Halogen exchange via a halogenation of diaryliodonium salts with cuprous halide

Article abstract of DOI:10.2174/15701786113109990011

An efficient halogenation reaction has been developed with diaryliodonium salts and cuprous halides. Various diaryliodonium salts 1 could perform the reaction with readily available CuBr or CuCl in CH₃CN at 80°C, assembling bromoarenes or chloroarenes in up to 92% yields. This provides us a method for the transformation from iodoarenes to other haloarenes.

Full text of DOI:10.2174/15701786113109990011

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Letters in Organic Chemistry, 2013, 10, 541-548
541
Halogen Exchange via a Halogenation of Diaryliodonium Salts with
Cuprous Halide
Jian Lia*, Li Liu b, Dong Dinga and Jiang-tao Suna
aSchool of Pharmaceutical Engineering & Life Sciences, Chang Zhou University, Changzhou, 213164, P.R. China
bAnalytical Center, Chang Zhou University, Changzhou, 213164, P.R. China
Received February 18, 2013: Revised June 08, 2013: Accepted June 10, 2013
Abstract: An efficient halogenation reaction has been developed with diaryliodonium salts and cuprous halides. Various
diaryliodonium salts 1 could perform the reaction with readily available CuBr or CuCl in CH3CN at 80°C, assembling
bromoarenes or chloroarenes in up to 92% yields. This provides us a method for the transformation from iodoarenes to
other haloarenes.
Keywords: Diaryliodonium salts, Halogenation, Cuprous halide, Aromatic halides, Iodoarenes.
INTRODUCTION
extent, the synthetic pathway of aromatic halides is the
halogenations of an arylmetallic species.
Hypervalent iodine compounds are of great interest as
mild, nontoxic, and selective reagents in organic synthesis
[1]. Diaryliodonium salts are the best known compounds in
this class. Several studies in the literature have reported the
application of diaryliodonium salts because of their highly
electron-deficient nature and excellent leaving-groupability,
usually they serve as versatile arylating agents with variety
of nucleophiles, such as indoles, pyrroles, phenols,
carboxylic acids, aniline and carbonyls [2]. In particular, the
groups of Gaunt and Olofsson have conducted lots of work
with the synthesis and applications of diaryliodonium salts.
Recently, they developed efficient one-pot routes to
diaryliodonium salts, and these compounds are now
inexpensive and easily available [3].
Recent year, Carroll and Widdowson reported the
fluorination of diaryliodonium salts with CsF and many
fluorine-18 labeled arenes and heterocycles were synthesized
through this way (Scheme 1) [9]. This provides us with a
simple method for the synthesis of fluoro aromatics. As part
of our ongoing interest in developing application of
diaryliodonium salts [10], we herein wish to report a simple,
efficient method for preparation of aromatic halides with
copper halide (Scheme 1). This provides us a method for the
halogen exchange of aryl halides.
RESULTS AND DISCUSSION
Our initial study was focused on the reaction of
diphenyliodonium salt 1a and several halogen sources, but
KBr or KCl gave the negative results, therefore no product
was detected (entry 1, 2, Table 1). It was pleased that 25%
yield of bromobenzene 2a was collected by employing CuBr
in DMF at room temperature for 24 hours (entry 3, Table 1).
So we carried on our investigations using diphenyliodonium
salt 1a and CuBr as model substrates, after testing various
reaction conditions for the bromination of diphenyliodonium
salt 1a, the results was summed up in (Table 1). The reaction
proceeds in various solvents, such as DMSO, DMAC, THF,
CH3CN, DCM and H2O. CH3CN was found to be the solvent
of choice regarding both the yield and the reaction rate to
give product bromobenzene in 45% yield (entry 7). When 2
equiv of K2CO3 was used, 38% yield was obtained (entry
10). Gratifyingly, when the temperature was increased from
25°C to 80°C, the yield was promoted to 91% after 2 hours.
Encouraged by these results, CuBr2 was employed for this
bromination under the same condition, but desired result was
not obtained, the yield was decreased to 73% (entry 12).
For many decades, aromatic halides have been an
important class of compounds, due to their role as precursors
for the synthesis of organo metallic reagents [4] and for
nucleophilic substitution reactions [5] In addition, with the
advent of cross-coupling chemistry [6], the importance of
bromo- and chloro- arenes has tremendously increased, and
hence they can be classified as the core building blocks of
organic synthesis. Consequently, efficient and selective
methods to access this class of compounds are highly
valuable. As a result, considerable efforts have been directed
toward the development of efficient and selective methods
for preparation of aromatic halides.
The traditional synthetic method of aromatic
halogenations includes electrophilic aromatic substitution,
conversion of an amine to a halide via the diazonium salt
(the Sandmeyer reaction) [7]. For example, aryl bromides are
synthesized from arenediazonium salt and HBr, the reaction
requires an excess of CuBr and concentrated acid at high
temperatures (up to 100-120°C) [8]. In addition, to a lesser
In addition, studies about the influence of different
diphenyliodonium anions were carried out, satisfactory
results could be obtained with diaryliodonium 4-methy-lben-
zenesulfonate, chloride, bromide, tetrafluoroborates, hexa-
*Address correspondence to this author at the School of Pharmaceutical
Engineering & Life Sciences, Chang Zhou University, Changzhou, 213164,
P.R. China; Fax: (+86)-519-8633-4597; E-mail: lijianchem@gmail.com
1875-6255/13 $58.00+.00
© 2013 Bentham Science Publishers

542 Letters in Organic Chemistry, 2013, Vol. 10, No. 8
Li et al.
R2
F
Literature 9
This study
CsF or KF
R1
R1
R2
X
R2
R2
HX
I
I
Cl
CuCl
(1.5 equiv.)
(1.5 equiv.)
R1
R1
mCPBA,
R2
R2
Br
CuBr
This study
R1
Scheme 1. Halogen exchange from Iodine to the other halogens.
Table 1. Optimization of the Model Reaction a
X
I
Br
or
Cl
Copper Halide
+
Solvent
1a
2
Entry
Halide Resources
X
Solvent
T(ꢀ)
Yield(%) b
1
2
KBr
KCl
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTf
OTs
Br
CH3CN
CH3CN
DMF
25
25
25
25
25
25
25
25
25
25
80
80
80
80
80
80
80
80
80
-
-
3
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr
CuBr2
CuBr
CuBr
CuBr
CuBr
CuBr
CuCl
CuCl2
25
13
21
5
4
DMSO
DMAC
THF
5
6
7
CH3CN
CH2Cl2
H2O
45
23
11
38
91
73
71
40
45
63
65
88
65
8
9
10 c
11
12
13
14
15
16
17
18
19
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
CH3CN
Cl
BF4
PF6
OTf
OTf
a Diphenyliodonium salt (0.5 mmol) and copper halide (0.75 equiv) were mixed in solvent (1 mL) at r. t. , then heating to 80 ºC for 2 hours.
b Isolated yield.
c K2CO3 (1mmol) was added.
fluorophosphates under(entries 12-17, Table 1). It’s noted
that the effect of different anions on the reactivity of
diphenyliodonium salts were different, which was due to the
different solubilities and nucleophilicities of diaryliodonium
salts 1c. Moreover, the search for chlorination of
diphenyliodonium salt 1a was investigated, CuCl was chosen
correspondingly as chlorination reagents, 88% of yield was
obtained in CH3CN at 80 °C in 2 hours (entry 18, Table 1).

Halogen Exchange via a Halogenation of Diaryliodonium Salts with Cuprous Halide
Letters in Organic Chemistry, 2013, Vol. 10, No. 8 543
Table 2. Bromination of Diaryliodonium Salts with CuBr a
OTf
I
Br
CH3CN, 80 oC
CuBr
+
R
R
2
1
Entry
Substrate
Product
Br
Yield (%) b
OTf
I
1
91
2a
1a
OTf
I
Br
2
85
Cl
MeOOC
NC
Cl
2b
1b
OTf
Br
I
3
4
83
89
MeOOC
2c
1c
OTf
Br
I
NC
2d
1d
Br
OTf
I
5
6
87
92
2e
1e
OTf
Cl
Br
Cl
I
2f
1f
F
Br
OTf
F
I
7
8
91
64
2g
1g
OTf
MeO
Br
MeO
I
2h
1h

544 Letters in Organic Chemistry, 2013, Vol. 10, No. 8
Li et al.
Table 2. Contd….
Entry
Substrate
Product
Br
Yield (%) b
F
OTf
I
9
71
F
2i
1i
OMe
OTf
Br
I
10
47
OMe
2j
1j
a Diaryliodonium salt (0.5 mmol) and CuBr (0.75 mmol) were mixed in CH3CN (1 mL) at r. t., then heating to 80 ºC for 2 hours.
b Isolated yield.
OTf
I
CuBr or CuCl (1.5equiv.)
or
Br
CH3CN, 80 oC
S
S
Cl
S
2t
2u
trace
1r
trace
Scheme 2. Halogenation of Diaryliodonium Salts 1r.
With optimized reaction conditions in hand, we probed
the scope of diaryliodonium salts with CuBr in CH3CN at 80
ºC. The results are summarized in (Table 2). The reaction
scope was subsequently explored by using a series of
asymmetrical diaryliodonium salts 1, which were prepared
from appropriate iodoarene under simple procedure [10, 11].
Common functional groups, such as fluorine, chlorine, ester,
cyano, phenyl and methoxy groups were well tolerated under
the standard reaction conditions (entries 2-9, Table 2). The
diaryliodonium salts bearing an electron-withdrawing group
on benzene ring resulted in better yield (entries 3, 4, Table 2)
than the one bearing an electron-donating group (entry 8,
Table 2).
optimized reaction conditions (entries 8, 9). Functional
group in the meta- position was very well tolerated, as
demonstrated by chlorination with salt 1q to yield product 2s
(entry 10).
The present reaction was also examined with heterocyclic
diaryliodonium salts, such as thiophene (Scheme 2). But
only products 2t and 2u were detected by GC-MS .
The plausible mechanism of this halogenation reaction is
depicted in (Fig. 1). At first, oxidative addition of CuX with
diaryliodonium salts occurred in the reaction system, which
afforded copper-complex
3
by eliminating of 2-
iodomesitylene. Elimination of (Trifluoromethylsulfonyloxy)
copper from intermediate 3 afforded product 2.
It is interesting that substituent groups in the meta-
position were very well tolerated and gave corresponding
products 2f-g in higher yields (entries 6, 7, Table 2).
Likewise, ortho-substituted salts posed no problem in this
reaction, as exemplified by o-methyl product (entry 10).
CONCLUSION
In conclusion, an efficient halogenation reaction has been
developed with diaryliodonium salts and cuprous halide.
Various diaryliodonium salts 1 could perform the reaction
with readily available CuBr or CuCl in CH3CN at 80°C,
assembling bromoarenes or chloroarenes in up to 92%
yields. This provides a method for the transformation
iodoarenes to other haloarenes. Further investigations on
reaction mechanism and other synthetic utility of
diaryliodonium salts are currently underway.
The results encouraged us to extend our protocol to
investigate this halogenation method. In this regard
chlorination of diaryliodonium salts 1 with CuCl was
surveyed under the optimized reaction conditions. To our
delight, the results exceeded our expectations; we found that
this methodology was broadly applicable to a variety of
asymmetrical diaryliodonium salts 1, affording halogenation
products in synthetically valuable yields (Table 3).
Substituted
diphenyliodoniumtriflate
with
electron-
EXPERIMENTAL
withdrawing substituents worked equally well as those with
electron-donating substituents, giving chlorobenzenes 2l-p in
high yields (entries 2-7, Table 3). In particular,
diaryliodonium salts of 4-tert-butylbenzene 1n resulted in
higher yield of product 2o (entry 6). These ortho-substituted
products 2q and 2r were obtained in good yields under
General Procedure for Halogenation Reaction of
Diaryliodonium Salts with Cuprous Halide
A mixture of diaryliodonium salt (0.5 mmol), cuprous
halide (0.75 mmol) and CH3CN (1mL) was taken in a 10mL

Halogen Exchange via a Halogenation of Diaryliodonium Salts with Cuprous Halide
Letters in Organic Chemistry, 2013, Vol. 10, No. 8 545
Table 3. Chlorination of Diaryliodonium Salts with CuCl a
OTf
I
Cl
CH3CN, 80 oC
+
R
CuCl
R
2
1
Entry
Substrate
Product
Yield (%) b
Cl
OTf
I
1
88
2k
1a
OTf
I
Cl
2
85
F
F
2l
1k
OTf
I
Cl
Cl
3
4
5
83
89
87
Cl
Br
Cl
Br
2m
1b
OTf
I
2b
2n
1l
OTf
Cl
I
I
MeO
MeO
1m
1n
OTf
Cl
6
92
2o
OTf
Cl
I
7
8
91
64
NC
NC
2p
2q
1d
Cl
OTf
Cl
Cl
I
1o

546 Letters in Organic Chemistry, 2013, Vol. 10, No. 8
Li et al.
Table 3. Contd......
Entry
Substrate
Product
Yield (%) b
Br
OTf
Cl
I
9
80
Br
2r
1p
OTf
O2N
Cl
O2N
I
10
85
2s
1q
a Diaryliodonium salt (0.5 mmol) and CuCl (0.75 mmol) were mixed in CH3CN (1 mL) at r. t., then heating to 80 ºC for 2 hours.
b Isolated yield.
I
OTf
OTf
I
Cu
III
X
X
CuOTf
R
CuX
+
R
R
1
3
2
Fig. (1). Possible mechanism of the halogenations.
reaction tube and heated at 80°C temperature for 2 hours
under vigorous stirring. After completion of the reaction
(observed on TLC or GC) the reaction mass was cooled to
room temperature, and 5 ml of water was added. The mixture
was stirred for 10 mins, the product was extracted with ethyl
acetate (3 * 10mL). The organic layer was washed with
water and dried over anhydrous sodium sulphate. Solvent
was evaporated under reduced pressure to obtain the product.
The crude product was purified on silica gel column by using
petroleum ether and ethyl acetate as solvents to obtain the
pure product. The obtained product was analyzed by 1H
NMR, 13C NMR.
4-Bromobenzonitrile (2d) [15]
1
Yield: 81mg (89%) H NMR (400 MHz, CDCl3): ꢀ =
7.64 (d, J = 7.6 Hz, 2H), 7.51 (d, J = 8.4 Hz, 2H). 13C NMR
(125 MHz, CDCl3): ꢀ = 134.01, 132.62, 128.01, 118.05,
111.23.
4-Bromobiphenyl (2e) [14]
1
Yield: 101mg (87%) H NMR (400 MHz, CDCl3): ꢀ =
7.54 (m, 4H), 7.43 (m, 4H), 7.35 (m, 1H). 13C NMR (125
MHz, CDCl3): ꢀ = 140.15, 140.01, 131.86, 128.93, 128.90,
128.87, 128.78, 128.75, 127.64, 126.95, 121.54;
Bromobenzene (2a) [12]
1-Bromo-3-chlorobenzene (2f) [12]
1
Yield: 71mg (91%) H NMR (400 MHz, CDCl3): ꢀ =
1
Yield: 87mg (92%) H NMR (400 MHz, CDCl3): ꢀ =
7.50 (d, J = 7.2 Hz, 2H), 7.29 (m, 3H). 13C NMR (125 MHz,
CDCl3): ꢀ = 131.57, 131.54, 131.51, 130.07, 130.04, 130.01,
126.88, 122.52.
7.52 (d, J = 0.8 Hz, 1H), 7.37 (d, J = 8.4 Hz, 1H), 7.21 (m,
1H), 7.16 (m, 1H). 13C NMR (125 MHz, CDCl3): ꢀ = 135.18,
131.50, 130.78, 129.79, 127.35, 122.80.
1-Bromo-4-chlorobenzene (2b) [13]
1-Bromo-3-fluorobenzene (2g) [16]
1
Yield: 81mg (85%) H NMR (400 MHz, CDCl3): ꢀ =
1
7.42 (d, J = 8.4 Hz, 2H), 7.21 (d, J = 8.0 Hz, 2H). 13C NMR
(125 MHz, CDCl3): ꢀ = 133.22, 132.82, 132.80, 132.77,
132.74, 130.23, 130.20, 130.17, 120.27.
Yield: 79mg (91%) H NMR (400 MHz, CDCl3): ꢀ =
7.27 (m, 3H), 7.00 (m, 1H). 13C NMR (125 MHz, CDCl3): ꢀ
= 163.70, 161.70, 131.01, 130.94, 127.50, 127.49, 127.47,
127.44, 127.42, 127.38, 127.37, 122.65, 122.57, 119.32,
119.29, 119.12, 114.34, 114.18.
Methyl 4-bromobenzoate (2c) [14]
1
Yield: 89mg (83%) H NMR (400 MHz, CDCl3): ꢀ =
1-Bromo-3-methoxybenzene (2h) [12]
7.88 (d, J = 8.4 Hz, 2H), 7.56 (d, J = 8.0 Hz, 2H), 3.91(s,
3H). 13C NMR (125 MHz, CDCl3): ꢀ = 166.37, 131.72,
131.12, 129.06, 128.05, 52.30.
1
Yield: 60mg (64%) H NMR (400 MHz, CDCl3): ꢀ =
7.13 (m, 3H), 6.83 (d, J = 8.0 Hz, 1H), 3.78(s, 3H). 13C NMR

Halogen Exchange via a Halogenation of Diaryliodonium Salts with Cuprous Halide
Letters in Organic Chemistry, 2013, Vol. 10, No. 8 547
(125 MHz, CDCl3): ꢀ = 160.37, 130.52, 123.76, 122.82,
117.16, 113.10, 113.07, 55.42.
1-Bromo-2-chlorobenzene (2r) [20]
1
Yield: 76mg (80%) H NMR (400 MHz, CDCl3): ꢀ =
7.62 (d, J = 8.0 Hz, 1H), 7.45 (d, J = 8.0 Hz, 1H), 7.24 (m,
1H), 7.11 (m, 1H). 13C NMR (125 MHz, CDCl3): ꢀ = 134.55,
133.85, 130.49, 128.47, 127.93, 122.58.
1-Bromo-2-fluorobenzene (2i) [17]
1
Yield: 62mg (71%) H NMR (400 MHz, CDCl3): ꢀ =
7.54 (m, 1H), 7.28 (m, 1H), 7.13 (m, 1H), 7.04 (m, 1H). 13C
NMR (125 MHz, CDCl3): ꢀ = 160.11, 158.15, 133.61,
128.98, 128.92, 125.29, 125.26, 116.64, 116.46, 109.15,
108.98.
1-Chloro-3-nitrobenzene (2s) [13]
1
Yield: 67mg (85%) H NMR (400 MHz, CDCl3): ꢀ =
8.22 (s, 1H), 8.14 (d, J = 8.4 Hz, 1H), 7.69 (d, J = 8.0 Hz,
1H), 7.76 (t, J = 8.0 Hz, 1H). 13C NMR (125 MHz, CDCl3): ꢀ
= 148.81, 135.44, 134.72, 134.69, 130.40, 123.91, 121.76,
121.71, 121.66.
1-bromo-2-methoxybenzene (2j) [18]
1
Yield: 43mg (47%) H NMR (400 MHz, CDCl3): ꢀ =
7.76 (m, 1H), 7.33 (m, 1H), 6.84 (m, 1H), 6.73 (m, 1H), 3.88
(s, 3H). 13C NMR (125 MHz, CDCl3): ꢀ = 158.06, 139.49,
129.52, 122.50, 110.99, 85.97, 56.27.
CONFLICT OF INTEREST
The authors confirm that this article content has no con-
flict of interest.
Chlorobenzene (2k) [12]
1
Yield: 48mg (88%) H NMR (300 MHz, CDCl3): ꢀ =
7.35 (m, 3H), 7.32 (m, 1H), 7.25 m, 1H). 13C NMR (75
MHz, CDCl3): ꢀ = 134.25 129.73, 128.62, 126.45.
ACKNOWLEDGEMENTS
We are grateful to the grants from the Foundation of
Chang Zhou Municipal Bureau of Science and Technology
(No. KYZ1102100C) and the Priority Academic Program
Development of Jiangsu Higher Education Institutions.
1-Chloro-4-fluorobenzene (2l) [12]
1
Yield: 55mg (85%) H NMR (400 MHz, CDCl3): ꢀ =
7.28 (m, 2H), 6.99 (m, 2H). 13C NMR (125 MHz, CDCl3): ꢀ
= 162.31, 160.35, 129.99, 129.97, 129.95, 129.92, 129.18,
129.16, 116.83, 116.79, 116.64.
SUPPLEMENTARY MATERIAL
1,4-Dichlorobenzene (2m) [13]
Supplementary material is available on the publishers
Web site along with the published article.
1
Yield: 61mg (83%) H NMR (400 MHz, CDCl3): ꢀ =
7.43 (m, 2H), 7.24 (m, 2H). 13C NMR (125 MHz, CDCl3): ꢀ
= 135.03, 130.47, 128.75, 126.93, 126.90.
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1-Chloro-4-methoxybenzene (2n) [13]
1
Yield: 62mg (87%) H NMR (400 MHz, CDCl3): ꢀ =
7.28 (m, 2H), 6.99 (m, 2H), 3.35 (s, 3H). 13C NMR (125
MHz, CDCl3): ꢀ = 158.20, 129.30, 125.53, 115.21, 115.18,
55.49.
[2]
1-tert-Butyl-4-chlorobenzene (2o) [13]
1
Yield: 77mg (92%) H NMR (400 MHz, CDCl3): ꢀ =
7.38 (d, J = 8.4 Hz, 2H), 7.25 (d, J = 8.0 Hz, 2H), 1.29 (s,
9H). 13C NMR (125 MHz, CDCl3): ꢀ = 150.12, 131.09,
131.08, 131.06, 131.00, 130.99, 130.97, 130.96, 130.94,
127.25, 127.24, 127.22, 127.19, 127.16, 127.14, 119.21,
34.52, 31.33, 31.32, 31.30, 31.29, 31.27, 31.26, 31.24, 31.21,
31.15.
[3]
[4]
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and Heterocyclic Systems. Curr. Org. Chem. 2003, 7, 275-300. (b)
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Grignard Reagents, New York, 1996.
4-Chlorobenzonitrile (2p) [15]
1
Yield: 62mg (91%) H NMR (400 MHz, CDCl3): ꢀ =
7.61 (d, J = 7.6 Hz, 2H), 7.47 (d, J = 8.0 Hz, 2H). 13C NMR
(125 MHz, CDCl3): ꢀ = 139.58, 133.40, 129.72, 117.97,
110.82.
1,2-Dichlorobenzene (2q) [19]
[5]
[6]
Knipe, A. J., Eds.; Crampton, M. R. in Organic Reaction
Mechanism; Wiley: New York, 2007.
1
Yield: 47mg (64%) H NMR (400 MHz, CDCl3): ꢀ =
Diederich, F.; Stang, P. J., Eds.; Metal Catalyzed Cross Coupling
Reactions; Wiley-VCH: Weinheim, 1998.
7.43 (m, 2H), 7.25 (m, 2H). 13C NMR (125 MHz, CDCl3): ꢀ
= 132.57, 130.54, 127.75, 127.71, 127.68.

548 Letters in Organic Chemistry, 2013, Vol. 10, No. 8
Li et al.
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