Suzuki-type cross-coupling reaction of pentavalent triarylantimony diacetates with arylboronic acids without a base

Article abstract of DOI:10.1016/j.tetlet.2006.10.163

Novel base-free Suzuki-type cross-coupling reaction by the use of triarylantimony diacetates and arylboronic acids in the presence of Pd(PPh₃)₄ catalyst led to the formation of biaryl derivatives in moderate to excellent yields. The reaction is applicable to a variety of arylboronic acids bearing base-sensitive functional groups.

Full text of DOI:10.1016/j.tetlet.2006.10.163

Tetrahedron Letters 48 (2007) 721–724
Suzuki-type cross-coupling reaction of pentavalent triarylantimony
diacetates with arylboronic acids without a base
a,b
a
a
a,
*
Shuji Yasuike, Weiwei Qin, Yoshiyuki Sugawara and Jyoji Kurita
a
Faculty of Pharmaceutical Sciences, Hokuriku University, Kanagawa-machi, Kanazsawa 920-1181, Japan
b
Organization for Frontier Research in Preventive Pharmaceutical Sciences, Hokuriku University,
Kanagawa-machi, Kanazsawa 920-1181, Japan
Received 24 October 2006; accepted 30 October 2006
Available online 11 December 2006
Abstract—Novel base-free Suzuki-type cross-coupling reaction by the use of triarylantimony diacetates and arylboronic acids in the
presence of Pd(PPh
a variety of arylboronic acids bearing base-sensitive functional groups.
2006 Elsevier Ltd. All rights reserved.
3 4
) catalyst led to the formation of biaryl derivatives in moderate to excellent yields. The reaction is applicable to
ꢀ
The Suzuki–Miyaura cross-coupling reaction is one of
the most versatile and utilized reactions for carbon–
carbon bond formation, in particular for the synthesis
pounds, triphenylantimony diacetate, with a variety of
arylboronic acids.
1
of biaryls. In these reactions, however, it is inevitable
We initially focused our attention on the determination
of the best experimental conditions for the cross-cou-
pling of organoantimony compounds 1a–c with p-methyl-
phenylboronic acid 3a without any bases. The results
including the search for active substrates and suitable
catalysts for the reaction are summarized in Table 1.
The progress of the reaction was monitored by gas–
liquid chromatography (GLC) and the reaction time
was determined when the yields of products 4a and 5
show a maximum value because it is impossible to detect
the disappearance of the starting material by thin-layer
chromatography (TLC) or GLC. First, we performed
the reaction of 3a (3 equiv) and antimony derivatives,
such as triphenylantimony 1a, triphenylantimony
to add a stoichiometric or excess amount of bases for
smooth transformation, which makes it difficult to apply
the reaction to base-sensitive substrates and, moreover,
the formation of an equivalent amount of waste salts
is unavoidable. Consequently, the development of
transition metal-catalyzed cross-coupling reactions of
organoboron compounds without bases has been a
challenging and urgent issue.2,3 On the other hand, tran-
sition metal-catalyzed coupling reaction by the use of
organoantimony compounds has recently been the focus
of attention. Among these compounds, pentavalent tri-
arylantimony dichloride and diacetate were known to
be effective in carbon–carbon bond formation such as
4
5
6
4b
Heck-, Stille-, and Hiyama-type cross-coupling reac-
tions. We have recently reported that the reaction of
organoantimony(III) compounds with acid halides, aryl
halides, and vinyl halides in the presence of Pd-catalyst
resulted in cross-coupling reaction to give alkynyl
dichloride 1b, and diacetate 1c, to compare the reactiv-
ity using 5 mol % of Pd(OAc) as a catalyst in 1,4-diox-
2
ane at 60 ꢁC (entries 1–3). The expected cross-coupling
compound 4a was obtained in a good yield along with
homo-coupling product 5 when 1c was employed as a
substrate. In this reaction, one of the three phenyl
groups on antimony is involved in the carbon–carbon
bond formation. On the other hand, pentavalent dichlo-
ride 1b was found to be less reactive toward the cross-
coupling reaction and the major product was biphenyl
7
ketones, diarylacetylenes, and enyne compounds. We
present here a novel base-free Pd-catalyzed Suzuki-type
cross-coupling reaction of organoantimony(V) com-
5
formed by the homo-coupling reaction of phenyl
Keywords: Base-free; Suzuki-type cross-coupling; Antimony; Triphen-
group on 1b. It is also known that pentavalent triaryl-
bismuth dichloride 2b and diacetate 2c were effective
reagents as a pseudo-halogen compound in carbon–carbon
ylantimony diacetate; Palladium; Biaryl.
*
Corresponding author. Tel.: +81 76 229 1165; fax: +81 76 229
781; e-mail: j-kurita@hokuriku-u.ac.jp
2
0040-4039/$ - see front matter ꢀ 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2006.10.163

722
S. Yasuike et al. / Tetrahedron Letters 48 (2007) 721–724
Table 1. Palladium-catalyzed Suzuki-type cross-coupling reaction of organo-antimony 1 and -bismuth 2 compounds with 4-methylphenyllboronic
a
acid 3a
OH
X
H C
3
B
3a
Ph
Ph
OH
M
Ph
CH3
+
Pd cat.
X
Dioxane, 60 °C
1
2
: M = Sb
: M = Bi
4a
5
b,c
Entry
Substrate
M
X
Pd cat.
Time (h)
Yield
4
a
5
1
2
3
4
5
6
7
8
9
1a
1b
1c
2a
2b
2c
1c
1c
1c
1c
1c
1c
1c
Sb(III)
Sb(V)
Sb(V)
Bi(III)
Bi(V)
Bi(V)
Sb(V)
Sb(V)
Sb(V)
Sb(V)
Sb(V)
Sb(V)
Sb(V)
—
Cl
OAc
—
Cl
OAc
OAc
OAc
OAc
OAc
OAc
OAc
OAc
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
Pd(OAc)
2
2
2
2
2
2
12
12
12
12
12
12
12
12
12
6
ND
8
92
6
ND
84
6
26
122
97
3
2
4
ND (0)
5
ND
ND
3
39
60
95
73
98 (94)
91
95
PdCl
PdCl
2
2
(PPh
3
)
2
Pd(dba)
2
f
1
1
1
1
0
1
2
3
Pd(PPh
Pd(PPh
Pd(PPh
None
3
)
)
)
4
4
4
d
e
3
3
36
36
36
ND
a
Compound 1 or 2 (0.5 mmol), 3a (1.5 mmol), Pd cat. (5 mol %).
The yields of 4a and 5 were determined by GLC using tetradecane or octadecane as an internal standard, and the yield 100% correspond to the
b
involvement of one phenyl group on 1 or 2.
ND: not detected.
Compound 3a (0.75 mmol).
Pd cat. (1 mol %).
c
d
e
f
Isolated yield.
8
9
bond formation such as Heck- and Stille-type cross-
coupling reactions. However, the homo-coupling reac-
tion took precedence over the expected cross-coupling
reaction when bismuth agents 2a–c were used instead
of antimony reagents in the present reaction (entries
Similar reactions by the use of tri(p-tolyl)antimony
4
b
diacetate [(p-CH C H ) Sb(OAc) ] and tri(p-chloro-
3
6
4 3
2
1
0
phenyl)antimony diacetate [(p-ClC H ) Sb(OAc) ]
with 3a afforded 4,4 -dimethylbiphenyl (96%) and
4-chloro-4 -methylbiphenyl 4f (93%) in good yields
6
4 3
2
0
0
4
–6). These results showed that the reactivity of the
(60 ꢁC, 6 h), respectively.
metal reagents was considerably affected by not only
the valence [(III), (V)] and the kind (Sb, Bi) of the con-
stitutive metal, but also the substituent (Cl, OAc) on the
metal. Next, several available palladium catalysts were
also screened by means of the reaction between 1c and
The scope of the present coupling was evaluated by inves-
tigating the reaction of 3a with a variety of arylboronic
1
1
acids 3b–o. The reaction was carried out for 6 h for
3b–d bearing an electron-donating group and for 18 h
for 3f–m having an electron-withdrawing group, because
the reaction rate was sensitive to the electronic nature of
the acids and the decrease of 1c in the course of the reac-
tion could not be monitored by TLC and GLC as noted
above (Table 2). Thus, 3b–d afforded the corresponding
cross-coupling product 4b–d in good yields in a shorter
reaction time (6 h, entries 1–3), while 3f–m gave 4f–m
in satisfactory yields in a longer reaction time (18 h, en-
tries 5–12). The results also showed that the present
base-free reaction allows employment of acids 3i,j, and
3l with a relatively base-sensitive group. Moreover, the
reaction can be applied to the cross-coupling-active sub-
strate, 2-bromophenylbronic acid 3g, whose carbon–
bromine bond remained intact (entry 6). Additionally,
the reaction of heterocyclic boronic acids 3n and 3o
gave the corresponding biaryls 4n and 4o, respectively
(entries 13 and 14). Unfortunately, sterically hindered
2,6-dimethylphenylboronic acid and basic 4-pyridyl-
boronic acid did not afford cross-coupling products.
3
4
a (entries 3, 7–10). All catalysts examined here afforded
a in good yields. Among these, Pd(PPh ) appeared to
3
4
be the best catalyst for this reaction in terms of the yield
98%) of the cross-coupling product 4a and reaction
time (6 h), and no homo-coupling product 5 was formed
entry 10). When the reaction was carried out at rt, 4a
(
(
was formed in 41% yield after 24 h. We also tested the
reaction without a palladium catalyst, but the formation
of coupling products 4a and 5 was not detected by GLC
analysis (entry 13). When loading of boron reagent
(
1.5 equiv, entry 11) and catalyst (1 mol %, entry 12)
was decreased, prolonged time was required to finish
the reaction and the formation of 5 was observed in
the former reaction. Utilization of other solvents such
as toluene (44%) and 5:1 mixture of dioxane–water
(
5%) gave inferior results under the same reaction condi-
tions (60 ꢁC, 6 h). Consequently, the best result was
obtained when 1c was treated with 3a (3 equiv) by the
use of Pd(PPh3)4 (5 mol %) in 1,4-dioxane at 60 ꢁC.

S. Yasuike et al. / Tetrahedron Letters 48 (2007) 721–724
723
a
Table 2. Base-free palladium-catalyzed Suzuki-type cross-coupling reaction of triphenylantimony diacetate 1c with arylboronic acids 3
OH
OAc
Ar
B
3
Ph
Ph
OH
Sb Ph
OAc
Ph Ar
Pd(PPh3)4
Dioxane, 60 °C
1c
4
b
Entry
ArB(OH)
2
Time (h)
Product
Yield (%)
1
2
3
4
5
6
7
8
9
0
1
2
3
4
3,4-(Methylenedioxy)phenyl 3b
4-t-Butylphenyl 3c
4-Methoxyphenyl 3d
1-Naphthyl 3e
4-Chlorophenyl 3f
2-Bromophenyl 3g
4-Formylphenyl 3h
4-(Methoxycarbonyl)phenyl 3i
4-Acetylphenyl 3j
4-(Trifluoromethyl)phenyl 3k
4-Cyanophenyl 3l
6
6
6
4b
4c
4d
4e
4f
95
96
92
97
6
c
18
18
18
18
18
18
18
18
6
98 (55)
4g
4h
4i
95
82
85
88
83
71 (32)
65 (30)
96
88
4j
1
1
1
1
1
4k
4l
c
c
4-Nitrophenyl 3m
2-Benzothienyl 3n
2-Benzofuryl 3o
4m
4n
4o
6
a
b
c
3 4
Compound 1 (0.5 mmol), 3a (1.5 mmol), Pd(PPh ) (5 mol %).
Isolated yield (the yield 100% correspond to the involvement of one phenyl group on 1c).
Reaction time, 6 h.
A plausible mechanism of the present base-free Suzuki-
type cross-coupling reaction is depicted in Scheme 1. As
reported by Gushchin and co-workers, the initial step
of this reaction should involve oxidative addition of the
mony by constructing a six-membered ring B.12 This
interpretation should be also supported by the following
facts. The antimony compounds (Ph Sb, Ph SbCl )
4
b
3
3
2
without an acetoxy group on the antimony are ineffec-
tive (Table 1, entries 1 and 2). In addition, the aryl-
boronic ester, 5,5-dimethyl-2-p-tolyl-1,3,2-dioxaborinane
which has no ability to form the six-membered inter-
mediate B was ineffective in the present reaction under
Ar–Sb bond of 1c onto the L Pd(0) species. Taking into
2
account the results that the reaction does not need a
base as an additive for the activation of boronic acid,
the formation of intermediate B with B---O and
OH---O inter-coordination is anticipated from A and
boronic acids 3. In intermediate B, the boronic acid moi-
ety should be activated by the acetoxy group on the anti-
1
3
the same conditions. Pentavalent organoantimony(V)
compounds were well known to be reduced to Sb(III)
1
4
compounds with ease. As a result, diorganopalladium
complex E thus formed via intermediate B undergoes
reductive elimination to give coupling products 4 and
reproduces the Pd(0) species.
PdL4
In summary, we have found that triphenylantimony
diacetate is an efficient substrate in palladium-catalyzed
cross-coupling reactions with arylboronic acids, which
can be conducted under mild conditions without any
bases. Various boronic acids having electron-donating
or -withdrawing functional groups afforded the corres-
ponding cross-coupling product in 65–98% yields.
Organoantimony(V) compound 1 is a new class of
pseudo-halogen compound for base-free Suzuki-type
cross-coupling reaction. Synthetic application of this
reaction and work on the detailed reaction mechanism
are in progress.
OAc
Ph
Ph Sb
Ph Ar
4
Ph
OAc
PdL2
1c
L
Ph Pd Ar
L
OAc
Ph
Ph Pd Sb
L
Ph
E
L
OAc
A
H
O
Ar B(OH)2
O
Ph SbOAc
C
D
2
HO
3
Acknowledgements
+
B
Ar
O
Me
AcOB(OH)2
Ph
This work was financially supported by a Grant-in Aid
for Scientific Research (C) from the Ministry of Educa-
tion, Culture, Sports, Sciences, and Technology of
Japan (to J.K.); the ‘Academic Frontier’ Project for
Private Universities from the Ministry of Education,
Ph Pd Sb
Ln
Ph
OAc
B
Scheme 1. Proposed mechanism.

724
S. Yasuike et al. / Tetrahedron Letters 48 (2007) 721–724
Culture, Sports, Sciences, and Technology of Japan
to S.Y.); the Sasakawa Scientific Research Grant from
the Japan Science Society (to W.Q.); and the Specific
Research Fund of Hokuriku University, which is grate-
fully acknowledged.
2953–2968; (b) Kakusawa, N.; Yamaguchi, K.; Kurita, J.
J. Organomet. Chem. 2005, 690, 2956–2966; (c) Kakusawa,
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(
8
. Moiseev, D. V.; Malysheva, Y. B.; Shavyrin, A. S.;
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2
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9. Kang, S.-K.; Ryu, H.-C.; Lee, S.-W. Synth. Commun.
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References and notes
2
1
. (a) Suzuki, A.; Brown, H. C. In Organic Synthesis via
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10. Preparation and structural data of tri(p-chlorophenyl)anti-
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(2.0 mmol) and (diacetoxyiodo)benzene (2.2 mmol) in
dichloromethane (CH Cl : 10 mL) was stirred for 24 h at
2 2
1
469; (c) Kotha, S.; Lahiri, K.; Kashinath, D. Tetrahedron
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2
. Cross-coupling reaction for biaryls with boron reagents
without base (a) Yan, J.; Zhu, M.; Zhou, Z. Eur. J. Org.
Chem. 2006, 2060–2062; (b) Yan, J.; Zhou, Z.; Zhu, M.
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2 2
give tri(p-chlorophenyl)antimony diacetate 0.81 g (71%) as
1
colorless prisms, mp 117–120 ꢁC. H NMR (400 MHz,
CDCl ): d 1.83 (6H, s), 7.46 (6H, d, J = 8.7 Hz), 7.88 (6H,
3
13
d, J = 8.7 Hz); C NMR (100 MHz, CDCl ): d 21.7 (s),
3
129.4 (d), 135.0 (d), 137.6 (s, ·2), 176.8 (s); MS (EI) m/z:
+
ꢀ1
515 (MꢀOAc) ; IR (KBr): 1633 cm
(C@O). Anal.
Calcd for C22H O Cl Sb: C, 45.99; H, 3.16. Found: C,
18 4 3
3
. Cross-coupling reaction with boron reagents without base
46.08; H, 3.29.
(
2
a) Tsukamoto, H.; Sato, M.; Kondo, Y. Chem. Commun.
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11. Typical experiment: A solution of triphenylantimony
diacetate 1c (0.5 mmol), arylboronic acids 3 (1.5 mmol),
and tetrakis(triphenylphosphine)palladium (0.025 mmol)
in 1,4-dioxane (3 mL) was heated at 60 ꢁC for 6–18 h
under an argon atmosphere. After dilution with ether
(40 mL) and water (20 mL), the reaction mixture was
separated and the aqueous layer was extracted with ether
(20 mL). The combined organic layer was washed with
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Strijdonck, G.-P. F. Tetrahedron Lett. 2004, 45, 7659–
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4
water, dried over anhydrous MgSO , and concentrated
under reduced pressure. The crude residue was purified by
short column chromatograph on silica gel with hexane (for
(
g) Savarin, C.; Srogl, J.; Liebeskind, L. S. Org. Lett. 2001,
, 91–93.
3
2 2
4a,c,e–g) or hexane–CH Cl (for 4b,d,h–o) to give biaryl
4
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Shavirin, A. S.; Kursky, Y. A.; Dodonov, V. A. J.
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derivatives 4. The structure of the products was confirmed
by comparison of the NMR and MS spectral data with
that in the literature.
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3 4
(1.5 mmol), 1c (0.5 mmol), and Pd(PPh ) (5 mol %) in
dioxane (3 mL) was heated at 60 ꢁC for 18 h. This reaction
gave 4a (9%) and arylboronic ester (75%, recovery) by
separation.
2
000, 3350–3351.
. Kang, S.-K.; Ryu, H.-C.; Lee, S.-W. J. Organomet. Chem.
000, 610, 38–41.
5
6
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