Fluoroalkylcopper(I) complexes generated by the carbocupration of tetrafluoroethylene: Construction of a tetrafluoroethylene-bridging structure

Article abstract of DOI:10.1021/ja5093776

We report a copper-mediated synthesis of a variety of 1,2-difunctionalized-1,1,2,2-tetrafluoroethylene derivatives via the carbocupration of tetrafluoroethylene. The key synthetic intermediates, 2-aryl-1,1,2,2-tetrafluoroethylcopper complexes, can be easily prepared, stored, and used as fluoroalkylation reagents. The molecular structure was unambiguously determined by X-ray crystallography and NMR analysis. We applied this method to the short-step synthesis of a liquid-crystalline compound bearing a tetrafluoroethylene-bridging structure.

Full text of DOI:10.1021/ja5093776

Communication
pubs.acs.org/JACS
Fluoroalkylcopper(I) Complexes Generated by the Carbocupration of
Tetrafluoroethylene: Construction of a Tetrafluoroethylene-Bridging
Structure
Hiroki Saijo,† Masato Ohashi,† and Sensuke Ogoshi*,†,‡
†Department of Applied Chemistry, Faculty of Engineering, Osaka University, Suita, Osaka 565-0871, Japan
‡ACT-C, Japan Science and Technology Agency (JST), Suita, Osaka 565-0871, Japan
S
* Supporting Information
Tetrafluoroethylene (TFE), which is used in the production of
ABSTRACT: We report a copper-mediated synthesis of a
variety of 1,2-difunctionalized-1,1,2,2-tetrafluoroethylene
derivatives via the carbocupration of tetrafluoroethylene.
The key synthetic intermediates, 2-aryl-1,1,2,2-tetrafluor-
oethylcopper complexes, can be easily prepared, stored,
and used as fluoroalkylation reagents. The molecular
structure was unambiguously determined by X-ray
crystallography and NMR analysis. We applied this
method to the short-step synthesis of a liquid-crystalline
compound bearing a tetrafluoroethylene-bridging struc-
ture.
PTFE and other copolymers in the fluorine industry, is one of the
ideal starting materials for the synthesis of fluorinated
compounds because it is an economical and environmentally
benign feedstock with a negligible global warming potential.11
We recently developed the transformations of TFE into
trifluorovinyl compounds by Pd(0)-catalyzed cross-coupling
reactions via C−F bond activation12a−c or by reactions using
Grignard reagents or ZnEt2 in the presence of a lithium salt.12d In
addition, TFE has the potential to be a straightforward building
block for the construction of a tetrafluoroethylene-bridging
structure (R−CF2CF2−R′), which has garnered a great deal of
attention as a key structure in liquid-crystalline compounds
because of its potential to influence the physical properties of
these materials: clearing point, mesophase sequence, and
rotational viscosity.1a,13 Tetrafluoroethylene-bridging structures
typically are constructed via the fluorination of a carbon−carbon
triple bond with F2 gas or via the deoxofluorination of 1,2-
diketones with fluorination reagents.14,15 However, these
methods have low functional group tolerance and use toxic or
costly reagents. Thus, the development of an efficient and
straightforward method has been in high demand.
rganofluorine compounds have attracted much attention
Obecause of their remarkable applications in pharmaceutical
and materials science.1 Thus, a great deal of effort has been
directed toward the development of a method for the selective
introduction of a fluorine atom into organic compounds via
reaction with a fluorination reagent such as DAST.2 In addition,
the introduction of a fluoroalkyl group is regarded as an
important approach to highly fluorinated compounds, which are
difficult to prepare using fluorination reagents.3 Since the
pioneering work by McLoughlin and Thrower in 1969, copper-
mediated fluoroalkylation has been one of the most versatile
methods for the introduction of fluoroalkyl groups.4 In the
reaction, a fluoroalkylcopper(I) complex is considered to be a
key intermediate. In 1986, Wiemers and Burton observed
[CF3Cu] species by 19F NMR analysis at low temperature.4d
Recently, isolations of ligand-stabilized fluoroalkylcopper
complexes such as [(PPh3)3CuCF3],5 [(NHC)CuCF3] (NHC
= N-heterocyclic carbene),6 and [(phen)CuCnF2n+1] (phen =
1,10-phenanthroline, n = 1−3)7 have been reported, along with
reports of outstanding performance as fluoroalkylation reagents.
In general, fluoroalkylcopper complexes are prepared via transfer
of a fluoroalkyl group from a fluoroalkyl halide, fluoroalkyl silane,
or fluoroalkane. We assumed that the 1,2-addition of organo-
copper reagents to fluoroalkenes, so-called carbocupration,8
would afford a new class of fluoroalkylcopper complexes that
would provide an important synthetic route to organofluorine
compounds that are difficult to prepare by conventional
methods. Except for highly strained cyclopropenes,9 alkenes
are not considered to be applicable to carbocupration, but
fluoroalkenes should be able to undergo carbocupration because
of their electrophilic nature.10
Herein we describe a copper-mediated transformation of TFE
into aromatic compounds bearing a tetrafluoroethylene-bridging
structure in which carbocupration of TFE is a key step (Scheme
1). Novel 2-aryl-1,1,2,2-tetrafluoroethylcopper (ATFE−Cu)
Scheme 1. Construction of a Tetrafluoroethylene-Bridging
Structure via Carbocupration of TFE
complexes generated by the carbocupration of TFE were isolated
and characterized by X-ray crystallography and NMR analysis.
With the ATFE−Cu complexes, a variety of 1,2-disubstituted-
1,1,2,2-tetrafluoroethanes were synthesized in high yields. The
short-step synthesis of a liquid-crystalline compound via
carbocupration of TFE is also described.
The carbocupration of TFE proceeded with [CuOtBu], 1,10-
phenanthroline (Phen) as the ligand, and arylboronates 1 as aryl
transfer reagents (Scheme 2). First, a phenylcopper complex
Received: September 11, 2014
© XXXX American Chemical Society
A
dx.doi.org/10.1021/ja5093776 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
The −CF2CF2(4-C6H4F) group leans to one side as a result of
the crystal packing, with one N−Cu−C angle larger than the
other [N1−Cu−C1 = 117.43(11)°, N2−Cu−C1 =
161.65(11)°] and one N−Cu distance longer than the other
[N1−Cu = 2.157(3) Å, N2−Cu = 1.981(2) Å].
Scheme 2. Synthesis of ATFE−Cu Complexes 3
NMR analysis (Figure 1c) showed that in solution 3b exists as
a mixture of a neutral form, [(phen)CuCF2CF2(4-C6H4F)] (3b-
n), and an ionic form, [(phen)2Cu][Cu(CF2CF2(4-C6H4F))2]
(3b-i). In the 19F NMR spectrum of 3b in THF-d8, broad signals
assigned to 3b-n were observed at −110.4, −112.0 (for
−CF2CF2−), and −120.1 ppm (for Ar−F). Those assigned to
3b-i were observed at −115.0, −118.3, and −120.3 ppm. The 3b-
n:3b-i peak-area ratio was ca. 5:2 but depended on the
concentration of 3b and the polarity of the solvent. The dynamic
behavior of 3b in solution is consistent with previous studies of
fluoroalkylcopper complexes.6,7,18
Although organoboron compounds are less common in the
preparation of organocopper reagents,19 their use confers great
advantages with regard to ease of handling and functional group
tolerance. Furthermore, the weak Lewis acidic nature of both 1
and 2-tert-butoxy-5,5-dimethyl-1,3,2-dioxaborinane is quite
important for the synthesis of 3 because Lewis acidic species
can cause decomposition of the complex through α- or β-fluorine
elimination. In fact, the reaction using phenylmagnesium
bromide instead of 1a did not produce 3a at all, and
trifluorostyrene (4) was obtained in 70% yield as a result of β-
fluorine elimination. Moreover, 3a was immediately converted
into 4 by treatment with magnesium bromide at room
temperature. We assumed that the Lewis acidic metal species
were involved in the β-fluorine elimination step through
interaction with a fluorine atom. Although organoboron
compounds also have a potential Lewis acidic nature, their
Lewis acidity might be very low to avoid the β-fluorine
elimination during the synthesis of 3.
[(phen)CuPh] (2a)16 was prepared by the reaction of 5,5-
dimethyl-2-phenyl-1,3,2-dioxaborinane (1a), [CuOtBu], and
Phen in tetrahydrofuran (THF). The reaction was completed
within 10 min at room temperature, and the quantitative
formation of 2a and 2-tert-butoxy-5,5-dimethyl-1,3,2-dioxabor-
1
inane was confirmed by H and 11B NMR analysis. Then the
THF solution of 2a was exposed to TFE (3.5 atm) and heated at
40 °C for 24 h. After the removal of TFE and THF under reduced
pressure, the resultant solid was washed with ether to give the
ATFE−Cu complex [(phen)CuCF2CF2Ph] (3a) in 88% yield as
a brown solid (1.86 g, 4.43 mmol). This is the first example of the
preparation of a fluoroalkylcopper complex via carbocupration of
a fluoroalkene.17 It is worth noting that 3a was stable under N2 at
room temperature and could be stored for at least a few months
without decomposition. An analogous complex bearing a fluorine
substituent at the 4-position, [(phen)CuCF2CF2(4-C6H4F)]
(3b), was also prepared in 89% yield. 19F NMR monitoring
indicated that the transformation of 1b into 3b proceeded
through complex 2b (Figure 1).
Next, we investigated the reactivity of 3a (Scheme 3). As
mentioned above, treatment of 3a with magnesium bromide
Scheme 3. Transformations of 3a
Figure 1. 19F NMR spectra (in THF-d8) of (a) 1b, (b) 2b, and (c) 3b.
The molecular structure of 3b was determined by X-ray
crystallography (Figure 2). A single crystal suitable for X-ray
afforded 4 via β-fluorine elimination. Iodonolysis of 3a at room
temperature gave (1,1,2,2-tetrafluoro-2-iodoethyl)benzene (5)
in 81% yield. A phosphine compound bearing a fluoroalkyl group
(6) was obtained by the reaction of 3a with PPh2Cl. Moreover,
the reaction of 3a with benzyl chloroformate generated a C−C
bond to give the corresponding ester 7 in 89% yield, and
subsequent hydrogenation catalyzed by 10% Pd/C afforded the
corresponding carboxylic acid 8 quantitatively.
Figure 2. ORTEP structure of 3b with thermal ellipsoids at the 30%
probability level. H atoms have been omitted for clarity.
Furthermore, the ATFE−Cu complex was also applicable for
the coupling reaction with iodoarenes 9 to give 1,2-diaryl-1,1,2,2-
tetrafluoroethanes 10 (Table 1). After the preliminary screening
of the reaction conditions, we found that the reaction of
iodobenzene (9a) with 1.2 equiv of 3a in THF proceeded at 60
°C to afford 1,1,2,2-tetrafluoro-1,2-diphenylethane (10aa) in
98% yield. Under the reaction conditions, electron-deficient 4-
iodobenzotrifluoride (9b) reacted with 3a smoothly to give 10ab
diffraction analysis was obtained by recrystallization from a
saturated solution of 3b in THF at room temperature. The
revealed monomeric structure clearly shows the formation of
Cu−C and C−C bonds. The sum of the three bond angles
around the Cu atom is 359.78°. Thus, Cu, C1, N1, and N2 are in
the same plane, and 3b has a trigonal-planar molecular geometry.
B
dx.doi.org/10.1021/ja5093776 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
a
Various substituted arylboronates were converted into 1,2-
diaryl-1,1,2,2-tetrafluoroethanes 10 (Table 2). Fluorine, chlor-
Table 1. Substrate Scope of Iodoarenes
a
Table 2. Substrate Scope of the One-Pot Synthesis of 10
a
b
Isolated yields are shown. Heated at 40 °C for 48 h before the
addition of 9b to complete the formation of 3.
a
b
Isolated yields are shown. Conducted with 3a (0.30 mmol) and 9m
ine, and bromine substituents were tolerated in the reaction
(10bb−db). The reactions using electron-rich arylboronates
proceeded to give the products in high yields (10eb−gb). The
carbocupration reactions with electron-deficient arylboronates
were relatively sluggish and required longer reaction times in
order to complete the formation of the ATFE−Cu intermediates,
which reacted with 9b to give the corresponding coupling
products 10hb−jb. An arylboronate bearing a vinyl group and
sterically hindered 1-naphthylboronate were also applicable to
the carbocupration of TFE (10kb and 10lb).
c
(1.50 mmol). Conducted with 3a (0.72 mmol) and 9m (0.30 mmol).
d
Conducted with 9p instead of the corresponding iodide.
in 97% yield. The reactions with electron-rich 4-iodoanisole (9c)
and sterically hindered iodomesitylene (9d) were sluggish, but
the corresponding coupling products 10ac and 10ad were
obtained in high yields. Functional groups such as formyl, ester,
and cyano were tolerant of the reaction conditions (10ae−ag).
Substrates bearing a C−C triple bond or a boronate, phosphate,
amino, bromo, or chloro group were converted to the
corresponding products (10ah−al), which are potential
substrates for further functionalization by, for example,
Suzuki−Miyaura or Horner−Wadsworth−Emmons reaction.
In addition, 1,4-diiodobenzene (9m) was selectively converted
to either the mono- or disubstituted product depending on the
stoichiometric proportions: the reaction using excess 9m relative
to 3a gave the monosubstituted product (10am) in 71% yield,
and that using excess 3a relative to 9m gave the disubstituted
product (10am′) in 67% yield. We found that 2-iodopyridine
(9n) and alkenyl iodide (9o) also reacted with 3a to give the
products 10an and 10ao in excellent yields. The coupling
reaction of 3a with bromobenzene did not occur, but electron-
deficient 4-bromophthalic anhydride (9p) reacted with 3a to
afford the corresponding coupling product 10ap.
In addition to the above-mentioned stepwise reaction using
3a, we conducted a one-pot synthesis of 1,2-diaryl-1,1,2,2-
tetrafluoroethanes 10 from 1, TFE, and 9 without isolation of the
corresponding ATFE−Cu complexes. First, 2a was generated in
situ by the reaction of 1a, [CuOtBu], and Phen, and the resultant
solution was transferred to an autoclave reactor. TFE (3.5 atm)
was charged into the reactor, and the reaction mixture was heated
at 40 °C for 24 h. After the removal of TFE under reduced
pressure, the reaction mixture was heated with a small excess
amount of 9b at 60 °C for 4 h. The target compound 10ab was
isolated in 92% yield after separation by silica gel column
chromatography. In the one-pot reaction, no significant side
product was obtained. On the other hand, when all of the starting
materials, including 9b, were mixed at once before the heating, a
complicated mixture was obtained, and 10ab was observed in
only 15% yield by 19F NMR spectroscopy.20
Finally, we applied the present method to the synthesis of a
liquid-crystalline compound bearing a tetrafluoroethylene-
bridging structure. Materials containing the tetrafluoroethy-
lene-bridging structure are expected to be used in the next
generation of active-matrix liquid crystal displays with reduced
power consumption, and the development of an efficient and
convenient synthetic method has been in high demand. A
previous report13d detailed the synthesis of a liquid-crystalline
compound bearing a tetrafluoroethylene-bridging structure in 10
steps from 4,4′-(tetrafluoroethane-1,2-diyl)diphenol bearing the
tetrafluoroethylene-bridging structure.21 By contrast, through
carbocupration of TFE, 17 was synthesized in six steps from
commercially available 4-pentylphenylboronic acid (11)
(Scheme 4). Even though 17 was obtained as a mixture of
geometric isomers, each of the isomers was separated by means
of preparative HPLC. ATFE−Cu complex 13, which is a key
intermediate in this transformation, could be prepared and
stored at room temperature under N2 in a manner similar to 3a.
In conclusion, we have demonstrated the synthesis, character-
ization, and synthetic application of 2-aryl-1,1,2,2-tetrafluoroe-
thylcopper complexes, which are generated by the carbocupra-
tion of tetrafluoroethylene. The molecular structure was
unambiguously determined by X-ray crystallography and NMR
analysis. Using the complexes as fluoroalkylation reagents, we
synthesized a variety of 1,2-difunctionalized-1,1,2,2-tetrafluoro-
ethanes in high yields. The synthetic utility of this method was
demonstrated by the short-step synthesis of a liquid-crystalline
compound bearing a tetrafluoroethylene-bridging structure.
C
dx.doi.org/10.1021/ja5093776 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
a
Martin, E.; Grushin, V. V. Angew. Chem., Int. Ed. 2013, 52, 11637.
Scheme 4. Synthesis of Liquid-Crystalline Compound 17
(m) Lishchynskyi, A.; Novikov, M. A.; Martin, E.; Escudero-Adan
Novak, P.; Grushin, V. V. J. Org. Chem. 2013, 78, 11126. (n) Serizawa,
H.; Aikawa, K.; Mikami, K. Chem.Eur. J. 2013, 19, 17692.
(5) (a) Usui, Y.; Noma, J.; Hirano, M.; Komiya, S. Inorg. Chim. Acta
2000, 309, 151. (b) Tomashenko, O. A.; Escudero-Adan, E. C.;
Belmonte, M. M.; Grushin, V. V. Angew. Chem., Int. Ed. 2011, 50, 7655.
(c) Larsson, J. M.; Pathipati, S. R.; Szabo, K. J. J. Org. Chem. 2013, 78,
7330.
́
, E. C.;
́
́
́
(6) (a) Dubinina, G. G.; Furutachi, H.; Vicic, D. A. J. Am. Chem. Soc.
2008, 130, 8600. (b) Dubinina, G. G.; Ogikubo, J.; Vicic, D. A.
Organometallics 2008, 27, 6233.
(7) (a) Morimoto, H.; Tsubogo, T.; Litvinas, N. D.; Hartwig, J. F.
Angew. Chem., Int. Ed. 2011, 50, 3793. (b) Litvinas, N. D.; Fier, P. S.;
Hartwig, J. F. Angew. Chem., Int. Ed. 2012, 51, 536. (c) Mormino, M. G.;
Fier, P. S.; Hartwig, J. F. Org. Lett. 2014, 16, 1744. (d) Oishi, M.; Kondo,
H.; Amii, H. Chem. Commun. 2009, 1909. (e) Weng, Z.; Lee, R.; Jia, W.;
Yuan, Y.; Wang, W.; Feng, X.; Huang, K.-W. Organometallics 2011, 30,
3299.
a
Reagents and conditions: (a) 2,2-dimethyl-1,3-propanediol, toluene,
reflux, 10 h; (b) [CuOtBu], Phen, TFE, THF, 40 °C, 5 h; (c) 4-
(CO2Et)C6H4I, THF, 60 °C, 4 h; (d) KOH, MeOH/H2O, 60 °C, 12
h; (e) H2, cat. Rh/Al, AcOH, 60 °C, 12 h; (f) 3,4,5-trifluorophenol,
DCC, DMAP, CH2Cl2, rt, 24 h.
(8) (a) Krause, N. Modern Organocopper Chemistry; Wiley-VCH:
Weinheim, Germany, 2002. (b) Normant, J. F.; Alexakis, A. Synthesis
1981, 841. (c) Marek, I. J. Chem. Soc., Perkin. Trans. 1 1999, 535.
(d) Shimizu, Y.; Kanai, M. Tetrahedron Lett. 2014, 55, 3727.
(9) Nakamura, E.; Isaka, M.; Matsuzawa, S. J. Am. Chem. Soc. 1988, 110,
1297.
(10) Examples of addition−elimination reactions of TFE with
organometallic reagents: (a) Dixon, S. J. Org. Chem. 1956, 21, 400.
(b) Simmons, H. E. J. Am. Chem. Soc. 1961, 83, 1657. (c) Crouse, G. D.;
Webster, J. D. J. Org. Chem. 1992, 57, 6643.
(11) Acerboni, G.; Beukes, J. A.; Jensen, N. R.; Hjorth, J.; Myhre, G.;
Nielsen, C. J.; Sundet, J. K. Atmos. Environ. 2001, 35, 4113.
(12) (a) Ohashi, M.; Kambara, T.; Hatanaka, T.; Saijo, H.; Doi, R.;
Ogoshi, S. J. Am. Chem. Soc. 2011, 133, 3256. (b) Ohashi, M.; Saijo, H.;
Shibata, M.; Ogoshi, S. Eur. J. Org. Chem. 2013, 443. (c) Ohashi, M.;
Kamura, R.; Doi, R.; Ogoshi, S. Chem. Lett. 2013, 42, 933. (d) Saijo, H.;
Sakaguchi, H.; Ohashi, M.; Ogoshi, S. Organometallics 2014, 33, 3669.
(13) (a) Kirsch, P.; Bremer, M.; Huber, F.; Lannert, H.; Ruhl, A.; Lieb,
M.; Wallmichrath, T. J. Am. Chem. Soc. 2001, 123, 5414. (b) Kirsch, P.;
Huber, F.; Lenges, M.; Taugerbeck, A. J. Fluorine Chem. 2001, 112, 69.
(c) Kirsch, P.; Bremer, M. ChemPhysChem 2010, 11, 357. (d) Kirsch, P.;
Huber, F.; Krause, J.; Heckmeier, M.; Pauluth, D. U.S. Patent
20030230737 A1, December 2003.
ASSOCIATED CONTENT
* Supporting Information
Procedures and analytical and spectral data. This material is
available free of charge via the Internet at http://pubs.acs.org.
■
S
AUTHOR INFORMATION
Corresponding Author
ogoshi@chem.eng.osaka-u.ac.jp
Notes
■
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was partially supported by a Grant-in-Aid for Scientific
Research (A) (21245028), a Grant-in-Aid for Young Scientist
(A) (25708018), and a Grant-in-Aid for Scientific Research on
Innovative Areas “Molecular Activation Directed toward
Straightforward Synthesis” (23105546) from MEXT and by
Adaptable and Seamless Technology Transfer Program through
target-driven R&D (A-STEP) (AS2525804M) from JST. We
express our thanks to Daikin Industries, Ltd., for supplying TFE.
M.O. also acknowledges The Noguchi Institute.
(14) Gatenyo, J.; Rozen, S. J. Fluorine Chem. 2009, 130, 332 and
references therein.
(15) Chang, Y.; Tewari, A.; Adi, A.-I.; Bae, C. Tetrahedron 2008, 64,
9837 and references therein.
(16) Camus, A.; Marsich, N. J. Organomet. Chem. 1970, 21, 249.
(17) A few 1,4-addition reactions of organocuprates with fluorinated
enones had been reported, but no fluoroalkylcopper complex had been
REFERENCES
■
(1) (a) Kirsch, P. Modern Fluoroorganic Chemistry: Synthesis, Reactivity,
Applications, 2nd ed.; Wiley-VCH: Weinheim, Germany, 2013.
(b) Wang, J.; Sanchez-Rosello, M.; Acena, J. L.; del Pozo, C.;
́
́
̃
̂
obtained. See: (a) Gillet, J. P.; Sauvetre, R.; Normant, J. F. Synthesis
Sorochinsky, A. E.; Fustero, S.; Soloshonok, V. A.; Liu, H. Chem. Rev.
2014, 114, 2432.
1982, 297. (b) Ichikawa, J.; Yokota, N.; Kobayashi, M.; Minami, T.
Synlett 1993, 186. (c) Yamada, S.; Shimoji, K.; Takahashi, T.; Konno, T.;
Ishihara, T. J. Fluorine Chem. 2013, 149, 95 and references therein.
(18) For related reports on the dynamic behavior of ligated copper(I)
amidates, see: (a) Tye, J. W.; Weng, Z.; Johns, A. M.; Incarvito, C. D.;
Hartwig, J. F. J. Am. Chem. Soc. 2008, 130, 9971. (b) Strieter, E. R.;
Bhayana, B.; Buchwald, S. L. J. Am. Chem. Soc. 2009, 131, 78.
(19) Recent examples: (a) Takashi, K.; Shintani, R.; Hayashi, T. Angew.
Chem., Int. Ed. 2011, 50, 5548. (b) Rucker, R. P.; Whittaker, A. M.; Dang,
H.; Lalic, G. Angew. Chem., Int. Ed. 2012, 51, 3953. (c) Zhou, Y.; You,
W.; Smith, K. B.; Brown, M. K. Angew. Chem., Int. Ed. 2014, 53, 3475.
(20) Attempts to reduce Cu(I) species to catalytic amounts were
unsuccessful. In the presence of catalytic amount of CuI and Phen, the
reaction of 1a, 5a, TFE, and KOtBu afforded a complicated mixture
including 4, which was generated through the β-fluorine elimination.
(21) For a patent on the synthesis of 4,4′-(perfluoroethane-1,2-diyl)
diphenol, see: Albrecht, M.; Kathe, B. U.S. Patent 20030009060 A1,
January 2003.
(2) (a) Al-Maharik, N.; O’Hagan, D. Aldrichimica Acta 2011, 44, 65.
(b) Furuya, T.; Klein, J. E. M. N.; Ritter, T. Synthesis 2010, 1804.
(3) (a) Furuya, T.; Kamlet, A. S.; Ritter, T. Nature 2011, 473, 470.
(b) Liang, T.; Neumann, C. N.; Ritter, T. Angew. Chem., Int. Ed. 2013,
52, 8214. (c) Burton, D. J.; Yang, Z.-Y. Tetrahedron 1992, 48, 189.
(4) (a) McLoughlin, V. C. R.; Thrower, J. Tetrahedron 1969, 25, 5921.
(b) Kobayashi, Y.; Kumadaki, I. Tetrahedron Lett. 1969, 10, 4095.
(c) Oishi, M.; Kondo, H.; Amii, H. Chem. Commun. 2009, 1909.
(d) Wiemers, D. M.; Burton, D. J. J. Am. Chem. Soc. 1986, 108, 832.
(e) Yang, Z.-Y.; Wiemers, D. M.; Burton, D. J. J. Am. Chem. Soc. 1992,
114, 4402. (f) Yang, Z.-Y.; Burton, D. J. J. Fluorine Chem. 2000, 102, 89.
́
(g) Folleas, B.; Marek, I.; Normant, J.-F.; Saint-Jalmes, L. Tetrahedron
2000, 56, 275. (h) Zanardi, A.; Novikov, M. A.; Martin, E.; Benet-
Buchholz, J.; Grushin, V. V. J. Am. Chem. Soc. 2011, 133, 20901.
(i) Novak
2012, 51, 7767. (j) Novak
Chem. Soc. 2012, 134, 16167. (k) Lishchynskyi, A.; Grushin, V. V. J. Am.
́
, P.; Lishchynskyi, A.; Grushin, V. V. Angew. Chem., Int. Ed.
, P.; Lishchynskyi, A.; Grushin, V. V. J. Am.
́
Chem. Soc. 2013, 135, 12584. (l) Konovalov, A. I.; Benet-Buchholz, J.;
D
dx.doi.org/10.1021/ja5093776 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX