Expedient synthesis of tetrafluorophenoxthiines and derivatives by copper(I)-catalyzed cross-coupling reaction

Article abstract of DOI:10.1016/j.jfluchem.2013.05.023

In this research, tetrafluorophenoxthiines were successfully synthesized from pentafluorobenzene and aryl thiols or diaryl disulfides in the presence of copper catalyst and ligand by using O2 as the oxidant, t-BuOLi as the base at 100 8C. The ligand (E)-3-(dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one (L) played an indispensable role in the reaction. This work contains a notable mode of C-F bond activation, which is in the ortho position to the C-H bond of pentafluorobenzene.

Full text of DOI:10.1016/j.jfluchem.2013.05.023

Journal of Fluorine Chemistry 153 (2013) 33–38
Contents lists available at SciVerse ScienceDirect
Journal of Fluorine Chemistry
journal homepage: www.elsevier.com/locate/fluor
Expedient synthesis of tetrafluorophenoxthiines and derivatives by
copper(I)-catalyzed cross-coupling reaction
Chuanming Yu, Gaobo Hu, Cuiling Zhang, Ran Wu, Haiwei Ye, Guanghui Yang,
*
Xiangjun Shi
Key Laboratory for Green Pharmaceutical Technologies and Related Equipment of Ministry of Education, College of Pharmaceutical Sciences, Zhejiang
University of Technology, Hangzhou 310014, PR China
A R T I C L E I N F O
A B S T R A C T
Article history:
In this research, tetrafluorophenoxthiines were successfully synthesized from pentafluorobenzene and
aryl thiols or diaryl disulfides in the presence of copper catalyst and ligand by using O2 as the oxidant, t-
BuOLi as the base at 100 8C. The ligand (E)-3-(dimethylamino)-1-(2-hydroxyphenyl)prop-2-en-1-one (L)
played an indispensable role in the reaction. This work contains a notable mode of C–F bond activation,
which is in the ortho position to the C–H bond of pentafluorobenzene.
Received 15 March 2013
Received in revised form 10 May 2013
Accepted 24 May 2013
Available online 11 June 2013
ß 2013 Elsevier B.V. All rights reserved.
Keywords:
Copper-catalyzed
Tetrafluorophenoxthiines
Cross-coupling
Pentafluorobenzene
C–H/C–F activation
1. Introduction
Xu [10] described a ligand (E)-3-(dimethylamino)-1-(2-hydro-
xyphenyl)prop-2-en-1-one (L) for hydroxylation reaction of arenes
The importance of fluorinated arenes and derivatives have been
demonstrated by their application in pharmaceuticals [1] and
material science [2]. In the past decades, a variety of methods to
prepare these useful compounds have been developed. Recently,
polyfluoroarenes with alkynes [3], alkenes [4], heterocycles [5],
and simple arenes [6], have been reported. Transition-metal-
catalyzed C–S bond formation of pentafluorobenzene with aryl
thiols was also discovered in our laboratory [7]. The formation of
C–S bond, fundamental to the art of organic synthesis, represents a
key step to the synthesis of a broad range of biologically important
molecules [8].
Motivated by the above significance, we focused our attention
on the copper-catalyzed C–H bond transformation of pentafluor-
obrnzene. Zhao et al. and Schaub et al. [9] reported that both the C–
H bond and the C–F bond (in the para position to the C–H bond)
could easily be activated. It was proved in our precious work that
the C–S products, like monoarylthiolation 5a and bisarylthiolation
4a, could be obtained in the reaction between pentafluorobrnzene
and thiophenol with DDQ (Scheme 1, Eq. (1)) [7]. Interestingly, the
reaction would give tetrafluorophenoxthiines 3a, a new product,
without the addition of DDQ (Scheme 1, Eqs. (2) and (3)).
at a position activated by an adjacent S group. With this ligand in
hand, we present the first example of pentafluorobenzene (1) with
thiols (2) or diaryl disulfides (6) for the formation of S, O-
heterocycles via C–H and its adjacent C–F bond activation of 1.
2. Results and discussion
In our initial experiments pentafluorobenzene (1) with
thiophenol (2a) were chosen as model substrates for exploring
the optimum reaction conditions. These results are shown in
Table 1. To our delight, the product 3a was detectable and easily
isolated. The structure was confirmed by 1H NMR, 13C NMR, 19F
NMR, MS (EI), and HRMS.
On the basis of our previous work [7], the reaction was
catalyzed by CuBr (30 mol%) and L (30 mol%) in the presence of t-
BuOLi (2 equiv.) as the base in DMSO at 60 8C under an atmosphere
of O2 (1 atm), but the expected product 3a was only isolated in 22%,
and 4a in 25% (Table 1, entry 1). Higher temperature was
speculated to be required. Under otherwise identical conditions,
the optimum reaction temperature was achieved at 100 8C
(Table 1, entries 2–4). To further improve the yields in this
transformation, the effect of base was systematically examined. It
was found that t-BuOLi gave the best results (Table 1, entry 3).
Whereas other bases, such as K3PO4 K2CO3, Cs2CO3, t-BuONa were
less effective in this reaction (Table 1, entries 5–8). Next, a variety
* Corresponding author. Tel.: +86 571 8832075; fax: +86 571 8832075.
E-mail address: shixj@zjut.edu.cn (X. Shi).
0022-1139/$ – see front matter ß 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jfluchem.2013.05.023

34
C. Yu et al. / Journal of Fluorine Chemistry 153 (2013) 33–38
Previous work:
F
F
F
F
H
F
SH
F
S
S
F
F
F
S
F
Cu salt, Base
+
+
F
F
phen.H2O, DDQ
F
F
(1)
1
2a
5a
4a
This work:
F
F
F
F
F
H
F
SH
F
F
S
F
S
F
Cu salt, Base
+
+
F
F
L
, without DDQ
O
S
F
(2)
1
2a
3a
4a
F
F
F
F
F
S
F
Cu salt, Base
H
F
F
F
S
S
+
+
S
S
L
, without DDQ
F
F
O
F
F
1
6a
3a
4a
(3)
Scheme 1. Synthesis of tetrafluorophenoxthiines.
Table 1
Optimization of the model reaction.a
Entry
Cu salt
Base
Solvent
Temp (8C)
3ac (%)
4a (%)
1
2
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuI
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
K3PO4
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMSO
DMF
60
80
22d
28
36
32
32
26
23
trace
33
30
31
28
19
27
0
25
35
37
34
33
29
31
27
34
32
35
30
33
32
0
3
100
120
100
100
100
100
100
100
100
100
100
100
100
4
5
6
K2CO3
7
Cs2CO3
t-BuONa
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
t-BuOLi
8
9
10
11
12
13
14
15
CuCl
CuBr2
Cu(OTf)2
CuBr
CuBr
CuBr
DMA
NMP
a
Unless otherwise noted, reaction conditions were 1 (2.5 mmol), 2a (1 mmol), Cu salt (30 mol%), L (30 mol%), base (2 equiv.), solvent (4 ml), protected by O2 for 8 h.
b
L:
.
c
Isolated yield.
d
Reaction time 24 h.
of copper salts were tested, CuBr was proved to be more active than
compatible on the aryl thiols, leading the moderate yields of
corresponding products 3b-l and 4b-l (Table 2, entries 2–12). In
addition, to our surprise, we found that 2-fluorothiophenol 2h,
which afforded the products 3a and 4a rather than 3h and 4h
(Table 2, entry 8). It may due to the competing reactions between
the activated C–F and C–H bonds lying at the ortho position to the S
atom, while the C–F bonds have superiority in activation [11].
When the aryl thiols with an electron-donating group (Table 2,
entry 3) in the meta position to the S atom, the O atom of 3c was
lie para to the CH3, while the O atom of 3i and 3j was lie ortho to
other Cu sources, furnishing 3a in 36% and 4a in 37% (Table 1,
entries 3, 9–12). After that, the solvent was examined, and results
showed that DMSO gave a higher yield (Table 1, entry 3) than DMF
and DMA (Table 1, entries 13–14), while NMP was ineffective for
this reaction (Table 1, entry 15).
The scope of reaction was further investigated, a wide array of
thiophenols 2 have been tested, and the results were summarized
in Table 2. Both electron-donating (Table 2, entries 2–7) and
electron-withdrawing substituents (Table 2, entries 8–12) were

C. Yu et al. / Journal of Fluorine Chemistry 153 (2013) 33–38
35
Table 2
Substrate scope of aryl thiols.a
.
Entry
R
Products yieldb (%)
1
2
H (2a)
(3a) 36
(3b) 28
(3c) 28
(3d) 30
(3e) 36
(3f) 29
(3g) 28
(3a) 31
(3i) 24
(3j) 26
(3k) 20
(3l) 30
(4a) 37
(4b) 40
(4c) 35
2-CH3 (2b)
3-CH3 (2c)
2-OCH3 (2d)
4-OCH3 (2e)
4-CH(CH3)2 (2f)
2,4-(CH3)2 (2g)
2-F (2h)
3
4
(4d) trace
(4e) 39
(4f) 37
5
6
7
(4g) 33
(4a) 29
(4i) 37
8c
9
3-F (2i)
10
11
12
3-Br (2j)
(4j) trace
(4k) trace
(4l) 30
4-Br (2k)
4-Cl (2l)
a
Reaction conditions: 2 (1.0 mmol), 1 (2.5 mmol), CuBr (30 mol%), L (30 mol%), t-BuOLi (2 equiv.), DMSO (4 mL) at 100 8C under an atmosphere of oxygen for 8 h.
Isolated yield base on 2.
3h:
b
c
4h:
.
Table 3
Substrate scope of diaryl disulfides.a
.
Entry
R
Products yieldb (%)
1
2
3
4
5
6
7
8
9
H (6a)
(3a) 27
(3b) 30
(3e) 35
(3f) 34
(3a) 31
(3i) 27
(3j) 25
(3k) 33
(3l) 35
(4a) 48
(4b) 38
(4e) 39
(4f) 36
2-CH3 (6b)
4-OCH3 (6e)
4-CH(CH3)2 (6f)
2-F (6h)
(4a) 37
(4i) 27
3-F (6i)
3-Br (6j)
(4j) trace
(4k) trace
(4l) 39
4-Br (6k)
4-Cl (6l)
a
Reaction conditions: 6 (0.5 mmol), 1 (2.5 mmol), CuBr (30 mol%), L (30 mol%), t-BuOLi (2 equiv.), DMSO (4 mL) at 100 8C under an atmosphere of oxygen for 8 h.
Isolated yield base on 6.
b
the F or Br, When the aryl thiols with an electron-withdrawing
group (Table 2, entries 9 and 10) in the meta position to the S
atom. It is speculated that preferential attack on the 2- or 6-
position is rationalized by considering the thiol and methyl,
ortho-para directing groups in the structure of 3-methylbenze-
nethiol; and 2-position is relatively low activity owing to the
sterically hindered effect (Fig. 1), which leading to the para-
position relationship between oxygen atom and methyl group in
the products. When the meta-position atom of benzenethiol
change into chlorine or bromine, which are also ortho-para
directing halogen groups, the cloud density of benzene ring
Fig. 1. Selectivity of electron-donating and electron-withdrawing group.

36
C. Yu et al. / Journal of Fluorine Chemistry 153 (2013) 33–38
the aromatic ring [10a] generates pentafluorobenzenecopper
species E, which underwent C–F activation at the C-2 position
and affords product 3a and complex A after reductive elimination
to finish the catalytic cycle. In addition, activation of C–H and C–F
bond of 1, reacts with transition-state B to form species D. Finally,
reductive elimination of D to gave compound 4a and A.
3. Conclusion
In summary, we have developed an unprecedented cross-
coupling reaction of pentafluorobenzene with aryl thiols or diaryl
disulfides, providing an efficient method to build up S, O-
heterocycles. The process is simple and efficient under mild
conditions. Further studies are underway in our laboratory.
4. Experimental
Scheme 2. Preliminary mechanistic studies.
4.1. General information
would be reduced however; and maybe more intensely at para-
position relative to ortho-position (Fig. 1). As a result, oxygen
atom in the product has a ortho-position relationship with
halogen group.
Analytical grade solvents and commercially available reagents
were used without further purification. Melting points were
determined on a Bu¨chi B-540 capillary melting point apparatus
and uncorrected. 1H NMR and 13C NMR spectra were recorded at
VARAIN-400 using CDCl3 as the solvent, and chemical shifts are
expressed in parts per million (ppm) by using TMS as an internal
standard. Mass spectra were measured with a Finnigan Trace DSQ
instrument or a GCT Premier mass spectrometer. High-resolution
mass spectral (HRMS) analyses were measured with an APEX
(Bruker) mass III spectrometer or GC Premier mass spectrometer
by using ESI or EI techniques. Silica gel for column chromatography
was purchased from Qingdao Haiyang Chemical Co., Lt. All yields
described herein are the isolated yields after column chromatog-
raphy.
As
a further aspect, several diaryl disulfides were also
investingated. As illustrated in Table 3, the substrates 6 containing
electron-rich (Table 3, entries 2–4) and electron-deficient (Table 3,
entries 5–9) group would give products in good yields.
To probe the mechanism of this transformation, a series of
controlled experiments were further conducted (as shown in
Scheme 2). No reaction occurred when O2 was replaced by N2, this
result indicate that oxidation of O2 was necessary in the
transformation. Furthermore, under the optimum reaction condi-
tions, 5a did not afford the desired product 3a, which illustrates
that 5a could not be formed in the reaction process.
On the basis of the preliminary studies, the catalytic cycle was
proposed as shown in Scheme 3. The initial step involves the
deprotonation of 2a, and then reacts with complex A to provide
intermediate B [7,12]. Then the copper (I) is oxidized by dioxygen
to form the more active complex C [13]. Selective hydroxylation of
4.2. General procedure for the reaction
CuBr (0.043 g, 30 mol%), L (0.057 g, 30 mol%), t-BuOLi (0.16 g,
2 equiv.) were placed in DMSO (4 mL). The mixture was stirred at
Scheme 3. Proposed mechanism for direct transformation.

C. Yu et al. / Journal of Fluorine Chemistry 153 (2013) 33–38
37
room temperature for 10 min. Then 2 (1 mmol) or 6 (0.5 mmol)
was added and the reaction flask was evacuated and refilled with
O2 three times, stirred for 10 min at RT. Pentafluorobenzene 1
(0.42 g, 2.5 mmol) was added in turn to the flask using syringes.
The reaction mixture was stirred at 100 8C under an atmosphere of
oxygen for 8 h. After cooling down, the reaction mixture was
diluted with 20 mL of ethyl ether, filtered through a pad of silica
gel, followed by washing the pad of the silica gel with the same
solvent (20 mL). The filtrate was washed with water (3 Â 15 mL).
The organic phase was dried over anhydrous Na2SO4, filtered,
concentrated under reduced pressure. The residue was then
purified by flash chromatography on silica gel to provide the
corresponding product.
J1 = 18.8 Hz, J2 = 7.5 Hz, 1F), À163.04 (t, J = 22.6 Hz, 1F); MS
(EI):314; HRMS calcd for C15H10F4OS: 314.0388, found: 314.0387.
4.2.7. Compound 3g
White solid; mp 105.7–108.3 8C; 1H NMR (400 MHz, CDCl3):
d
d
6.77–6.76 (s, 2H), 2.27–2.26 (s, 6H); 13C NMR (100 MHz, CDCl3):
149.9, 143.2, 140.9, 139.2, 138.4, 138.0, 136.6, 135.9, 135.2, 127.5,
116.2, 20.6, 19.3; 19F NMR (376 MHz, CDCl3):
d
À141.51 (m, 1F),
À158.30 (m, 1F), À159.42 (m, 1F), À163.35 (m, 1F); MS (EI): 300;
HRMS calcd for C14H8F4OS: 300.0232, found: 300.0231.
4.2.8. Compound 3i
White solid; mp 60.3–62.8 8C; 1H NMR (400 MHz, CDCl3):
d
7.01
(dd, J1 = 8.0 Hz, J2 = 4.0 Hz, 1H), 6.86–6.81 (m, 2H); 13C NMR
(100 MHz, CDCl3): 160.7, 158.2, 146.4, 143.3, 141.0, 139.3, 138.7,
136.7, 136.2, 119.1, 115.2, 113.7; 19F NMR (376 MHz, CDCl3):
4.2.1. Compound 3a
d
White solid; mp 72.5–74.5 8C; 1H NMR (400 MHz, CDCl3):
d
d
7.22–7.18 (m, 1H), 7.14–7.08 (m, 3H); 13C NMR (100 MHz, CDCl3):
150.3, 143.2, 140.9, 139.3, 138.5, 136.4, 128.6, 126.9, 125.6,
118.1, 116.4, 106.9; 19F NMR (376 MHz, CDCl3):
À116.53 (m, 1F), À140.88 (dd, J1 = 22.6 Hz, J2 = 7.5 Hz, 1F), À157.08
(t, J = 18.8 Hz, 1F), À158.55 (dd, J1 = 22.6 Hz, J2 = 7.5 Hz, 1F),
À162.23 (t, J = 22.6 Hz, 1F); MS (EI): 290; HRMS calcd for
d
d
À141.27 (m, 1F),
À157.89 (t, J = 18.8 Hz, 1F), À158.88 (m, 1F), À162.79 (m, 1F); MS
C12H3F5OS: 289.9825, found: 289.9821.
(EI): 272; HRMS calcd for C12H4F4OS: 271.9919, found: 271.9920.
4.2.9. Compound 3j
4.2.2. Compound 3b
White solid; mp 98.7–100.4 8C; 1H NMR (400 MHz, CDCl3):
d
White solid; mp 129.6–132.0 8C; 1H NMR (400 MHz, CDCl3):
d
7.24 (dd, J1 = 8.0 Hz, J2 = 4.0 Hz, 1H), 7.20 (d, J = 8.0 Hz 1H), 6.91 (d,
J = 8.0 Hz 1H); 13C NMR (100 MHz, CDCl3):
149.3, 143.1, 140.8,
139.1, 138.5, 136.7, 136.0, 131.4, 129.1, 119.4, 118.6, 117.9; 19F
NMR (376 MHz, CDCl3):
7.07 (d, J = 8 Hz, 1H), 6.96–6.92 (m, 2H), 2.32 (s, 3H); 13C NMR
(100 MHz, CDCl3): 150.1, 143.4, 141.2, 139.2, 136.7, 136.0, 135.7,
127.6, 126.7, 116.2, 115.6, 19.4; 19F NMR (376 MHz, CDCl3):
d
d
d
d
À140.81 (dd, J1 = 22.6 Hz, J2 = 7.5 Hz, 1F),
À141.44 (dd, J1 = 18.8 Hz, J2 = 7.5 Hz 1F), À157.97 (m, 1F), À159.21
(m, 1F), À163.07 (m, 1F); MS (EI): 286; HRMS calcd for C13H6F4OS:
286.0075, found: 286.0073.
À157.01 (t, J = 18.8 Hz, 1F), À158.36 (dd, J1 = 18.8 Hz, J2 = 7.5 Hz,
1F), À162.00 (t, J = 22.6 Hz, 1F); MS (EI): 352; HRMS calcd for
C
12H3F4BrOS: 349.9024, found: 351.9005.
4.2.3. Compound 3c
4.2.10. Compound 3k
White solid; mp 85.8–88.4 8C; 1H NMR (400 MHz, CDCl3):
d
6.97
(d, J = 4 Hz, 2H), 6.92 (s, 1H), 2.28 (s, 3H); 13C NMR (100 MHz,
CDCl3): 148.2, 143.3, 141.0, 139.3, 138.5, 136.7, 136.1, 135.6,
129.2, 127.1, 117.8, 20.6; 19F NMR (376 MHz, CDCl3):
White solid; mp 78.8–81.7 8C; 1H NMR (400 MHz, CDCl3):
d 7.27
(d, J = 4.0 1H), 7.21 (dd, J1 = 8.0 Hz, J2 = 4.0 Hz, 1H), 6.98 (d,
J = 8.0 Hz 1H); 13C NMR (100 MHz, CDCl3):
150.7, 143.4, 141.2,
139.3, 138.7, 136.9, 136.2, 132.1, 128.7, 127.7, 121.5, 115.7; 19F
NMR (376 MHz, CDCl3):
1F), À158.22 (dd, J1 = 18.8 Hz, J2 = 7.5 Hz, 1F), À161.86 (t,
J = 22.6 Hz, 1F); MS (EI): 352; HRMS calcd for C12H3F4BrOS:
349.9024, found: 349.9023.
d
d
d
À141.37
(m, 1F), À158.13 (m, 1F), À159.08 (m, 1F), À163.15 (m, 1F); MS
d
À140.87 (m, 1F), À157.08 (t, J = 18.8 Hz,
(EI): 286; HRMS calcd for C13H6F4OS: 286.0075, found: 286.0072.
4.2.4. Compound 3d
White solid; mp 102.8–105.0 8C; 1H NMR (400 MHz, CDCl3):
d
7.01 (d, J = 8 Hz, 1H), 6.70 (dd, J1 = 8 Hz, J2 = 4 Hz, 1H), 6.64 (d,
J = 4 Hz, 1H), 3.76 (s, 3H); 13C NMR (100 MHz, CDCl3):
156.9,
144.0, 143.2, 141.0, 139.1, 138.4, 136.7, 135.8, 118.7,117.2, 113.9,
111.7, 55.8; 19F NMR (376 MHz, CDCl3):
J2 = 7.5 Hz, 1F), À157.87 (t, J = 15.0 Hz, 1F), À159.05 (m, 1F),
À163.10 (m, 1F); MS (EI): 302; HRMS calcd for C13H6F4O2S:
302.0025, found: 302.0022.
4.2.11. Compound 3l
d
White solid; mp 73.5–74.8 8C; 1H NMR (400 MHz, CDCl3):
d
7.13
(d, J = 4.0 Hz, 1H), 7.09–7.03 (m, 2H); 13C NMR (100 MHz, CDCl3):
150.7, 146.0, 143.4, 141.0, 139.3, 138.7, 136.3, 134.1, 127.5, 125.9,
118.7, 115.1; 19F NMR (376 MHz, CDCl3):
d
d
À141.24 (dd, J1 = 22.6 Hz,
d
À140.90 (m, 1F),
À157.14 (m, 1F), À158.26 (m, 1F), À161.89 (m, 1F); MS (EI): 306;
HRMS calcd for C12H3F4BrOS: 305.9529, found:305.9532.
4.2.5. Compound 3e
Acknowledgement
White solid; mp 83.0–84.8 8C; 1H NMR (400 MHz, CDCl3):
d
7.00 (d, J = 8 Hz, 1H), 6.69 (d, J = 4 Hz, 1H), 6.66 (dd, J1 = 8 Hz,
J2 = 4 Hz, 1H), 3.79 (s, 3H); 13C NMR (100 MHz, CDCl3):
160.4,
151.4, 143.0, 140.9, 139.4, 138.5, 136.5, 134.4, 127.2, 112.1, 104.3,
55.3; 19F NMR (376 MHz, CDCl3):
J2 = 7.5 Hz, 1F), À158.15 (t, J = 18.8 Hz, 1F), À158.95 (m, 1F),
À162.74 (m, 1F); MS (EI): 302; HRMS calcd for C13H6F4O2S:
302.0025, found: 302.0031.
This work was supported financially by National Natural
Science Foundation of China (21176222).
d
d
À141.20 (dd, J1 = 22.6 Hz,
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.jfluchem.2013.
05.023.
4.2.6. Compound 3f
White solid; mp 87.4–89.7 8C; 1H NMR (400 MHz, CDCl3):
d
7.03
(d, J = 8 Hz, 1H), 6.97–6.93 (m, 2H), 2.89–2.83 (m, 1H), 1.24 (s, 3H),
1.22 (s, 3H); 13C NMR (100 MHz, CDCl3):
150.2, 149.9,142.9,
140.5, 138.9, 138.1, 136.4, 135.6, 126.3, 123.6, 115.8, 112.6,33.5,
23.4; 19F NMR (376 MHz, CDCl3):
À141.33 (dd, J1 = 22.6 Hz,
J2 = 7.5 Hz, 1F), À158.20 (t, J = 18.8 Hz, 1F), À159.06 (dd,
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