Perfluoroalkylation

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Catalyst-free Decarboxylative Trifluoromethylation/ Perfluoroalkylation of Benzoic Acid Derivatives in Water–Acetonitrile Dangui Wang, Jingxian Fang, Guo-Jun Deng, and Hang Gong ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/acssuschemeng.7b01705 • Publication Date (Web): 14 Jul 2017 Downloaded from http://pubs.acs.org on July 14, 2017

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ACS Sustainable Chemistry & Engineering

Catalyst-free Decarboxylative Trifluoromethylation/ Perfluoroalkylation of Benzoic Acid Derivatives in Water–Acetonitrile Dangui Wang, Jingxian Fang, Guo-Jun Deng, and Hang Gong* The Key Laboratory of Environmentally Friendly Chemistry and Application of the Ministry of Education, College of Chemistry, Xiangtan University, Xiangtan 411105 P. R. China. *E-mail: [email protected]

ABSTRACT: This study presents a mild and practical method for the catalyst-free decarboxylative trifluoromethylation/perfluoroalkylation of benzoic acid derivatives by using inexpensive NaSO2CF3 as a CF3-source and solid Na2S2O8 as an initiator. The environmentfriendly transformation is performed at 30 °C in water–acetonitrile, and it can be easily scaled up to the gram level with a good yield.

KEYWORDS: Trifluoromethylation, Metal-free, Decarboxylation, Environmentally friendly chemistry INTRODUCTION Although trifluoromethyl is not a naturally occurring substance, it is still a popular component for numerous compounds.1-4 These compounds are widely applied in various fields, especially in

ACS Paragon Plus Environment

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pesticides and pharmaceuticals (Figure 1).5-9 The physical and biological properties, such as solubility, lipophilicity, and catabolic stability, of the parent molecules are remarkably modified by the trifluoromethyl group.5, 10-12 Thus, developing methods for the selective introduction of trifluoromethyl group into organic molecules is of great interest for scientists. Many functionalized compounds, such as alkyl/aryl halides or triflates, alkyl/aryl boronic derivatives, alkene, and alkyne were used as substrates for trifluoromethylation reactions.13 O2N H N

O

O F3C

N

O

F3C

Fluoxetine (Arava®) O

H N HCl

F3C

H N

F3C

HO

NH

O Nilutamide (Nilandron®) H2NSO 2

O O S

O

NC

F

Bicalutamide (Casodex ®) O F3C

O

N N

O

N N

NH N H

CF 3 CF 3 Fluoxetine (Prozac®)

Celecoxib (Celebrex® )

F Aprepitant (Emend® )

Figure 1. Examples of biologically active compounds of (trifluoromethyl)arenes. The direct C–H bond trifluoromethylation was also recently developed13-31 and reported by our group.32 In our previous work, arene was trifluoromethylated by using the inexpensive NaSO2CF3 (Langlois’ reagent) as the CF3-source and sodium persulfate as the initiator. When 2,4,6-trimethoxybenzoic acid was used as substrate, no desired direct C–H bond trifluoromethylation product was detected; however a 67% yield of the decarboxylative trifluoromethylation product was obtained. Despite the development of the decarboxylative trifluoromethylation reaction for other types of substrates have been developed (Scheme 1, A– C),33-37 to the best of our knowledge, no decarboxylative trifluoromethylation reaction of aromatic carboxylic acid was reported. In the current study, a mild, persulfate-induced method for the metal-free decarboxylative trifluoromethylation reaction of aromatic carboxylic acid in the presence of water was described (Scheme 1, E).


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Scheme 1. The reported decarboxylative trifluoromethylation reaction and our work. RESULTS AND DISCUSSION The initial investigation commenced with the decarboxylative trifluoromethylation reaction of 2,4,6-trimethoxybenzoic acid using sodium persulfate (1.5 equiv.) as the initiator, CF3SO2Na (Langlois’ reagent, 3.0 equiv.)38 as CF3-source, and water/acetonitrile (1.0 mL, 1:1) as the solvent at 30 °C under argon atmosphere (Table 1). The yield of the desired product was 67% (2a:3a = 46:21) (entry 1). First, the influence of reaction temperature was investigated, and results show that high temperature is unfavorable for this transformation (Table 1, entries 1–3). In studying the amount of CF3SO2Na, a slightly reduced yield of 57% can be obtained with better selectivity of mono substitution when 4 equiv. of CF3SO2Na was used. Hence, the amount of 4 equiv. of CF3SO2Na was used in the following study (Table 1, entries 1, 4–6). The reaction time was then studied, and the transformation was completed within 72 h; a prolonged reaction time is not beneficial for the reaction (Table 1, entries 5, 7–8). Several initiators were screened, and no better results were achieved (Table 1, entries 5, 9–11). A good yield of 77% was achieved when the amount of sodium persulfate was increased to 3 equiv (Table 1, entry 12). No better yield was observed when the amount of H3PO4 was adjusted (Table S1, entries 12, 15–18). Other additives such as HBF4, (n-C4H9)4NBr, and N,N-diisopropylethylamine were also evaluated, but


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only poor yields were achieved (Table S1, entries 19–21). Water and other mixture solvents were also examined, but the yield was only poor to moderate (Table S1, entries 22–29). When the reaction was conducted under air atmosphere, a slightly reduced yield of 62% was still obtained (Table 1, entry 15). By contrast, only a poor yield of 23% was achieved when the reaction was conducted under an atmosphere of oxygen (Table 1, entry 16). Table 1. Selected optimization results.a

Entry

Initiator (equiv.)

T (oC)

Yield(%) (2a:3a)

b

1 Na2S2O8 (1.5) 30 67(46/21) 2b Na2S2O8 (1.5) 50 59(38/21) 3b Na2S2O8 (1.5) 80 20(8/12) c 4 Na2S2O8 (1.5) 30 42(32/10) 5 Na2S2O8 (1.5) 30 57(49/8) d Na2S2O8 (1.5) 30 55(44/11) 6 7e Na2S2O8 (1.5) 30 52(42/10) f 8 Na2S2O8 (1.5) 30 62(52/10) 9 K2S2O8 (1.5) 30 23(15/8) 10 (NH4)2S2O8 (1.5) 30 32(21/11) 30 10(8/2) 11 t-BuOOH (1.5) 12 Na2S2O8 (3) 30 77(63/14) 13 Na2S2O8 (2) 30 67(51/16) 14 Na2S2O8 (1) 30 45(39/6) g 15 Na2S2O8 (3) 30 62(56/6) 16h Na2S2O8 (3) 30 23 a Unless otherwise noted, all reactions were conducted on a 0.1 mmol scale with 4 equiv. of CF3SO2Na, initiator and H3PO4 (1.5 mol%) in a sealed tube in CH3CN:H2O (0.5 mL: 0.5 mL) under an atmosphere of argon for 72 h. Yields are detected by GC-MS using naphthalene as internal standard. b 3 equiv. CF3SO2Na is used. c 5 equiv. CF3SO2Na is used. d 1.5 equiv. CF3SO2Na is used. e Reaction time is 48 h. f Reaction time is 96 h. g Under air atmosphere. h Under O2 atmosphere. The

scope

of

the

substrate

was

examined

using

the

reliable

decarboxylative

trifluoromethylation protocol (Tables 2 and S2). Nearly all benzoic acids substituted with electron-rich groups were converted into the desired trifluoromethylation product at good yields


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(Table 2, 2a–j). The yields of 2c and 2d are lower than those of 2a and 2b due to the influence of steric hindrance of substituents. Particularly, the selectivity of this reaction is extraordinary when asymmetrical benzoic acid was used as substrate. For example, the substituted products in situ are the main product when 1e was used as the substrate, whereas they become the minor product when 1f was used as the substrate. Almost a similar regularity was observed in the cases of using 1g/1h and 1i/1j as the substrates. The decarboxylative perfluoroalkylation of benzoic acid derivatives was also conducted, and a good yield was still achieved (Table 2, 2k–o). Unfortunately, no desired product was produced when less electron-rich or electron-poor aromatic acids were used as substrates (Table S2, 2k–o). This transformation is highly dependent on the electronic degree of the substrate. Table 2. Decarboxylative trifluoromethylation/ perfluoroalkylation of benzoic acid derivatives. a


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a

Unless otherwise noted, all reactions were conducted on a 0.1 mmol scale with RfSO2Na (4 equiv.), Na2S2O8 (3 equiv.) and H3PO4 (1.5 mol%) in a sealed tube in CH3CN:H2O (0.5 mL: 0.5 mL) under an atmosphere of argon for 72 h. The green star marked position is the original location of carboxyl. The isolated yield were presented. b CH3CN:H2O = 1 mL : 1 mL. This reaction can be easily scaled up to the half-gram level by using 1a (0.5 gram, 2.36 mmol) as the substrate, Na2S2O8 (3.0 equiv.), CF3SO2Na (4.0 equiv.), and H3PO4 (1.5 mol%) in a water–acetonitrile mixture (11.8 mL:11.8 mL) (Scheme 2). The mixture was stirred in a sealed tube under argon atmosphere at 30 °C for five days. A good yield of 68% can be obtained, which is comparable with the template reaction (Table 2, 2a).

Scheme 2. Half-gram reaction. Several control experiments were conducted to explore the reaction mechanism (Scheme 3). First, the reaction was conducted using 2,4,6-trimethoxybenzoic acid (1a) as a substrate in the absence of CF3SO2Na, and the decarboxylation product was detected in an essentially quantitative yield (Scheme 3, Eq. 1). Based on our previous study, the decarboxylation product can be easily converted to 1,3,5-trimethoxy-2-(trifluoromethyl)benzene (2a) at the standard reaction conditions.32 Afterwards, when 2,4,6-trimethoxy-3-(trifluoromethyl)benzoic acid was used in the absence of CF3SO2Na at the standard conditions, almost no decarboxylation product can be detected (Scheme 3, Eq. 2). These two experiments indicated that this reaction probably occurs in two steps. The first step is decarboxylation, followed by trifluoromethylation. Radical inhibition experiments were then performed (Scheme 3, Eqs. 3–4). When 1 equiv. benzoquinone or 1,1-diphenylethylene was added, only poor or trace amount of the desired product was detected, respectively. Thus, this radical process can be efficiently blocked by these two radical


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inhibitors. A deuteration study was also conducted. We performed the decarboxylative trifluoromethylation reaction in the mixture solvents of CH3CN:D2O = 0.5 mL:0.5 mL (Scheme 3, Eq. 5). The result showed the high deuterium ratio of the desired product. Afterward, 2,4,6trimethoxybenzoic

acid,

1,3,5-trimethoxybenzene

and

1,3,5-trimethoxy-2-

(trifluoromethyl)benzene were treated with D2O in the absence of CF3SO2Na (Scheme 3, eqs. 68). Both eq. 6 and eq. 7, the deuterated 1,3,5-trimethoxybenzene were obtained as the mainly product. However, in the case of eq. 8, only a poor deuterium ratio could be found. These results indicated that the reaction probably occurs in two steps, which containing decarboxylationaromatization and followed by a trifluoromethylation process. Based on these results and our previous investigation,32 a reasonable mechanism was proposed (Scheme 4). The carboxyl radical was formed in the presence of Na2S2O8, followed by decarboxylation to access the phenyl radical. Then, a hydrogen of water is captured by the phenyl radical to achieve the arene (Cycle I). Afterward, the Cycle II, which had been described in our previous work, 32 occurred which included a radical initial, followed by a radical addition, and the loss of hydrogen atom aromatization to form the target molecular (T.M.).


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OMe CO2H

OMe 98% GC-MS yield

Without CF3SO2Na Standard conditions

(1) MeO

OMe

MeO

OMe OMe

MeO

OMe

OMe CO2H

Without CF3SO2Na Standard conditions

(2) MeO

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OMe CF3 OMe CO2H

trace NMR yield

CF3 OMe CF3

Condition (3) or (4)

OMe CF3

+ MeO OMe MeO MeO OMe Radical inhibition experiments (3) Standard conditions, 1 equiv. benzoquinone added, GC yield: 8%. (4) Standard conditions, 1 equiv. 1,1-diphenylethylene added, GC yield: trace. (5) Deuteration Studies OMe OMe CO2H CF3 Standard conditions + MeO OMe CH3CN:D2O = 0.5 mL:0.5 mL MeO OMe MeO OMe H

OMe CF3

H

MeO H (5 (6) MeO

H

CF3

D

: OMe MeO

H

OMe H

H 9 OMe

H 16

:

:

MeO OMe GC-MS yield: 97% OMe D D

D

: OMe MeO

: OMe MeO

MeO

H

: OMe MeO D 20

:

OMe CF3 80)

OMe

OMe D

CF3

D

:

OMe MeO CF3 (20

D 71)

: : OMe COOH Standard conditions, without CF SO Na 3 2 CH CN:D = 0.5 mL:0.5 mL O 3 2 OMe OMe H

OMe CF3 11% OMe

CF3

OMe MeO

D 24

OMe CF3

46% OMe

OMe CF3

: OMe MeO

OMe CF3

OMe D 55

:

OMe Standard conditions, without CF3SO2Na

(7) MeO H

CH3CN:D2O = 0.5 mL:0.5 mL

OMe OMe H

H

H trace OMe

:

D

D

:

OMe MeO

OMe MeO D 19

:

OMe

OMe D 79

:

OMe CF3

MeO

H

H 2

MeO OMe

OMe D

:

: OMe MeO

MeO

(8)

OMe D

OMe

CF3

Standard conditions, without CF3SO2Na CH3CN:D2O = 0.5 mL:0.5 mL OMe

H

OMe CF3

H

: OMe MeO

MeO H 89

:

D

CF3

MeO OMe CF3

: OMe MeO D 11

:

OMe

OMe D trace

Scheme 3. Control experiments.


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Scheme 4. Proposed mechanism for the decarboxylative trifluoromethylation of benzoic acid. CONCLUSIONS The present study described a practical method for the catalyst-free decarboxylative trifluoromethylation of benzoic acid under mild reaction conditions using readily available CF3SO2Na as CF3-source. This strategy exhibits the advantages of water compatibility, operation safety, can be conducted at room temperature, and environment friendliness. In addition, this transformation can be easily scaled up to the gram level with good yield. Thus, the proposed strategy provides an avenue for introducing the trifluoromethyl and perfluoroalkyl groups into arenes. EXPERIMENTAL SECTION A solution of benzoic acid derivative (0.1 mmol), Na2S2O8 (3.0 equiv.), CF3SO2Na (4.0 equiv.), and H3PO4 (1.5 mol%) in a water–acetonitrile mixture (0.5 mL:0.5 mL) was stirred in a sealed tube under argon atmosphere at 30 °C for 72 h. The reaction mixture was then extracted with ethyl acetate. Afterwards, the combined organic phase was dried with Na2SO4, and the solvent


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was evaporated in vacuo. The residue was purified by preparative thin-layer chromatography on silica gel with petroleum ether and diethyl ether to yield the pure product.

ASSOCIATED CONTENT Supporting Information. The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acssuschemeng.xxxxxxx. Experimental details, and spectral data. (PDF) General information, selected optimization results and some failed substrates, preparation of substrates, experimental procedure and characterization data for products, and copies of 1H, 19

F and 13C NMR spectra.

AUTHOR INFORMATION Corresponding Author *E-mail: [email protected] Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest. ACKNOWLEDGMENT


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We are grateful to the National Natural Science Foundation of China (No. 21402168), Scientific Research Foundation of Hunan Provincial Education Department (No. 15B232) and Hunan 2011 Collaborative Innovation Center of Chemical Engineering & Technology with Environmental Benignity and Effective Resource Utilization for their support of our research. REFERENCES (1) Liu, X.; Xu, C.; Wang, M.; Liu, Q. Trifluoromethyltrimethylsilane: Nucleophilic trifluoromethylation and beyond. Chem. Rev. 2015, 115, 683-730. (2) Yang, X.; Wu, T.; Phipps, R. J.; Toste, F. D. Advances in catalytic enantioselective fluorination, mono-, di-, and trifluoromethylation, and trifluoromethylthiolation reactions. Chem. Rev. 2015, 115, 826-870. (3) Kirsch P. in Modern Fluoroorganic Chemistry, Wiley-VCH, Weinheim, 2004. (4) Prakash, G. K. S.; Wang, F.; O’Hagan, D.; Hu, J.; Ding, K.; Dai L.X. in Organic ChemistryBreakthroughs and Perspectives, Wiley-VCH, Weinheim, 2012. (5) Müller, K.; Faeh, C.; Diederich, F. Fluorine in pharmaceuticals: Looking beyond intuition. Science 2007, 317, 1881-1886. (6) Wang, J.; Sánchez-Roselló, M.; Aceña, J. L.; del Pozo, C.; Sorochinsky, A. E.; Fustero, S.; Soloshonok, V. A.; Liu, H. Fluorine in pharmaceutical industry: fluorine-containing drugs introduced to the market in the last decade (2001–2011). Chem. Rev. 2014, 114, 2432-2506. (7) Ojima I. in Fluorine in Medicinal Chemistry and Chemical Biology, Wiley-Blackwell, Oxford, 2009. (8) S. Purser, P. R. Moore, S. Swallow, V. Gouverneur, Chem. Soc. Rev. 2008, 37, 320-330. (9) H. L. Yale, J. Med. Pharm. Chem. 1959, 1, 121-133. (10) Hagmann, W. K. The many roles for fluorine in medicinal chemistry. J. Med. Chem. 2008, 51, 4359-4369. (11) Meanwell, N. A. Synopsis of some recent tactical application of bioisosteres in drug design. J. Med. Chem. 2011, 54, 2529-2591. (12) Zhou, Y.; Wang, J.; Gu, Z.; Wang, S.; Zhu, W.; Aceña, J. L.; Soloshonok, V. A.; Izawa, K.; Liu, H. Next generation of fluorine-containing pharmaceuticals, compounds currently in phase ii–iii clinical trials of major pharmaceutical companies: new structural trends and therapeutic areas. Chem. Rev. 2016, 116, 422-518. (13) Alonso, C.; de Marigorta, E. M.; Rubiales, G.; Palacios, F. Carbon trifluoromethylation reactions of hydrocarbon derivatives and heteroarenes. Chem. Rev. 2015, 115, 1847-1935. (14) Charpentier, J.; Fruh, N.; Togni, A. Electrophilic trifluoromethylation by use of hypervalent iodine reagents. Chem. Rev. 2015, 115, 650-654. (15) Tomashenko, O. A.; Grushin, V. V. Aromatic trifluoromethylation with metal complexes. Chem. Rev. 2011, 111, 4475-4521. (16) Fujiwara, Y.; Dixon, J. A.; O’Hara, F.; Funder, E. D.; Dixon, D. D.; Rodriguez, R. A.; Baxter, R. D.; Herle, B.; Sach, N.; Collins, M. R.; Ishihara, Y.; Baran, P. S. Practical and innate carbon–hydrogen functionalization of heterocycles. Nature 2012, 492, 95-99. (17) Nagib, D. A.; MacMillan, D. W. C. Trifluoromethylation of arenes and heteroarenes by means of photoredox catalysis. Nature 2011, 480, 224-228.


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(18) Furuya, T.; Kamlet, S. A.; Ritter, T. Catalysis for fluorination and trifluoromethylation. Nature 2011, 473, 470-477. (19) Nishida, T.; Ida, H.; Kuninobu, Y.; Kanai, M. Regioselective trifluoromethylation of Nheteroaromatic compounds using trifluoromethyldifluoroborane activator. Nat. Commun. 2014, 5, 3387-3392. (20) Li, L.; Mu, X.; Liu, W.; Wang, Y.; Mi, Z.; Li, C.-J. Simple and clean photoinduced aromatic trifluoromethylation reaction. J. Am. Chem. Soc. 2016, 138, 5809-5812. (21) Shang, M.; Sun, S.-Z.; Wang, H.-L.; Laforteza, B. N.; Dai, H.-X.; Yu, J.-Q. Exceedingly fast copper(ii)-promoted ortho C-H trifluoromethylation of arenes using tmscf3. Angew. Chem. Int. Ed. 2014, 53, 10439-10442. (22) Zhang, X.-G.; Dai, H.-X.; Wasa, M.; Yu, J.-Q. Pd(II)-catalyzed ortho trifluoromethylation of arenes and insights into the coordination mode of acidic amide directing groups. J. Am. Chem. Soc. 2012, 134, 11948-11951. (23) Hafner, A.; Bräse, S. Ortho-trifluoromethylation of functionalized aromatic triazenes. Angew. Chem. Int. Ed. 2012, 51, 3713-3715. (24) Mu, X.; Wu, T.; Wang, H.; Guo, Y.; Liu, G. Palladium-catalyzed oxidative aryltrifluoromethylation of activated alkenes at room temperature. J. Am. Chem. Soc. 2012, 134, 878-881. (25) Chu, L.; Qing, F.-L. Copper-catalyzed direct c–h oxidative trifluoromethylation of heteroarenes. J. Am. Chem. Soc. 2012, 134, 1298-1304. (26) Ji, Y.; Brueckl, T.; Baxter, R. D.; Fujiwara, Y.; Seiple, I. B.; Su, S.; Blackmond, D. G.; Baran, P. S. Innate C-H trifluoromethylation of heterocycles. Proc. Natl. Acad. Sci. USA 2011, 108, 14411-14415. (27) Wang, X.; Truesdale, L.; Yu, J.-Q. Pd(II)-catalyzed ortho-trifluoromethylation of arenes using tfa as a promoter. J. Am. Chem. Soc. 2010, 132, 3648-3649. (28) Shi, G.; Shao, C.; Pan, S.; Yu, J.; Zhang, Y. Silver-catalyzed C–H trifluoromethylation of arenes using trifluoroacetic acid as the trifluoromethylating reagent. Org. Lett. 2015, 17, 38-41. (29) Cui, L.; Matusaki, Y.; Tada, N.; Miura, T.; Uno, B.; Itoha, A. Metal-free direct C H perfluoroalkylation of arenes and heteroarenes using a photoredox organocatalyst. Adv. Synth. Catal. 2013, 355, 2203-2207. (30) Fennewald, J. C.; Lipshutz, B. H. Trifluoromethylation of heterocycles in water at room temperature. Green Chem. 2014, 16, 1097-1100. (31) Yang, Y.-D.; Iwamoto, K.; Tokunaga, E.; Shibata, N. Transition-metal-free oxidative trifluoromethylation of unsymmetricalbiaryls with trifluoromethanesulfinate. Chem. Commun. 2013, 49, 5510-5512. (32) Wang, D.; Deng, G.-J.; Chen, S.; Gong, H. Catalyst-free direct C–H trifluoromethylation of arenes in water–acetonitrile. Green Chem. 2016, 18, 5967-5970. (33) He, Z.-B.; Luo, T.; Hu, M.-Y.; Cao, Y.-J.; Hu, J.-B. Copper-catalyzed di- and trifluoromethylation of α,β-unsaturated carboxylic acids: A protocol for vinylic fluoroalkylations. Angew. Chem. Int. Ed. 2012, 51, 3944-3947. (34) Li, Z.-J.; Cui, Z.-L.; Liu, Z.-Q. Copper- and iron-catalyzed decarboxylative tri- and difluoromethylation of α,β-unsaturated carboxylic acids with CF3SO2Na and (CF2HSO2)2Zn via a radical process. Org. Lett. 2013, 15, 406-409. (35) Patra, T.; Deb, A.; Manna, S.; Sharma, U.; Maiti, D. Iron-mediated decarboxylative trifluoromethylation of α,β-unsaturated carboxylic acids with trifluoromethanesulfinate. Eur. J. Org. Chem. 2013, 5247-5250.


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(36) Yin, J.; Zhang, R.; Jin, K.; Duan, C.-Y.; Li, Y.-M. Copper/silver-mediated decarboxylative trifluoromethylation of α,β-unsaturated carboxylic acids with CF3SO2Na. Synthesis 2014, 46, 607-612. (37) Yang, L.; Jiang, L.; Li, Y.; Fu, X.; Zhang, R.; Jin, K.; Duan C. Cu(I)/Ag(I)-mediated decarboxylative trifluoromethylation of arylpropiolic acids with Me3SiCF3 at room temperature. Tetrahedron 2016, 72, 3858-3862. (38) Langlois, B. R.; Laurent, E.; Roidot, N. Trifluoromethylation of aromatic compounds with sodium trifluoromethanesulfinate under oxidative conditions. Tetrahedron Lett. 1991, 32, 75257528.


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For Table of Contents Use Only A

mild

and

practical

method

for

the

catalyst-free

decarboxylative

trifluoromethylation/perfluoroalkylation of benzoic acids by using inexpensive NaSO2CF3 as a CF3-source and solid Na2S2O8 as an initiator was described.


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Perfluoroalkylation

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