Copper-catalysed direct difluoromethylselenolation of aryl boronic acids with Se-(difluoromethyl) 4-methylbenzenesulfonoselenoate

Article abstract of DOI:10.1016/j.tetlet.2021.152897

In this study, we developed the first copper-catalysed direct difluoromethylselenolation of aryl boronic acids using Se-(difluoromethyl) 4-methylbenzenesulfonoselenoate as a difluoromethylselenolation reagent. Owing to the cheap and readily accessible reagents, broad substrate scope, and mild reaction conditions, this is an alternative and practical strategy for the synthesis of aryl difluoromethylselenylether.

Full text of DOI:10.1016/j.tetlet.2021.152897

Tetrahedron Letters 68 (2021) 152897
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Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Copper-catalysed direct difluoromethylselenolation of aryl boronic acids
with Se-(difluoromethyl) 4-methylbenzenesulfonoselenoate
a
a
a
a
b,
Kui Lu a, , Xiaolan Xi , Ting Zhou , Lingyu Lei , Quan Li , Xia Zhao
⇑
⇑
a China International Science and Technology Cooperation Base of Food Nutrition/Safety and Medicinal Chemistry, College of Biotechnology, Tianjin University of Science &
Technology, Tianjin 300457, China
b College of Chemistry, Tianjin Key Laboratory of Structure and Performance for Functional Molecules, Tianjin Normal University, Tianjin 300387, China
a r t i c l e i n f o
a b s t r a c t
Article history:
In this study, we developed the first copper-catalysed direct difluoromethylselenolation of aryl
boronic acids using Se-(difluoromethyl) 4-methylbenzenesulfonoselenoate as a difluoromethylselenola-
tion reagent. Owing to the cheap and readily accessible reagents, broad substrate scope, and mild
reaction conditions, this is an alternative and practical strategy for the synthesis of aryl
difluoromethylselenylether.
Received 3 December 2020
Revised 25 January 2021
Accepted 28 January 2021
Available online 5 February 2021
Ó 2021 Published by Elsevier Ltd.
Keywords:
Copper-catalysed
Aryl boronic acid
Se-(difluoromethyl) 4-
methylbenzenesulfonoselenoate
Introduction
was first synthesised by our group as an SeCF2H source [11].
Besides arylamines, aryl boronic acids are readily accessible and
Organofluorine compounds are widely used in academia and
industry [1]. Incorporation of fluoroalkyl moieties into organic
molecules can alter their physicochemical properties and biologi-
cal activities significantly [2]. Over the past decade, a combination
of fluoroalkyl groups and chalcogens, such as OCF3 [3], OCF2H [4],
SCF3 [5], and SCF2H [6] has attracted significant research attention
due to their high lipophilicity and good cell membrane permeabil-
ity. Recently, great progress has been made on the introduction of
trifluoromethylselanyl group (SeCF3) into organic molecules [7].
However, the difluoromethylselenol group (HCF2Se) has not been
explored much [8], although it is a potential lipophilic isostere of
OH, SH, and NH. The lack of studies on this group can be attributed
to the easily oxidisable nature of selenium-containing molecules
and their high toxicity and unpleasant odour [9]. The lack of effi-
cient difluoromethylselenolation reagents could be another bottle-
neck in the synthesis of HCF2Se-containing compounds.
widely used in many organic transformations as the key starting
material. In 2017, Tlili and Billard reported a copper-catalyzed
direct trifluoro- and perfluoroalkylselenolations of boronic acids
with perfluoroalkyl tolueneselenosulfonates [12]. Inspired by this
work, we report the copper-catalysed direct difluoroselenolation
of aryl boronic acids with TsSeCF2H (Scheme 1).
Due to our interest in the direct incorporation of fluoroalkyl-
chalcogen groups into organic molecules [10], we previously devel-
oped the metal-free, photocatalysed difluoromethylselenolation of
arylamines under visible light using shelf-stable Se-(difluo-
romethyl) 4-methylbenzenesulfonoselenoate (TsSeCF2H), which
⇑
Corresponding authors.
E-mail addresses: lukui@tust.edu.cn (K. Lu), hxxyzhx@mail.tjnu.edu.cn (X. Zhao).
Scheme 1. Synthesis of aryl difluoromethylselenylether or aryl difluoromethylse-
lenylether with TsSeCF2H or TsSeRF.
https://doi.org/10.1016/j.tetlet.2021.152897
0040-4039/Ó 2021 Published by Elsevier Ltd.

K. Lu, X. Xi, T. Zhou et al.
Tetrahedron Letters 68 (2021) 152897
was found to give the best yield (Entries 23–26). Increasing the
reaction temperature to 40 °C decreased the yield to 78% (Entry
27). Decreasing the catalyst and ligand loadings to 0.05 equiv. or
increasing them to 0.15 equiv. also decreased the yield (Entries
28 and 29). When the concentration of 1a was increased to
0.3 M or decreased to 0.1 M, the yield decreased to 67% and 75%,
respectively (Entries 30 and 31). Increasing the loading of 2 to
1.2 equiv. increased the yield to 86% (Entry 32). Moreover, when
the concentration of 1a was increased to 1.2 equiv., the yield
increased to 90% (Entry 33). Thus, the optimal reaction conditions
for the difluoroselenolation of 1a were as follows: 1a: 0.36 mmol,
2: 0.30 mmol, Cu(OAc)2: 0.03 mmol, 4,40-dimethyl-2,20-bipyridine:
0.03 mmol, K2CO3: 0.30 mmol, and CH3CN: 1.5 mL, temperature:
25 °C. Compared with Tlili and Billard’s protocol about the cop-
per-catalyzed direct trifluoro- and perfluoroalkylselenolations of
Results and discussion
To begin the investigation, (4-methoxyphenyl)boronic acid (1a)
was treated with TsSeCF2H (2) and caesium carbonate in the pres-
ence of copper(II) acetate catalyst and 2,20-bipyridine (L1) in 1,4-
dioxane at 25 °C. Fortunately, desired difluoroselenolation product
3a was obtained in 62% yield (Table 1, entry 1). Various solvents
such as tetrahydrofuran (THF), diglyme, acetonitrile (MeCN) 1,2-
dichloroethane (DCE), and N,N-dimethylformamide (DMF) (Table 1,
entries 2–6) were screened to improve the yield of this reaction,
and the best yield was obtained using MeCN. Following this, vari-
ous other catalysts such as copper(II) triflate, copper(II) bromide,
copper(II) trifluoroacetate, copper(I) iodide, copper(I) iodide,
cyanocopper, copper(I) triflate, copper(II) bromide, tetrakis(ace-
tonitrile)copper(I) tetrafluoroborate, and silver triflate and bases
including sodium carbonate, potassium carbonate, potassium
phosphate, potassium fluoride, potassium bicarbonate, triethy-
lamine, triethylenediamine (DABCO), and 1,8-diazabicyclo[5.4.0]
undec-7-ene (DBU) (Entries 7–22) were examined. Both copper(I)
and copper(II) catalysts with organic and inorganic bases were
compatible in this reaction. The combination of copper (II) acetate
with potassium carbonate resulted in the best yield. Ligand, cata-
lyst loading, and the effects of reaction temperature and concentra-
tion of the starting material were also investigated. Ligands such as
4,40-dimethyl-2,20-bipyridine (L2), 1,10-phenanthroline (L3), N1,
N1,N2,N2-tetramethylethane-1,2-diamine (L4), and 1,3-diphenyl-
propane-1,3-dione (L5) were examined for this reaction, and L2
boronic acids with perfluoroalkyl tolueneselenosulfonates,
slightly weaker base K2CO3 was used.
a
With the optimsed reaction conditions in hand, the generality of
this reaction was examined using a series of aryl boronic acids
(2b–2z). The substrate scope is summarised in Scheme 2.
2-Methoxyl, 3-methoxyl, di-methoxyl, and tri-methoxyl substi-
tuted phenylboronic acids (1b–1f) could be transformed to the cor-
responding difluoroselenolation products (3b–3f) in good yields.
Moreover, phenylboronic acids bearing electron donating or
electron withdrawing substituents in the para-, meta- or ortho-
positions were well-tolerated in this reaction, giving the desired
products (3g–3q) in moderate to excellent yields. To further
Table 1
Optimisation of difluoroselenolation of (4-methoxyphenyl)boronic.a
Entry
Catalyst/eq.
Ligand/eq.
Base
Solvent
Temperature (°C)
Yield (%)b
1
2
3
4
5
6
7
8
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OTf)2/0.1
CuBr2/0.1
Cu(CF3COO)2/0/1
CuI/0.1
CuCN/0.1
CuOTf/0.1
Cu(CH3CN)4BF4/0.1
AgOAc/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OTf)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OTf)2/0.05
Cu(OAc)2/0.15
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
Cu(OAc)2/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L1/0.1
L2/0.1
L3/0.1
L4/0.1
L5/0.1
L2/0.1
L2/0.05
L2/0.15
L2/0.1
L2/0.1
L2/0.1
L2/0.1
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Cs2CO3
Na2CO3
K2CO3
K3PO4
KF
1,4-dioxane
THF
Diglyme
MeCN
DCE
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
25
40
25
25
25
25
25
25
62
64
20
67
63
28
49
62
60
62
50
32
47
15
66
73
57
22
trace
62
62
trace
80
53
0
DMF
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
MeCN
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
KHCO3
Et3N
DABCO
DBU
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
K2CO3
32
78
73
77
67c
75d
86e
90f
a
1a (0.30 mmol), 2 (0.30 mmol), catalyst (0.015–0.045 mmol), ligand (0.015–0.045 mmol) and base (0.30 mmol) in solvent (1.5 mL) for indicated reaction temperature. b
c
d
e
f
Isolated yields. CH3CN (1.0 mL) was used. CH3CN (3.0 mL) was used. 2 (0.36 mmol) was used. 1a (0.36 mmol) was used.
2

K. Lu, X. Xi, T. Zhou et al.
Tetrahedron Letters 68 (2021) 152897
Scheme 4. Possible reaction mechanism.
Scheme 5. Scale up of the difluoromethylselenolation reaction.
molecular ion peak corresponding to 1,2-bis(difluoromethyl)dise-
lane could be identified from the reaction mixture by GC-MS.
Moreover, in the absence of boronic acid and base, only the peak
corresponding to the unknown species was detected after 12 h
under the optimised reaction conditions. When 1a and K2CO3 were
added to the above mixture, compound 3a was obtained after 12 h.
Treatment of compound 2 with K2CO3 or KOAc in MeCN resulted in
its degradation to the unknown species. When 2 was dissolved in
MeCN and stirred for 12 h at room temperature, the fluorine peak
of unknown species was not detected (Scheme 3) (See supporting
information for detail.). These observations suggested that the
unknown species was 1,2-bis(difluoromethyl)diselane, and it could
be a key intermediate in this transformation. However, we cannot
Scheme 2. Scope of difluoroselenolation of aryl boronic acids.
investigate the substrate scope of this reaction, a range of other
aryl boronic acids (1r–1z) were examined. To our delight, these
substrates were smoothly converted to the desired products
(3r–3z) in moderate to good yields.
eliminate the possibility of
reagent.
2 being the difluoroselenolation
To investigate the reaction mechanism, the difluoroselenolation
of 1a by 2 under the optimised reaction conditions was closely
monitored by 19F NMR using (trifluoromethyl)benzene as the
internal standard (d = ꢀ 63.20 ppm). After 15 min of initiation of
the reaction, three fluorine peaks were observed, which could be
assigned to 2 (d = ꢀ 91.06 ppm), product 3a (d = -90.47 ppm),
and an unknown species (d = ꢀ 88.59 ppm). After 30 min, the flu-
orine peak of compound 2 disappeared, and the fluorine peak
intensities of 3a and the unknown species increased. After 1 h,
the fluorine peak intensity of compound 3a increased continu-
ously, while that of the unknown species decreased. Notably, a
Based on literature [12] and the abovementioned results, a
plausible reaction mechanism for this transformation was pro-
posed (Scheme 4). First, 16-electron copper complex A was formed
in situ, which was the active catalytic species. This was followed by
transmetallation between complex A and the aryl boronic acid to
form intermediate B. Finally, B reacted with trifluoromethylseleno-
lated reagent 2 or 1,2-bis(difluoromethyl)diselane to give desired
product 3.
Finally, to illustrate the possible practical applications of this
transformation, a gram-scale difluoromethylselenolation reaction
of 1a was conducted (Scheme 5). To our delight, the desired pro-
duct 3a was obtained in 73% yield.
Conclusion
In summary, we developed the first copper-catalysed direct
difluoromethylselenolation of aryl boronic acids using TsSeCF2H
as a difluoromethylselenolation reagent. The cheap and readily
accessible reagents, broad substrate scope, and mild reaction con-
ditions render this reaction an alternative and practical strategy for
the synthesis of aryl difluoromethylselenylether. Investigation of
other difluoromethylselenolation reactions using TsSeCF2H are
underway in our lab.
Scheme 3. Additional reactions for investigating the mechanism.
3

K. Lu, X. Xi, T. Zhou et al.
Tetrahedron Letters 68 (2021) 152897
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Declaration of Competing Interest
The authors declare that they have no known competing finan-
cial interests or personal relationships that could have appeared
to influence the work reported in this paper.
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Acknowledgments
The authors sincerely thank the financial support from Natural
Science Foundation of Tianjin City (Grants 18JCQNJC76600) and
National Natural Science Foundation of China (Grants 21572158).
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Appendix A. Supplementary data
Supplementary data to this article can be found online at
https://doi.org/10.1016/j.tetlet.2021.152897.
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