Pd(OAc)2/DABCO as an inexpensive and efficient catalytic system for Hiyama cross-coupling reactions of aryl halides with aryltrimethoxysilanes

Article abstract of DOI:10.1055/s-2005-918411

Pd(OAc)₂/DABCO was found to be an inexpensive and efficient catalyst system for Hiyama cross-coupling reactions of aryl halides with aryltrimethoxysilanes. In the presence of Pd(OAc)₂, DABCO, and TBAF, coupling of a number of aryl halides with aryltrimethoxysilanes underwent efficiently to afford the corresponding cross-coupled products in moderate to excellent yields. Georg Thieme Verlag Stuttgart.

Full text of DOI:10.1055/s-2005-918411

PAPER
3039
Pd(OAc)2/DABCO as an Inexpensive and Efficient Catalytic System for
Hiyama Cross-Coupling Reactions of Aryl Halides with Aryltrimethoxysilanes
P
d(OAc
)
/
2i
D
A
BC
n
OCatalytic
-
f
H
or
H
iyama Cross-C
e
oupling ng Li,* Chen-Liang Deng, Wen-Jie Liu, Ye-Xiang Xie
Key Laboratory of Chemical Biology & Traditional Chinese Medicine Research, College of Chemistry and Chemical Engineering, Hunan
Normal University, Changsha 410081, P. R. of China
Fax +86(731)8872260; E-mail: jhli@hunnu.edu.cn
Received 10 May 2005; revised 15 June 2005
Pd(OAc)2/DABCO
+
X
Abstract: Pd(OAc)2/DABCO was found to be an inexpensive and
efficient catalyst system for Hiyama cross-coupling reactions of
aryl halides with aryltrimethoxysilanes. In the presence of
Pd(OAc)2, DABCO, and TBAF, coupling of a number of aryl ha-
lides with aryltrimethoxysilanes underwent efficiently to afford the
corresponding cross-coupled products in moderate to excellent
yields.
ArSi(OMe)3
Ar
TBAF, dioxane, 80 °C
R
R
1
2
3–15
X = I, Br, Cl
Equation 1
Efficiency of Pd(OAc)2/DABCO as the catalyst system
for coupling of 1-bromo-4-methoxybenzene (1a) with
phenyltrimethoxysilane (2a) was evaluated, and the re-
sults are summarized in Table 1. Initially, a series of ter-
tiary amines as ligands were tested (entries 1–5). The
results showed that DABCO as the ligand was the most ef-
fective, and the amount of DABCO affected the yield to
some extent. In the presence of 3 mol% of Pd(OAc)2, 6
mol% DABCO, and 2 equivalents of TBAF, a 72% yield
of the corresponding coupled product 3 was obtained in
four hours (entry 5), whereas the yield decreased slightly
to 67% when 3 mol% of DABCO was used (entry 6). In
the presence of 12 mol% of DABCO, 70% yield of 3 was
isolated after four hours (entry 7). A set of solvents, such
as dioxane, THF, MeCN, acetone and DMF, were then ex-
amined, and dioxane as the solvent afforded the highest
yield (entries 5 and 8–11). Finally, some bases including
TBAF, KF, and K2CO3 were also investigated, and TBAF
as the base gave the best results (entries 4, 12 and 13).
Key words: Pd(OAc)2, DABCO, Hiyama cross-coupling reaction,
aryl halide, aryltrimethoxysilane
Because biaryls are a recurring functional group in a wide
range of natural products and other biologically active
compounds, and are valuable intermediates in organic
synthesis.1 For these reasons, many selective and efficient
methods including the palladium-catalyzed cross-cou-
pling reactions have been developed for the synthesis of
biaryls.2–6,7a,c Recently, much attention has been attracted
on the use of silicon-derived compounds as alternative re-
agents for the cross-coupling transformations (the Hiya-
ma cross-coupling reaction) due to their easy availability
and/or low toxicity.4–6 However, few efficient catalytic
systems have been developed for the palladium-catalyzed
Hiyama cross-coupling reaction. Generally, high catalyst
and phosphine loadings are required to give high yields
for unactivated aryl halides.5 Recently, Nolan and Lee
have reported an efficient Hiyama cross-coupling reaction
of unactivated aryl halides with phenylsilane or vinylsi-
lane under a rather low catalyst loading [3 mol% of
Pd(OAc)2 and 3 mol% of imidazolium chloride].6 Howev-
er, imidazolium chloride as well as the reported phosphine
ligands are also expensive. Thus, the development of an
inexpensive and efficient catalytic system for the Hiyama
cross-coupling reaction is still an important objective.
Very recently, we have demonstrated DABCO as an effi-
cient ligand for the palladium-catalyzed Suzuki–
Miyaura,7a Sonogashira,7b and Stille cross-coupling reac-
tions.7c As an extension of this work, we report herein
Pd(OAc)2/DABCO as an inexpensive and efficient cata-
lytic system for the Hiyama cross-coupling reactions of
aryl halides with aryltrimethoxysilanes (Equation 1).
As shown in Table 2, Pd(OAc)2/DABCO is an efficient
catalyst system for the Hiyama cross-coupling reactions
of various aryl halides 1a–p with aryltrimethoxysilanes
2a–d. The results demonstrated that coupling of bromide
1a with other silanes 2b and 2c, respectively, could be
also carried out smoothly to afford moderate yields of the
corresponding products in the presence of 3 mol% of
Pd(OAc)2, 6 mol% of DABCO and 3 equiv of TBAF
(Table 2, entries 2 and 3). It is noteworthy that moderate
yield was still observed after prolonged reaction time
when 5 mol of 1a was coupled with 8 mol of 2a (entry 1).
Under the similar reaction conditions, treatment of aryl io-
dides 1b–e with silane 2a, respectively, gave the corre-
sponding cross-coupled products in excellent yields
(entries 4–7). The results indicated that the efficiency of
the Pd(OAc)2/DABCO catalytic system for the reactions
of aryl bromides was decreased to some extent. Aryl io-
dides could be consumed completely in one hour (entries
4–7), whereas more than four hours were required for the
complete conversion of aryl bromides (entries 1–3 and 8–
SYNTHESIS 2005, No. 18, pp 3039–3044
x
x.
x
x
.
2
0
0
5
Advanced online publication: 29.09.2005
DOI: 10.1055/s-2005-918411; Art ID: F08405SS
© Georg Thieme Verlag Stuttgart · New York

3040
J.-H. Li et al.
PAPER
Table 1 Pd(OAc)2/DABCO-Catalyzed Cross-Coupling of 1-Bro-
mo-4-methoxybenzene (1a) with Phenyltrimethoxysilane (2a)a
18). In the presence of 3 mol% of Pd(OAc)2 and 6 mol%
of DABCO, aryl bromides 1f–k were coupled with silanes
2a–d, respectively, to give moderate to good yields. For
example, treatment of bromobenzene 1h with 2a–d, re-
spectively, afforded good yields of the corresponding
products (entries 11–14). It is interesting to note that the
Pd(OAc)2/DABCO catalytic system is still effective for
the activated aryl halides 1j and 1k (entries 19–21). For
coupling of aryl chlorides 1n–p, however, low yields were
observed even at 100 °C (entries 22–25).
Pd(OAc)2/L
MeO
Br
+
PhSi(OMe)3
MeO
Ph
base, 80 °C
2a
3
1a
Entry
1
Ligand
Et3N
Base
Solvent
Yield (%)b
65
TBAF
TBAF
TBAF
TBAF
TBAF
TBAF
TBAF
TBAF
TBAF
TBAF
TBAF
KF
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
dioxane
THF
2
TMEDA
HMPA
trace
trace
35
The catalytic efficacy of the Pd(OAc)2/DABCO catalytic
system for the Hiyama reaction was further evaluated, and
the results are summarized in Table 3. For coupling of the
activated aryl bromide 1f with silanes 2a and 2b, respec-
tively, the catalyst loadings could be decreased to 0.1
mol%, and good yields were obtained after prolonged
heating (entries 3 and 6). A moderate yield was still iso-
lated when the Pd loading was deceased to 0.01 mol%
(entry 4). However, a low yield was observed when the Pd
loading was further decreased to 0.001 mol% (entry 5).
For coupling of the deactivated aryl bromide 1a with 2a,
the catalytic efficiency decreased to some extent (entries
1 and 2). The results showed that the suitable Pd loading
for the reaction of 1i was 1 mol%. It is noteworthy that
coupling of the activated aryl chloride 1l with 2a still af-
fords a desirable yield in the presence of 0.1 mol% Pd (en-
try 7). Further decrease of the catalyst loading to 0.01
mol% led to low yield (32%, entry 8).
3
4
DBU
5
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
DABCO
72
6c
7d
8e
9
67
70
31
MeCN
acetone
DMF
44
10
11
12
13
68
31
dioxane
dioxane
trace
trace
K2CO3
a Reaction conditions: 1a (0.5 mmol), 2a (1.0 mmol), Pd(OAc)2 (3
mol%), ligand (6 mol%), base (2 equiv), and solvent (3 mL) at 80 °C
for 4 h.
b Isolated yield.
c DABCO (3 mol%).
d DABCO (12 mol%).
e For 11 h.
Table 2 Pd(OAc)2/DABCO-Catalyzed Cross-Coupling of Aryl Halides with Aryltrimethoxysilanea
Pd(OAc)2/DABCO
+
X
ArSi(OMe)3
Ar
TBAF, dioxane, 80 °C
R
R
1
2
3–15
Entry
1c
Aryl Halide
Silane
Time (h)
15
Product
Yield (%)b
75
3
Si(OMe)3
MeO
Br
2a
1a
1a
2
3
4
4
4
1
4
5
6
70
Me
2b
Si(OMe)3
1a
68
MeO
Si(OMe)3
2c
2a
~100
O2N
I
1b
Synthesis 2005, No. 18, 3039–3044 © Thieme Stuttgart · New York

PAPER
Pd(OAc)2/DABCO Catalytic System for Hiyama Cross-Coupling
3041
Table 2 Pd(OAc)2/DABCO-Catalyzed Cross-Coupling of Aryl Halides with Aryltrimethoxysilanea (continued)
Pd(OAc)2/DABCO
+
X
ArSi(OMe)3
Ar
TBAF, dioxane, 80 °C
R
R
1
2
3–15
Entry
5
Aryl Halide
Silane
Time (h)
1
Product
Yield (%)b
95
2a
7
I
NO2
1c
6
7
8
2a
2a
2a
1
1
4
8
3
6
91
94
93
I
1d
MeO
1e
I
O2N
Br
1f
1f
9
2b
2a
4
4
9
95
87
10
10
O
Br
1g
11
2a
4
8
83
Br
1h
1h
12
13
14
2b
2c
4
4
4
11
3
86
76
85
1h
1h
12
F
Si(OMe)3
2d
2a
15
4
11
81
Me
Br
1i
1i
16
17
2b
2c
4
13
14
80
72
12
Br
Me
1j
18
19
2a
2a
4
15
60
92
Me
Br
Me
1k
10
6
O2N
Cl
1l
1l
20
21
2b
2a
12
24
9
88
80
10
O
Cl
1m
Synthesis 2005, No. 18, 3039–3044 © Thieme Stuttgart · New York

3042
J.-H. Li et al.
PAPER
Table 2 Pd(OAc)2/DABCO-Catalyzed Cross-Coupling of Aryl Halides with Aryltrimethoxysilanea (continued)
Pd(OAc)2/DABCO
+
X
ArSi(OMe)3
Ar
TBAF, dioxane, 80 °C
R
R
1
2
3–15
Entry
22
Aryl Halide
Silane
Time (h)
24
Product
Yield (%)b
21
2a
8
Cl
1n
1n
23d
24d
2a
2a
24
24
8
45
34
11
Me
1o
Cl
25d
2a
24
3
20
MeO
Cl
1p
a Reaction conditions: 1 (0.5 mmol), 2 (1.0 mmol), Pd(OAc)2 (3 mol%), DABCO (6 mol%), TBAF (2 equiv), and dioxane (3 mL) at 80 °C.
b Isolated yield.
c 1a (5 mmol) and 2a (8 mmol).
d At 100 °C.
and dioxane (3 mL) was taken in a sealed tube. Then the mixture
was stirred at 80 °C for desired the time (Table 2) until complete
consumption of starting material as judged by TLC. After the mix-
ture was filtered and evaporated, the residue was purified by flash
column chromatography (hexane or hexane–EtOAc) to afford 3–15
(Table 2).
In summary, we have developed an inexpensive and high-
ly efficient Pd(OAc)2/DABCO catalytic system for the
Hiyama cross-coupling reactions of aryl halides with aryl-
trimethoxysilanes to construct biaryl units. Furthermore,
high TONs (turnover numbers, TONs up to 39,000 for the
reaction of 1-bromo-4-nitrobenzene with phenyltri-
methoxysilane) were observed for the Hiyama cross-cou-
pling reaction. Further efforts to apply this new protocol
in organic synthesis are in progress in our laboratory.
4-Methoxybiphenyl (3)5
1H NMR (400 MHz, CDCl3): d = 7.55 (t, J = 8.8 Hz, 4 H), 7.42 (t,
J = 8 Hz, 2 H), 7.31 (t, J = 7.2 Hz, 1 H), 6.99 (d, J = 12 Hz, 2 H),
1.57 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 159.1, 140.7, 133.7, 128.7, 128.1,
126.7, 126.6, 114.2, 55.3.
Palladium-Catalyzed Hiyama Cross-Coupling Reaction;
General Procedure
A mixture of aryl halide 1 (0.5 mmol), aryltrimethoxysilane 2 (1.0
mmol), Pd(OAc)2 (3 mol%), DABCO (6 mol%), TBAF (2 equiv),
Table 3 Screening of the Catalytic Efficiency of the Pd(OAc)2/DABCO Catalytic System for the Reactions of Aryl Halides with Aryltri-
methoxysilanesa
Entry
Aryl Halide
ArSi(OMe)3
Pd (mol%)
1
Time (h)
10
Product
Yield (%)b
TON
75
1
2
3
4
5
6
7
8
1a
1a
1f
1f
1f
1f
1l
2a
2a
2a
2a
2a
2b
2a
2a
3
3
6
6
6
9
6
6
75
5
0.1
48
50
0.1
24
85
59
39
81
62
32
850
0.01
0.001
0.1
48
5,900
39,000
810
48
24
0.1
60
620
1l
0.01
60
3 200
a Reaction conditions: 1 (0.5 mmol), 2 (1.0 mmol), Pd(OAc)2/DABCO (1: 2), TBAF (2 equiv), and dioxane (3 mL) at 80 °C.
b Isolated yield.
Synthesis 2005, No. 18, 3039–3044 © Thieme Stuttgart · New York

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Pd(OAc)2/DABCO Catalytic System for Hiyama Cross-Coupling
3043
4-Methyl-4¢-methoxybiphenyl (4)5
2-Methyl-4¢-methoxybiphenyl (14)5
1H NMR (400 MHz, CDCl3): d = 7.26–7.22 (m, 6 H), 6.95 (d,
J = 8.4 Hz, 2 H), 3.85 (s, 3 H), 2.28 (s, 3 H).
1H NMR (400 MHz, CDCl3): d = 7.50 (d, J = 8.8 Hz, 2 H), 7.44 (d,
J = 8.4 Hz, 2 H), 7.22 (d, J = 8.0 Hz, 2 H), 6.95 (d, J = 8.8 Hz, 2 H),
3.83 (s, 3 H), 2.37 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 158.5, 141.5, 135.5, 134.3, 130.3,
130.2, 129.9, 127.0, 125.8, 113.5, 55.3, 20.6.
13C NMR (100 MHz, CDCl3): d = 158.9, 137.9, 136.3, 133.7, 129.4,
127.9, 126.5, 114.1, 55.3, 21.0.
3,5-Dimethylbiphenyl (15)5,7a
4,4¢-Dimethoxybiphenyl (5)5
1H NMR (400 MHz, CDCl3): d = 7.46 (d, J = 8.8 Hz, 4 H), 6.94 (d,
J = 8.8 Hz, 4 H), 3.83 (s, 6 H).
1H NMR (400 MHz, CDCl3): d = 7.59 (d, J = 8.4 Hz, 2 H), 7.44–
7.40 (m, 2 H), 7.31–7.28 (m, 1 H), 7.19 (d, J = 8.4 Hz, 2 H), 6.98
(d, J = 9.2 Hz, 1 H), 2.35 (d, J = 8.6 Hz, 6 H).
13C NMR (100 MHz, CDCl3): d = 158.7, 133.5, 127.7, 114.1, 59.3.
13C NMR (100 MHz, CDCl3): d = 141.5, 138.1, 128.9, 128.7, 127.9,
127.2, 127.1, 125.1, 21.4.
4-Nitrobiphenyl (6)5
1H NMR (400 MHz, CDCl3): d = 8.31 (d, J = 8.4 Hz, 2 H), 7.75 (d,
J = 8.8 Hz, 2 H), 7.64 (d, J = 7.2 Hz, 2 H), 7.53–7.46 (m, 3 H).
Hiyama Cross-Coupling Reaction of 1-Bromo-4-nitrobenzene
(1f) and Phenyltrimethoxysilane (2a) at Low Catalyst Loading
(Table 3, Entry 4)
13C NMR (100 MHz, CDCl3): d = 147.6, 147.1, 138.8, 129.2,
128.91, 127.8, 127.4, 124.1.
Separate solutions of Pd(OAc)2 (4.5 mg, 0.02 mmol) in dioxane
(200 mL) and DABCO (4.5 mg, 0.04 mmol) in dioxane (200 mL)
were prepared first. Then 0.5 mL of Pd(OAc)2 dioxane solution and
0.5 mL of DABCO dioxane solution were added by syringe to a
mixture of 1-bromo-4-nitrobenzene (1d; 101 mg, 0.5 mmol), phe-
nyltrimethoxysilane (2a; 198 mg, 1.0 mmol), Bu4NF (523 mg, 2
equiv), and dioxane (2 mL) in a sealed tube. The mixture was stirred
at 80 °C for 48 h (TLC). After the mixture was filtered and evapo-
rated, the residue was purified by flash column chromatography
(hexane–EtOAc) to afford 6; yield: 59% (TONs: 5900).
2-Nitrobiphenyl (7)5
1H NMR (400 MHz, CDCl3): d = 7.86 (d, J = 8 Hz, 1 H), 7.62 (t,
J = 7.2 Hz, 1 H), 7.51–7.40 (m, 5 H), 7.34–7.31 (m, 2 H).
13C NMR (100 MHz, CDCl3): d = 163.7, 140.3, 137.3, 128.8, 128.7,
128.6, 127.3, 127.0, 115.7, 115.5.
Biphenyl (8)5
1H NMR (300 MHz, CDCl3): d = 7.59 (d, J = 8.4 Hz, 4 H), 7.43 (t,
J = 7.2 Hz, 4 H), 7.36 (t, J = 7.8 Hz, 2 H).
Acknowledgment
13C NMR (75 MHz, CDCl3): d = 141.6, 129.1, 127.6, 127.5.
We thank the National Natural Science Foundation of China (No.
20202002) for financial support.
4-Methyl-4¢-nitrobiphenyl (9)5
1H NMR (400 MHz, CDCl3): d = 8.27 (d, J = 8.8 Hz, 2 H), 7.71 (d,
J = 8.8 Hz, 2 H), 7.53 (d, J = 8.4 Hz, 2 H), 7.30 (d, J = 7.8 Hz, 2 H),
2.42 (s, 3 H).
References
13C NMR (100 MHz, CDCl3): d = 147.5, 146.7, 139.0, 135.7, 129.8,
127.4, 127.1, 124.0, 21.2.
(1) Bringmann, G.; Gunther, C.; Ochse, M.; Schupp, O.; Tasler,
S. Progress in the Chemistry of Organic Natural Products,
Vol. 82; Herz, W.; Falk, H.; Kirby, G. W.; Moore, R. E.,
Eds.; Springer: Berlin, 2001, 1–293.
(2) Hegedus, L. S. Organometallics in Synthesis; Schlosser, M.,
Ed.; Wiley: Chichester, 2002, 1123.
(3) For selected Ullmann coupling reactions, see:
(a) Brongmann, G.; Walter, R.; Weirich, R. Angew. Chem.,
Int. Ed. Engl. 1990, 29, 977. (b) Zhang, S.; Zhang, D.;
Liebeskind, L. S. J. Org. Chem. 1997, 62, 2312. (c) Li, J.-
H.; Xie, Y.-X.; Yin, D.-L. J. Org. Chem. 2003, 68, 986; and
references cited therein.
(4) For selected reviews on the Hiyama cross-coupling reaction,
see: (a) Diederich, F.; Stang, P. J. Metal-Catalyzed Cross-
Coupling Reactions; Wiley-VCH: Weinheim, 1998.
(b) Miyaura, N. Cross-Coupling Reaction; Springer: Berlin,
2002. (c) Chuit, C.; Corriu, R. J. P.; Reye, C.; Young, J. C.
Chem. Rev. 1993, 93, 1317. (d) Horn, K. A. Chem. Rev.
1995, 95, 1317.
(5) For recent selected papers on phosphine-palladium catalysts
for the Hiyama cross-coupling reaction, see: (a) Hatanaka,
Y.; Fukushima, S.; Hiyama, T. Chem. Lett. 1989, 1711.
(b) Hatanaka, Y.; Gouda, Y.; Okahara, T.; Hiyama, T.
Tetrahedron 1994, 50, 8301. (c) Gouda, K.; Hagiwara, E.;
Hatanaka, Y.; Hiyama, T. J. Org. Chem. 1996, 61, 7232.
(d) Hagiwara, E.; Gouda, K.; Hatanaka, Y.; Hiyama, T.
Tetrahedron Lett. 1997, 38, 439. (e) Mowery, M. E.;
DeShong, P. Org. Lett. 1999, 1, 2137. (f) Mowery, M. E.;
DeShong, P. J. Org. Chem. 1999, 64, 1684. (g) Mowery,
1-Biphenyl-4-ylethanone (10)5
1H NMR (400 MHz, CDCl3): d = 8.04 (d, J = 8.4 Hz, 2 H), 7.69 (d,
J = 8.4 Hz, 2 H), 7.64 (d, J = 7.6 Hz, 2 H), 7.48 (t, J = 7.6 Hz, 2 H),
7.41 (t, J = 7.2 Hz, 1 H).
13C NMR (100 MHz, CDCl3): d = 197.8, 145.8, 139.9, 135.8, 128.9,
128.9, 128.2, 127.3, 127.2, 26.7.
4-Methylbiphenyl (11)5
1H NMR (400 MHz, CDCl3): d = 7.58 (t, J = 7.6 Hz, 2 H), 7.49 (d,
J = 8.0 Hz, 2 H), 7.42 (t, J = 7.6 Hz, 2 H), 7.31 (t, J = 7.6 Hz, 1 H),
7.24 (d, J = 8.0 Hz, 2 H), 2.38 (s, 3 H).
13C NMR (100 MHz, CDCl3): d = 141.1, 138.3, 137.0, 129.5, 128.7,
127.3, 127.2, 127.0, 21.1.
4-Fluorobiphenyl (12)7a
1H NMR (400 MHz), CDCl3): d = 7.57–7.53 (m, 4 H), 7.44 (t,
J = 7.6 Hz, 2 H), 7.35 (t, J = 7.2 Hz, 1 H), 7.13 (t, J = 8.8 Hz, 2 H).
13C NMR (100 MHz, CDCl3): d = 163.7, 161.2, 140.2, 137.3, 128.8,
127.2, 115.8, 115.6.
4,4¢-Dimethylbiphenyl (13)5
1H NMR (400 MHz, CDCl3): d = 7.46 (d, J = 8.0 Hz, 4 H), 7.22 (d,
J = 7.6 Hz, 4 H), 2.37 (s, 6 H).
13C NMR (100 MHz, CDCl3): d = 138.3, 136.7, 129.4, 126.8, 21.0.
Synthesis 2005, No. 18, 3039–3044 © Thieme Stuttgart · New York

3044
J.-H. Li et al.
PAPER
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(6) For a paper on imidazolium chloride-palladium catalysts for
the Hiyama cross-coupling reaction, see: Lee, H. M.; Nolan,
S. P. Org. Lett. 2000, 2, 2053.
(7) For recent papers on Pd/DABCO as a catalytic system for
other cross-coupling reactions, see: (a) Li, J.-H.; Liu, W.-J.
Org. Lett. 2004, 6, 2809. (b) Li, J.-H.; Zhang, X.-D.; Xie,
Y.-X. Synthesis 2005, 804. (c) Li, J.-H.; Liang, Y.; Wang,
D.-P.; Liu, W.-J.; Xie, Y.-X.; Yin, D.-L. J. Org. Chem. 2005,
70, 2832.
Synthesis 2005, No. 18, 3039–3044 © Thieme Stuttgart · New York