Rapid microwave-promoted base-free Suzuki coupling reaction of sodium tetraphenylborate with hypervalent iodonium compounds in water

Article abstract of DOI:10.1080/00397910600588454

The palladium chloride-catalyzed Suzuki coupling reaction of sodium tetraphenylborate with hypervalent iodonium salts and iodanes was achieved under microwave irradiation in water without base. A convenient and rapid method for formation of carbon-carbon bonds had excellent yields. Copyright Taylor & Francis Group, LLC.

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Rapid Microwave‐Promoted Base‐Free
Suzuki Coupling Reaction of Sodium
Tetraphenylborate with Hypervalent
Iodonium Compounds in Water
Jie Yan a , Zhongshi Zhou b & Min Zhu b
a College of Chemical Engineering and Materials Sciences, Zhejiang
University of Technology, Hangzhou, Zhejiang, China
b College of Biological and Environmental Sciences, Zhejiang Shuren
University, Hangzhou, Zhejiang, China
Published online: 21 Aug 2006.
To cite this article: Jie Yan , Zhongshi Zhou & Min Zhu (2006): Rapid Microwave‐Promoted Base‐Free Suzuki
Coupling Reaction of Sodium Tetraphenylborate with Hypervalent Iodonium Compounds in Water, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry, 36:11,
1495-1502
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Synthetic Communicationsw, 36: 1495–1502, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600588454
Rapid Microwave-Promoted Base-Free
Suzuki Coupling Reaction of Sodium
Tetraphenylborate with Hypervalent
Iodonium Compounds in Water
Jie Yan
College of Chemical Engineering and Materials Sciences,
Zhejiang University of Technology, Hangzhou, Zhejiang, China
Zhongshi Zhou and Min Zhu
College of Biological and Environmental Sciences, Zhejiang Shuren
University, Hangzhou, Zhejiang, China
Abstract: The palladium chloride–catalyzed Suzuki coupling reaction of sodium tetra-
phenylborate with hypervalent iodonium salts and iodanes was achieved under
microwave irradiation in water without base. A convenient and rapid method for
formation of carbon–carbon bonds had excellent yields.
Keywords: Iodane, iodonium salt, microwave irradiation, sodium tetraphenylborate,
Suzuki reaction
The Suzuki reaction is one of the most versatile and utilized reactions for the
selective construction of carbon–carbon bonds, in particular for the formation
of biaryls.[1] In the reaction, organoboranes are generally used to react with aryl
halides or triflates in organic solvents in the presence of base, and sometimes
it requires a longer reaction time and a higher reaction temperature.[2]
To improve and simplify the reaction protocol, hypervalent iodine
Received in Japan September 13, 2005
Address correspondence to Jie Yan, College of Chemical Engineering and Materials
Sciences, Zhejiang University of Technology, Hangzhou, 310032, Zhejiang, China.
Fax: þ86 (571) 88320238. E-mail: jieyan87@hotmail.com
1495

1496
J. Yan, Z. Zhou, and M. Zhu
compounds have been focused on as alternatives to replace aryl halides or
triflates because the high reactivity of hypervalent iodine compounds,
especially iodonium salts[3] in the reactions with nucleophiles. It is generally
explained by the “hyperleaving group” properties of the phenyliodanyl
group, which is a remarkably good nucleofuge with a leaving group ability
about 106 times greater than the triflate.[3h] A number of publications about
using iodonium salts in the Suzuki reaction have been reported in recent
years,[4] and one very interesting paper from Bumagin et al. was about a
mild Suzuki reaction in water medium.[4c] Because the Suzuki reaction is
usually carried out in organic solvents, Suzuki reactions only in neat water
using iodonium salts are few. However, in the report only three iodonium
salts were investigated to react with sodium tetraphenylborate. Therefore,
the development of a simple, wide, relatively mild, and environmentally
more benign Suzuki reaction is still a much-sought process.
Microwave-assisted organic syntheses have received great attention
because of their fast reaction rates, high purity of products, and ease of
manipulation.[5] In particular, the microwave-irradiated procedures in water
medium or in absence of solvents for organic synthesis have attracted con-
siderable interest in recent years due to their efficient and environmentally
benign conditions.[4,6]
Our recent interest has been in the development of new synthetic methods
using hypervalent iodine compounds as alternatives in place of aryl halides or
triflates. As part of a program to investigate the range of Suzuki reaction in
water medium, we have checked the reaction of sodium tetraphenylborate
with iodonium salts and iodanes under microwave irradiation. Now we
report here a rapid and efficient microwave-assisted Suzuki coupling
reaction using iodonium salts and iodanes in water without base.
At the beginning, we mixed equal equivalents of sodium tetraphenyl-
borate and diphenyliodonium chloride, two equivalents of sodium
carbonate, as well as a small amount (0.2 mol%) of palladium chloride as
catalyst in water; we found that after only 20 s a near quantitative biphenyl
was afforded under a microwave-assisted condition. Then, we repeated the
same reaction without base; the reaction was also found to occur easily and
gave the same yield product. The result prompted us to further investigate
the reactions of sodium tetraphenylborate (1) with a series of iodonium salts
(2) under the same reaction conditions. They are shown in Scheme 1, and
the results are summarized in Table 1.
From Table 1, it is notable that except iodonium salt 2d (entry 4),
all iodonium salts reacted with sodium tetraphenylborate easily under
Scheme 1.

Rapid Microwave-Promoted Suzuki Reaction
1497
Table 1. Results of the coupling reaction of sodium tetraphenylborate with iodonium
salts under microwave irradiation
Entry
Iodonium salt
Ph2IþCl2
2a
(p-Me-C6H4)2 IþBr2
2b
(p-Br-C6H4)2 IþBr2
2c
(m-O2N- C6H4)2IþBr2
2d
Product
Ph-Ph
3a
Yielda (%)
1
2
3
4
5
98
99
97
85
93
p-Me-C6H4-Ph
3b
p-Br-C6H4-Ph
3c
m-O2N- C6H4-Ph
3d
p-MeO-C6H4-Iþ-PhBr2
2e
p-MeO-C6H4-Ph
3e
6
97
2f
3f
7
8
92
94
2g
3g
3h
2h
aIsolated yield.
microwave irradiation in 20 s and gave products in excess of 90% yield; some
of them were in almost quantitative yield. When asymmetric iodonium salts
2e–h were used, except for the main products (entries 5–8), less than 2%
by-products were found. It is known that four phenyl groups of sodium tetra-
phenylborate can participate in the coupling reaction. However, all yields are
not beyond 100%.
Taking advantage of these results, we further checked the reaction of
sodium tetraphenylborate with iodanes, which are less used in Suzuki
coupling reactions.[4a,7] We found that when equal equivalents of sodium tet-
raphenylborate with a readily available iodane PhI(OH)OTs,[8] referred to as
Koser’s reagent, as well as a small amount (0.2 mol%) of palladium chloride
as catalyst were added in water and microwave irradiated for 20 s, biphenyl
in 63% yield was afforded. To improve the yield, we changed Koser’s
reagent to 2 equivalents and 4 equivalents respectively under the same
reaction conditions; both reactions gave the near same yield (80%) of
biphenyl. Using 2 equivalents iodanes (4), we investigated the reactions of
them with 1 equivalent of sodium tetraphenylborate (1) and 0.2 mol%
palladium chloride as catalyst in water under microwave irradiation as

1498
J. Yan, Z. Zhou, and M. Zhu
Scheme 2.
shown in Scheme 2; we found that these reactions occurred smoothly. The
good results are recorded in Table 2. The products were characterized by
1H NMR, IR, MS spectra, and melting points, which were consistent with
the literature data.
It is obvious from Table 2 that hypervalent iodanes can be used as
powerful electrophilic agents in the Suzuki reaction although some yields
are somewhat low (entries 1 and 6) compared with the yields in Table 1. It
is well known that iodonium salts have been widely used in Suzuki
reactions. However, using iodanes in the coupling reactions were few, and
to our knowledge they have been no reports about base-free Suzuki
reactions of sodium tetraphenylborate with iodonium salts and iodanes in
water under microwave irradiation.
In summary, a rapid and efficient method for formation of carbon–carbon
bonds is afforded by the microwave-promoted base-free Suzuki reaction in
Table 2. Results of the coupling reaction of sodium tetraphenylborate with
iodanes under microwave irradiation
Entry
1
Iodane
Product
Yielda (%)
3a
80
4a
PhI(OAc)2
4b
2
3
4
5
3a
3a
3a
3a
99
89
91
93
PhI(OCOCF3)2
4c
Phl55O
4d
Ph-lþ-O-Iþ-Ph 2BF4
4e
6
78
3i
4f
aIsolated yield.

Rapid Microwave-Promoted Suzuki Reaction
1499
water medium. It is simple and fast and affords excellent yield. Furthermore,
the useful range of hypervalent iodine compounds in organic syntheses has
been extended.
EXPERIMENTAL
Melting points were determined on a digital melting-point apparatus and were
not corrected. IR spectra were recorded on a FT-170 SX instrument, 1H NMR
spectra were measured on a Bruker AM-400 FT-NMR spectrometer, and mass
spectra were determined on HP5989A mass spectrometer. Microwave
irradiation was carried out with an LWMC-201 domestic microwave oven
at 50% full power (650 W). Diphenyliodonium chloride (2a),[9] di(p-tolyl)
iodonium bromide (2b),[9] di(p-bromophenyl)iodonium bromide (2c),[10]
di(m-nitrophenyl) iodonium bromide (2d),[10] (p-methoxyphenyl)(phenyl)
iodonium bromide (2e),[9] 2-thienyl (phenyl)iodonium tosylate (2f),[11] alky-
nyliodonium salt (2g),[12] and alkenylliodonium salt (2h)[12] were prepared
according to the literature procedures. Hydroxy(tosyloxy)iodobenzene
(4a),[8] (diacetoxyiodo)benzene (4b),[13] [bis(tifluoroacetoxy)iodo]benzene
(4c),[14] iodosylbenzene (4d),[15] iodosobenzene tetrafluoroborate (4e),[16]
and 1-hydroxy-1,2-benziodoxol-3(1H)-one (4f)[17] were prepared according
to the literature procedures. Sodium tetraphenylborate is commercially
available.
Reaction of Sodium Tetraphenylborate with Iodonium Salts,
General Procedure
Sodium tetraphenylborate (1) (85.5 mg, 0.25 mmol, 1.0 equiv), iodonium salt
(2) (0.25 mmol, 1.0 equiv), palladium chloride (0.1 mg, 0.2% mmol), and
5 mL of H2O were placed in a glass tube inside a beaker and irradiated for
20 s in a domestic microwave oven at 50% full power (650 W). After
cooling to room temperature, the mixture was extracted with diethyl ether
(20 mL ꢀ 3), and the organic layer was dried over anhydrous MgSO4 and
evaporated in vacuo. The crude product was separated by a silica-gel plate
to give the products 3 in good yield.
Reaction of Sodium Tetraphenylborate with Iodanes,
General Procedure
Sodium tetraphenylborate (1) (85.5 mg, 0.25 mmol, 1.0 equiv), iodane (4)
(0.5 mmol, 2.0 equiv), palladium chloride (0.1 mg, 0.2% mmol), and 5 mL
of H2O were placed in a glass tube inside a beaker and irradiated for 20 s in
a domestic microwave oven at 50% full power (650 W). After cooling to

1500
J. Yan, Z. Zhou, and M. Zhu
room temperature, the mixture was extracted with diethyl ether (20 mL ꢀ 3),
and the organic layer was dried over anhydrous MgSO4 and evaporated in
vacuo. The crude product was separated by a silica-gel plate to give the
products 3 in good yield.
Data
Biphenyl (3a)
1
Mp 68–698C (lit.[18] 69–728C). H NMR (CDCl3): d ¼ 7.35 (m, 2H), 7.44
(m, 4H), 7.60 (m, 4H); IR (KBr): n ¼ 3035, 1569, 1481, 730 cm21; MS
(70eV, EI) m/z (%): 154 (Mþ, 100).
p-Methylbiphenyl (3b)
1
Mp 43–468C (lit.[19] 44–478C). H NMR (CDCl3): d ¼ 2.39 (s, 3H), 7.25
(m, 2H), 7.32 (m, 1H), 7.42 (m, 2H), 7.49 (m, 2H), 7.57 (m, 2H); IR (KBr):
n ¼ 3067, 3033, 1488, 1007, 823, 766, 690 cm21; MS (70eV, EI) m/z (%):
168 (Mþ, 100).
p-Bromobiphenyl (3c)
1
Mp 83–858C (lit.[19] 85–878C). H NMR (CDCl3): d ¼ 7.35 (m, 1H), 7.43
(m, 4H), 7.54 (m, 4H); IR (KBr): n ¼ 3064, 3031, 1477, 1393, 1080, 830,
767, 691 cm21; MS (75eV, EI) m/z (%): 234 (M þ 1), 233 (Mþ, 13.3), 232
(100).
m-Nitrobiphenyl (3d)
1
Mp 56–588C (lit.[19] 58–608C). H NMR (CDCl3): d ¼ 7.44–7.58 (m, 6H),
7.88 (m, 1H), 8.17 (m, 1H), 8.42 (m, 1H); IR (KBr): n ¼ 3064, 3036, 1536,
1362, 877, 772, 733 cm21; MS (75eV, EI) m/z (%): 199 (Mþ, 100).
p-Methoxylbiphenyl (3e)
Mp. 86–878C (lit.[19] 888C). 1H NMR (CDCl3): d ¼ 3.83 (s, 3H), 6.97
(m, 2H), 7.29 (m, 1H), 7.41 (m, 2H), 7.53 (m, 4H); IR (KBr): n ¼ 3068,
3033, 1262, 1035, 835, 761 cm21; MS (70eV, EI) m/z (%): 184 (Mþ, 100).
2-Phenylthiophene (3f)
Oil.[4a] 1H NMR (CDCl3): d ¼ 7.10 (m, 1H), 7.30–7.34 (m, 2H), 7.39
(m, 1H), 7.47 (m, 2H), 7.63 (m, 2H); IR (KBr) n ¼ 3103, 3062, 3036, 1496,
1451, 747 cm21; MS (70eV, EI) m/z (%): 160 (Mþ, 100).

Rapid Microwave-Promoted Suzuki Reaction
1501
Diphenylacetylene (3g)
Mp 58–598C (lit.[4a] 608C). 1H NMR (CDCl3): d ¼ 7.22–7.41 (m, 6H), 7.51
(m, 4H); IR (KBr): n ¼ 3064, 3032, 1600, 1500, 1262, 757, 691 cm21; MS
(75eV, EI) m/z (%): 178 (Mþ, 100).
E-1,2-Diphenylethylene (3h)
1
Mp 120–1218C (lit.[4a] 122–1248C). H NMR (CDCl3): d ¼ 7.15 (s, 2H),
7.21 (m, 2H), 7.34 (m, 4H), 7.48 (m, 4H); IR (KBr): n ¼ 3079, 3034, 1698,
1496, 1073, 966, 767, 693 cm21; MS (75eV, EI) m/z (%): 180 (Mþ, 100).
2-Biphenycarboxylic Acid (3i)
1
Mp 108–1108C (lit.[20] 1128C). H NMR (CDCl3): d ¼ 7.30–7.39 (m, 7H),
7.53 (m, 1H), 7.93 (m, 1H), 11.0 (br, 1H); IR (KBr): n ¼ 3400–2400 (br),
1700, 1685, 1306, 1296 cm21; MS (70eV, EI) m/z (%): 198 (Mþ, 100).
ACKNOWLEDGMENT
Financial support from the Zhejiang Province Natural Science Foundation of
China (Project Y404016) and Zhejiang Province Education Foundation of
China (Project 20040569) is greatly appreciated.
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