.5 Hz), 128.2, 126.1, 123.3, 89.0 (d, J＝169.9 Hz), 35.6 (d, J＝22.0 Hz), 31.3, 29.6, 28.6 (d, J＝20.2 Hz), 25.2 (d, J＝8.7 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －177.0~－177.8 (m). HRMS-EI calcd for C₁₄H₁₉F [M^•+] 206.1471, found 206.1474.

  2-Fluoro-7-phenyl-1, 2, 3, 4-tetrahydronaphthalene (2e) and 2-fluoro-6-phenyl-1, 2, 3, 4-tetrahydronaphthalene (3e): White solid, m.p. 36~37 ℃. ¹H NMR (400 MHz, CDCl₃) δ: 7.63 (d, J＝8.4 Hz, 2H), 7.48 (t, J＝7.6 Hz, 2H), 7.43 (d, J＝7.6 Hz, 1H), 7.40~7.37 (m, 2H), 7.29~7.06 (m, 2H), 5.30~4.98 (dm, J＝49.6 Hz, 1H), 3.30~3.06 (m, 3H), 2.95~2.85 (m, 1H), 2.26~2.06 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 141.0, 139.2, 135.8, 133.3 (d, J＝5.8 Hz), 129.8, 128.7, 128.0, 127.1, 127.0, 124.9, 88.7 (d, J＝169.1 Hz), 35.0 (d, J＝22.2 Hz), 28.4 (d, J＝20.0 Hz), 25.6 (d, J＝8.3 Hz); minor: 140.9, 139.1, 134.6, 132.0 (d, J＝5.9 Hz), 129.0, 128.9, 128.0, 127.2, 126.9, 125.0, 88.7 (d, J＝169.1 Hz), 35.4 (d, J＝22.2 Hz), 28.4 (d, J＝20.0 Hz), 25.1 (d, J＝8.5 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －177.7~－178.2 (m). HRMS-EI calcd for C₁₆H₁₅F₄ [M^•+] 226.1158, found 226.1162.

  2, 7-Difluoro-1, 2, 3, 4-tetrahydronaphthalene (2f) and 2, 6-difluoro-1, 2, 3, 4-tetrahydronaphthalene (3f): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.08~7.02 (m, 1H), 6.85~6.79 (m, 2H), 5.16~5.01 (dm, J＝49.6 Hz, 1H), 3.11~2.92 (m, 3H), 2.81~2.73 (m, 1H), 2.15~1.95 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 160.2 (d, J＝241.4 Hz), 137.4 (dd, J＝8.5, 1.8 Hz), 130.6 (d, J＝8.2 Hz), 128.3 (dd, J＝5.4, 2.2 Hz), 114.8 (d, J＝20.9 Hz), 113.1 (d, J＝20.8 Hz), 88.4 (d, J＝169.1 Hz), 34.7 (d, J＝23.2 Hz), 28.0 (d, J＝20.3 Hz), 23.5 (d, J＝7.9 Hz); minor: 160.1 (d, J＝241.9 Hz), 134.7 (dd, J＝8.5, 5.5 Hz), 130.9 (dd, J＝3.1, 1.8 Hz), 129.9 (d, J＝8.0 Hz), 115.4 (d, J＝20.9 Hz), 113.2 (d, J＝21.6 Hz), 88.1 (d, J＝169.4 Hz), 35.2 (dd, J＝22.8, 1.6 Hz), 28.3 (d, J＝20.1 Hz), 25.4 (dd, J＝8.3, 1.7 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: major: －117.3 (q, J＝8.7 Hz), －178.3~－178.8 (m); minor: －117.5 (q, J＝8.7 Hz), －178.3~－178.8 (m). HRMS-EI calcd for C₁₀H₁₀F₂ [M^•+] 168.0751, found 168.0749.

  7-Chloro-2-fluoro-1, 2, 3, 4-tetrahydronaphthalene (2g) and 6-chloro-2-fluoro-1, 2, 3, 4-tetrahydronaphthalene (3g): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.11~7.08 (m, 2H), 7.03~7.00 (m, 1H), 5.14~5.00 (dm, J＝49.6 Hz, 1H), 3.12~2.91 (m, 3H), 2.79~2.72 (m, 1H), 2.18~1.95 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 137.2, 131.9 (d, J＝13.5 Hz), 131.2 (d, J＝4.6 Hz), 130.6, 128.0, 126.1, 88.2 (d, J＝169.6 Hz), 34.6 (d, J＝22.1 Hz), 27.9 (d, J＝20.7 Hz), 25.1 (d, J＝7.4 Hz); minor: 134.6 (d, J＝4.8 Hz), 133.9, 131.9 (d, J＝13.5 Hz), 129.8, 129.0, 126.2, 88.0 (d, J＝169.2 Hz), 34.9 (d, J＝22.9 Hz), 28.1 (d, J＝19.7 Hz), 24.6 (d, J＝7.8 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －178.4~－178.9 (m). HRMS-EI calcd for C₁₀H₁₀FCl [M^•+] 184.0455, found 184.0456.

  7-Bromo-2-fluoro-1, 2, 3, 4-tetrahydronaphthalene (2h) and 6-bromo-2-fluoro-1, 2, 3, 4-tetrahydronaphthalene (3h): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.26~7.24 (m, 2H), 6.96~6.95 (m, 1H), 5.14~5.00 (dm, J＝49.6 Hz, 1H), 3.13~2.91 (m, 3H), 2.78~2.69 (m, 1H), 2.15~2.94 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: major: 135.1 (d, J＝4.9 Hz), 134.4, 131.2, 130.9, 129.1, 119.6, 88.0 (d, J＝169.1 Hz), 34.6 (d, J＝23.0 Hz), 28.0 (d, J＝20.3 Hz), 25.0 (d, J＝7.5 Hz); minor: 137.8, 131.9, 131.7 (d, J＝5.5 Hz), 130.1, 129.0, 119.4, 87.9 (d, J＝169.7 Hz), 34.8 (d, J＝21.9 Hz), 27.9 (d, J＝19.9 Hz), 24.8 (d, J＝7.6 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －178. 4~－179.0 (m). HRMS-EI calcd for C₁₀H₁₀FBr [M^•+] 227.9950, found 227.9956.

  2-Fluoro-7-(trifluoromethyl)-1, 2, 3, 4-tetrahydronaphthalene (2i): Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.38 (d, J＝8.4 Hz, 1H), 7.35 (s, 1H), 7.21 (d, J＝7.6 Hz, 1H), 5.13 (dm, J＝49.6 Hz, 1H), 3.15 (dd, J＝9.2, 4.0 Hz, 1H), 3.09 (d, J＝3.6 Hz, 1H), 3.03 (t, J＝8.4 Hz, 1H), 2.87~2.80 (m, 1H), 2.26~1.83 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 139.6, 133.5 (d, J＝5.0 Hz), 129.0, 128.6, 126.9 (d, J＝271.6 Hz), 126.2 (q, J＝3.8 Hz), 122.8 (q, J＝4.0 Hz), 87.8 (d, J＝169.3 Hz), 35.0 (d, J＝22.4 Hz), 27.9 (d, J＝20.5 Hz), 25.1 (d, J＝8.1 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －62.0 (s), －178.7~－179.0 (m). HRMS-EI calcd for C₁₁H₁₀F₄ [M^•+] 218.0719, found 218.0713.

  3-Fluoro-1-phenyl-1, 2, 3, 4-tetrahydronaphthalene (2j): White solid, m.p. 38~38 ℃. ¹H NMR (400 MHz, CDCl₃) δ: 7.30 (t, J＝7.6 Hz, 1H), 7.25~7.23 (m, 1H), 7.15~7.12 (m, 4H), 7.10~7.05 (m, 1H), 6.84 (d, J＝7.6 Hz, 1H), 5.23~5-09 (dm, J＝49.6 Hz, 1H), 4.35 (dd, J＝8.8, 6.0 Hz, 1H), 3.30~3.09 (m, 2H), 2.49~2.41 (m, 1H), 2.18~2.04 (dd, J＝33.6, 10.0 Hz, 1H); ¹³C NMR (100 MHz, CDCl₃) δ: 145.7, 138.3, 133.0 (d, J＝3.6 Hz), 129.4, 129.2, 128.7, 128.5, 126.4, 126.2, 87.3 (d, J＝165.6 Hz), 41.7 (d, J＝6.3 Hz), 37.6 (d, J＝19.7 Hz), 35.4 (d, J＝22.4 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －180.7~－181.2 (m). HRMS-EI calcd for C₁₆H₁₅F [M^•+] 226.1158, found 226.1163.

  3-Fluorochromane (2k)^[20]: Colorless oil. ¹H NMR (400 MHz, CDCl₃) δ: 7.26~6.78 (m, 4H), 5.18~5.03 (dm, J＝47.6 Hz, 1H), 4.40~4.32 (m, 1H), 4.17~4.03 (m, 1H), 3.17~3.02 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 153.5, 130.0, 127.82, 121.2, 118.1, 116.7, 84.15 (d, J＝174.1 Hz), 66.9 (d, J＝21.9 Hz), 30.6 (d, J＝21.9 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －186.9~－187.3 (m). HRMS-EI calcd for C₉H₉OF [M^•+] 152.0637, found 152.0635.

  3-Fluoro-6-phenylchromane (2l): White solid. m.p. 38~38 ℃; ¹H NMR (400 MHz, CDCl₃) δ: 7.54 (d, J＝7.6 Hz, 2H), 7.44~7.37 (m, 3H), 7.34~7.31 (m, 2H), 6.95 (dd, J＝8.4, 1.2 Hz, 1H), 5.21~5.09 (dm, J＝47.6 Hz, 1H), 4.43~4.38 (m, 1H), 4.15 (dd, J＝31.2, 12.0 Hz, 1H), 3.27~3.12 (m, 2H); ¹³C NMR (100 MHz, CDCl₃) δ: 153.1, 140.6, 134.4, 128.7, 128.6, 126.8, 126.7, 126.6, 118.3, 117.0, 84.1 (d, J＝175.0 Hz), 67.0 (d, J＝21.1 Hz), 30.7 (d, J＝23.0 Hz); ¹⁹F NMR (376 MHz, CDCl₃) δ: －186.9~－187.3 (m). HRMS-EI calcd for C₁₅H₁₃OF [M^•+] 228.0950, found 228.0954.

  Supporting Information    ¹H NMR, ¹³C NMR and ¹⁹F NMR spectra for products 2/3a~2/3l. The Supporting Information is available free of charge via the Internet at http://sioc-journal.cn/.

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• 

  Scheme 1  Transition metal-catalyzed fluoroarylation of alkenes.

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  Scheme 2  Pd-catalyzed fluorination of alkenes

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  Scheme 3  Plausible reaction mechanism

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  Table 1.  Optimization of the reaction condition^a

  Entry	Cat.	Additive	Solvent (V:V)	Yieldb/%
  1	PdCl2	BF3•Et2O	MeCN	26
  2	Pd(CH3CN)2Cl2	BF3•Et2O	MeCN	37
  3	Pd(PhCN)2Cl2	BF3•Et2O	MeCN	42
  4	Pd(PhCN)2Cl2	BF3•Et2O	MeCN/THF (9:1)	48
  5c	Pd(PhCN)2Cl2	BF3•Et2O	MeCN/THF (9:1)	53
  6c, d	Pd(PhCN)2Cl2	BF3•Et2O	MeCN/THF (9:1)	60
  7c, d	Pd(PhCN)2Cl2	BPh3	MeCN/THF (9:1)	0
  8c, d	Pd(PhCN)2Cl2	B(C6F5)3	MeCN/THF (9:1)	76 (70)e
  9c, d	Pd(PhCN)2Cl2	TsOH	MeCN/THF (9:1)	15
  10c, d	Pd(PhCN)2Cl2	TfOH	MeCN/THF (9:1)	23
  11c, d	―	B(C6F5)3	MeCN/THF (9:1)	0
  12c, d	Pd(PhCN)2Cl2	―	MeCN/THF (9:1)	15
  13c, d	CuCl2	B(C6F5)3	MeCN/THF (9:1)	0
  14c, d	AlCl3	B(C6F5)3	MeCN/THF (9:1)	0
  15c, d	NiCl2	B(C6F5)3	MeCN/THF (9:1)	16
  16c, d	PtCl2	B(C6F5)3	MeCN/THF (9:1)	24
  a All reactions were run at 0.2 mmol scale with ArIF2 (5 equiv). b Yields were obtained by 1H NMR with CH3NO2 as an internal standard. c Addition of 5 Å molecular sieves (25 mg). d 0 ℃. e Isolated yield indicated in parentheses.

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  Table 2.  Substrate scope for intramolecular fluoroarylation^a

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•