Palladium-mediated olefination of 2-(tert-butyldimethylsilyl)pyridine by sp3 C-H activation

Article abstract of DOI:10.1055/s-0030-1260075

An unprecedented direct alkenylation of 2-(tert-butyl-dimethylsilyl) pyridine with acrylates through palladium-mediated C-H activation on a nonacidic sp³ carbon is reported. This method provides an efficient approach to allylsilanes. Georg Thie

Full text of DOI:10.1055/s-0030-1260075

2590
SPECIAL TOPIC
Palladium-Mediated Olefination of 2-(tert-Butyldimethylsilyl)pyridine by sp3
C–H Activation
O
lefination of 2-(
o
tert-Butyldi
n
gyridine Wang, Haibo Ge*
Department of Chemistry and Chemical Biology, Indiana University Purdue University Indianapolis, Indianapolis, IN 46202-3274, USA
Fax +1(317)2744701; E-mail: geh@iupui.edu
Received 9 April 2011
methylsilyl)pyridine (4) and we obtained the desired
Abstract: An unprecedented direct alkenylation of 2-(tert-butyl-
product 5a, albeit in poor yield, when tetrahydrofuran, tol-
dimethylsilyl)pyridine with acrylates through palladium-mediated
C-H activation on a nonacidic sp3 carbon is reported. This method
provides an efficient approach to allylsilanes.
uene, or 1,2-dichloroethane was used as the solvent
(Table 1, entries 1–3). We noted that a source of palladi-
um(II) is required for this coupling reaction (entry 4). Fur-
ther screening of various palladium(II) sources, oxidants,
bases, reaction temperatures, and times (entries 5–19) un-
fortunately resulted in no improvement in the coupling
yield. Therefore, the coupling reaction was carried out
with a stoichiometric amount of benzonitrile(dichlo-
ro)palladium(II) [Pd(PhCN)2Cl2] in the absence of cop-
per(II) acetate. Surprisingly, the yield was only slightly
improved (entry 20). Presumably, the product acts as a bi-
dentate ligand to coordinate palladium(II), and thus con-
sumes this metal species. To solve this problem, we used
an oxidant to oxidize the palladium(0) generated in the re-
action system back to palladium(II), and we obtained a
reasonable yield (entry 21). Further studies showed that
optimal results were obtained with a stoichiometric
amount of palladium(II) chloride in the presence of an ex-
cess of copper(II) actetate (entry 23).
Key words: palladium, olefination, pyridine
Transition metal-catalyzed cross coupling reactions to
form carbon–carbon or carbon–heteroatom bonds are
among the most important reactions for the construction
of organic molecules.1 Among these, direct cross coupling
of (hetero)arenes through palladium-catalyzed C–H func-
tionalization,2 has received considerable attention over
the past decade, and significant achievements has been
made in recent years.3 In comparison, palladium-cata-
lyzed or palladium-mediated C–H activation of nonacidic
sp3 carbons is still a challenge because of the strength of
the C–H bond. Some recent progress has been made in
this area.4 However, most of the processes developed ap-
ply only to benzylic C–H bonds or to substrates with a
tert-butyl fragment. In our continuing efforts to develop
oxidative cross coupling reactions on novel substrates, we
report a direct alkenylation of 2-(tert-butyldimethylsi-
lyl)pyridine with acrylates by palladium-mediated C–H
activation of an sp3 carbon.
Next, by using the optimized reaction conditions de-
scribed above, we examined the scope for the selection of
the alkene (Table 2). As expected, monosubstituted termi-
nal acrylates 2a–e gave the corresponding products 5a–e
in good yields (52–82%; entries 1–5). The sterically hin-
dered acrylate 2f was also compatible, although the prod-
uct 5f was obtained in a low yield (entry 6). Furthermore,
terminal alkene products (5g and 5h) were isolated in
good yield from the coupling of 4 with alkenes 2g and 2h
in 75 and 73% yield, respectively (entries 7 and 8); this is
presumably the result of a steric effect during the b-hy-
dride elimination step in the Heck cycle.
This work was triggered by an earlier report on the cyclo-
palladation of 2-(trimethylsilyl)pyridine (1) with palladi-
um(II) acetate in benzene under mild conditions.5 Our
investigation therefore began with attempts to couple 2-
(trimethylsilyl)pyridine (1) with tert-butyl acrylate (2a) in
the presence of 10 mol% of palladium(II) acetate or chlo-
ride and two equivalents of copper(II) acetate as an oxi-
dant (Scheme 1). Decomposition of the pyridine 1
occurred during the reaction and none of the desired prod-
uct 3 was obtained. Faced with this problem, we decided
to replace the substrate with more-stable 2-(tert-butyldi-
In conclusion, we have developed a novel procedure for
the direct alkenylation of 2-(tert-butyldimethylsilyl)pyri-
dine (4) with acrylates 2 by palladium-mediated sp3 C–H
activation. Because the pyridylsilyl group is potentially
PdX2 (10 mol%)
Cu(OAc)2 (2.0 equiv)
OtBu
OtBu
Me
Me
+
N
Si
N
Si
base (2.0 equiv)
solvent
O
Me
Me
Me
O
1
2a
3
Scheme 1
SYNTHESIS 2011, No. 16, pp 2590–2594
x
x.
x
x
.
2
0
1
1
Advanced online publication: 17.06.2011
DOI: 10.1055/s-0030-1260075; Art ID: C01311SS
© Georg Thieme Verlag Stuttgart · New York

SPECIAL TOPIC
Olefination of 2-(tert-Butyldimethylsilyl)pyridine
2591
Table 1 Optimization of the Reaction Conditions
Me
Si
OtBu
PdX2, oxidant
OtBu
Me
Me
N
Si
+
N
base, 100–150 °C
O
O
4
2a
5a
Entrya
1
PdX2 (mol%)
Oxidant (2 equiv)
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
AgOAc
Solvent
THF
toluene
DCE
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
THF
Base
Temp (°C)
100
100
100
100
100
100
100
100
100
100
100
100
100
100
100
120
150
120
100
100
100
100
100
Time (h) Yieldb (%)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
–
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K2HPO4
K2CO3
AgOAc
Na2CO3
t-BuONa
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
12
24
48
12
12
12
12
19
15
18
–
2
3
4
5
Pd(OAc)2 (10)
9
6
Pd (CH3CN)2Cl2 (10)
PdBr2 (10)
13
10
13
11
14
16
14
14
11
14
21
22
19
21
30
65
66
70c
7
8
Na2PdCl4 (10)
9
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (10)
Pd(PhCN)2Cl2 (100)
Pd(MeCN)2Cl2 (100)
Pd(OAc)2 (100)
PdCl2 (100)
10
11
12
13
14
15
16
17
18
19
20
21
22
23
Ce(SO4)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
–
Cu(OAc)2
Cu(OAc)2
Cu(OAc)2
a Conditions: 4 (0.2 mmol), 2a (0.4 mmol), PdX2 (0.02 or 0.2 mmol), oxidant (0.4 mmol), base (0.4 mmol, 2 equiv), solvent (2 mL), 100–150 °C,
12–48 h.
b Yields are based on 4 and were determined by 1H NMR of the crude product using CH2Br2 as the internal standard.
c Isolated yield 64%.
removable or convertible,6 this method should find a
Inc.) were used. Flash silica gel (32–63 mm; Dynamic Adsorbents
Inc.) was used for air-flashed column chromatography. The 1H and
broad range of applications in the preparation of syntheti-
13C NMR spectra were recorded on a Bruker 500 MHz Fourier-
transform NMR spectrometer.
cally useful allylsilyl intermediates. Further studies on a
catalytic version of this transformation are currently in
progress in our laboratory.
2-(tert-Butyldimethylsilyl)pyridine (4)
A 2.5 M soln of BuLi in hexanes (20 mL, 50 mmol) was slowly add-
ed over 30 min to a stirred soln of 2-bromopyridine (7.9 g, 50 mmol)
All reactions were carried out in oven-dried glassware. The palladi-
in anhyd THF (100 mL) at –78 °C, and the resulting mixture was
um(II) compounds, oxidants, bases, and solvents were purchased
stirred at the –78 °C for 30 min. A soln t-BuSi(Cl)Me2 (7.5 g, 50
from Acros or Sigma-Aldrich and used directly. For TLC analysis,
mmol) in THF (20 mL) was then added dropwise at –78 °C, and the
precoated plates (w/h F254, 0.25-mm thick; Dynamic Adsorbents
mixture was allowed to warm to r.t. and stirred overnight. The reac-
Synthesis 2011, No. 16, 2590–2594 © Thieme Stuttgart · New York

2592
C. Wang, H. Ge
SPECIAL TOPIC
Table 2 Scope of Alkenes in the C–H Functionalization
PdCl2 (1.0 equiv)
R3
Cu(OAc)2 (2.0 equiv)
Me
Me
Me
Si
Me
Si
OR1
OR1
R2
OR1
N
Si
+
N
or
N
K3PO4 (2.0 equiv)
THF, 100 °C, 12 h
R2
O
O
O
4
2
5a–f
5g,h
Entrya
1
Substrate 2
Product 5
Yield (%)b
64
Me
Si
OtBu
O
OtBu
OMe
2a
5a
N
N
O
Me
Si
OMe
O
2
3
4
5
6
7
8
2b
2c
2d
2e
2f
5b
5c
5d
5e
5f
52
62
65
82
39
75
73
O
O
O
O
Me
Si
OEt
O
OEt
N
N
N
N
N
N
Me
Si
OnBu
O
OnBu
OBn
OMe
OMe
OtBu
Me
Si
OBn
O
Me
Si
OMe
O
O
O
O
Me
Si
OMe
O
2g
2h
5g
5h
Me
Si
OtBu
O
a Reaction conditions: 4 (0.2 mmol), 2a–h (0.4 mmol), PdCl2 (0.2 mmol), Cu(OAc)2 (0.4 mmol), K3PO4 (0.4 mmol), THF (4 mL), 100 °C, 12 h.
b Isolated yields based on 4.
tion was quenched by slow addition of brine (100 mL) at 0 °C. The
organic phase was then separated and the aqueous phase was ex-
tracted with Et2O (2 × 100 mL). The combined organic phase was
dried (Na2SO4) and concentrated under vacuum to give the crude
product as a dark oil. This was purified by flash chromatography
(hexanes–EtOAc, 30:1) and further purified by distillation under re-
duced pressure to give a colorless liquid; yield: 5.2 g (54%).
1H NMR (500 MHz, CDCl3): d = 8.78 (d, 1 H, J = 4.5), 7.57 (td, 1
H, J = 7.5, 1.5 Hz), 7.49 (d, 1 H, J = 7.5 Hz), 7.20–7.15 (m, 1 H),
0.92 (s, 9 H), 0.32 (s, 6 H).
Alkyl tert-Butyl (2E)-4-[tert-butyl(methyl)pyridin-2-ylsilyl]but-
2-enoates and Alkyl 2-{2-[tert-butyl(methyl)pyridin-2-ylsi-
lyl]ethyl}acrylates (5); General Procedure
An oven-dried pressure tube was charged with silylpyridine 4 (0.2
mmol), acrylate 2 (0.4 mmol), PdCl2 (0.2 mmol), Cu(OAc)2 (0.4
mmol), K3PO4 (0.4 mmol), and THF (4 mL). The tube was sealed,
stirred at 100 °C for 12 h, and then cooled to r.t. The mixture was
diluted with EtOAc, filtered through a pad of Celite, and concentrat-
ed under vacuum. The residue was purified by flash chromatogra-
phy (hexanes–EtOAc, 30:1)
Synthesis 2011, No. 16, 2590–2594 © Thieme Stuttgart · New York

SPECIAL TOPIC
Olefination of 2-(tert-Butyldimethylsilyl)pyridine
2593
tert-Butyl (2E)-4-[tert-Butyl(methyl)pyridin-2-ylsilyl]but-2-
enoate (5a)
2.20 (m, 2 H), 1.25–1.13 (m, 1 H), 1.05–1.00 (m, 1 H), 0.93 (s, 9 H),
0.37 (s, 3 H).
13C NMR (125 MHz, CDCl3): d = 167.8, 165.0, 150.1, 143.1, 133.7,
130.3, 123.5, 122.6, 51.3, 26.7, 26.4, 17.2, 9.3, –8.6.
1H NMR (500 MHz, CDCl3): d = 8.77 (td, J = 4.5, 1.5 Hz, 1 H),
7.57 (td, J = 7.5, 2.0 Hz, 1 H),7.45 (d, J = 7.5 Hz, 1 H), 7.22–7.15
(m, 1 H), 6.95–6.88 (m, 1 H), 5.60 (d, J = 14.5 Hz, 1 H), 2.28–2.20
(m, 1 H), 2.05–1.95 (m, 1 H), 1.42 (s, 9 H), 0.94 (s, 9 H), 0.34 (s, 3
H).
tert-Butyl 2-{2-[tert-Butyl(methyl)pyridin-2-ylsilyl]ethyl}acry-
late (5h)
13C NMR (125 MHz, CDCl3): d = 166.2, 164.1, 150.0, 146.3, 133.7,
130.3, 122.9, 121.5, 79.5, 28.2, 26.7, 18.3, 17.5, –8.6.
1H NMR (500 MHz, CDCl3): d = 8.78 (d, J = 5.0 Hz, 1 H), 7.60–
7.55 (m, 1 H), 7.50–7.45 (m, 1 H), 7.23–7.15 (m, 1 H), 6.00 (d,
J = 1.5 Hz, 1 H), 5.46 (d, J = 1.5 Hz, 1 H), 2.43–2.13 (m, 2 H), 1.48
(s, 9 H), 1.22–1.15 (m, 1 H), 1.05–0.95 (m, 1 H), 0.93 (s, 9 H), 0.36
(s, 3 H).
Methyl(2E)-4-[tert-Butyl(methyl)pyridin-2-ylsilyl]but-2-enoate
(5b)
1H NMR (500 MHz, CDCl3): d = 8.78 (d, J = 4.5 Hz, 1 H), 7.58 (t,
J = 7.0 Hz, 1 H), 7.45 (d, J = 7.0 Hz, 1 H), 7.25–7.19 (m, 1 H),
7.10–7.00 (m, 1 H), 5.69 (d, J = 15.5 Hz, 1 H), 3.65 (s, 3 H), 2.34–
2.20 (m, 1 H), 2.10–2.03 (m, 1 H), 0.94 (s, 9 H), 0.34 (s, 3 H).
13C NMR (125 MHz, CDCl3): d =166.7, 165.5, 150.0, 144.8, 133.5,
130.2, 122.8, 122.3, 80.3, 28.1, 26.8, 17.2, 12.2, 9.4, –8.6.
13C NMR (125 MHz, CDCl3): d = 167.1, 163.9, 150.1, 148.1, 133.7,
130.4, 123.0, 119.3, 51.2, 26.7, 18.7, 17.6, –8.6.
Acknowledgment
We gratefully acknowledge the financial support provided by
Indiana University Purdue University Indianapolis. The Bruker 500
MHz NMR was purchased using funds from an NSF-MRI award
(CHE-0619254).
Ethyl (2E)-4-[tert-Butyl(methyl)pyridin-2-ylsilyl]but-2-enoate
(5c)
1H NMR (500 MHz, CDCl3): d = 8.78 (d, J = 5.0 Hz, 1 H), 7.58 (td,
J = 7.5, 1.5 Hz, 1 H), 7.46 (d, J = 7.5 Hz, 1 H), 7.23–7.19 (m, 1 H),
7.07–6.95 (m, 1 H), 5.67 (d, J = 15.0 Hz, 1 H), 4.11 (q, J = 7.0 Hz,
2 H), 2.32–2.27 (m, 1 H), 2.08–2.03 (m, 1 H), 1.23 (t, J = 7.0 Hz, 3
H), 0.94 (s, 9 H), 0.34 (s, 3 H).
References
(1) For some recent reviews, see: (a) Luh, T. Y.; Leung, M. K.;
Wong, K. T. Chem. Rev. 2000, 100, 3187. (b) Lyons, T. W.;
Sanford, M. S. Chem. Rev. 2000, 100, 1147. (c) Dounay, A.
B.; Overman, L. E. Chem. Rev. 2003, 103, 2945.
13C NMR (125 MHz, CDCl3): d = 166.7, 164.0, 150.1, 147.7, 133.7,
130.4, 123.0, 119.7, 59.8, 26.7, 18.6, 17.5, 14.3, –8.6.
(d) Fagnou, K.; Lautens, M. Chem. Rev. 2003, 103, 169.
(e) Culkin, D. A.; Hartwig, J. F. Acc. Chem. Res. 2003, 36,
234. (f) Nicolaou, K. C.; Bulger, P. G.; Sarlah, D. Angew.
Chem. Int. Ed. 2005, 44, 4442. (g) Christmann, U.; Vilar, R.
Angew. Chem. Int. Ed. 2005, 44, 366. (h) Frisch, A. C.;
Beller, M. Angew. Chem. Int. Ed. 2005, 44, 674. (i)Godula,
K.; Sames, D. Science (Washington, D. C.) 2006, 312, 67.
(j) Alberico, D.; Scott, M. E.; Lautens, M. Chem. Rev. 2007,
107, 174. (k) Yin, L. X.; Liebscher, J. Chem. Rev. 2007, 107,
133. (l) Catellani, M.; Motti, E.; Della Ca’, N. Acc. Chem.
Res. 2008, 41, 1512. (m) Fu, G. C. Acc. Chem. Res. 2008,
41, 1555. (n) Martin, R.; Buchwald, S. L. Acc. Chem. Res.
2008, 41, 1461. (o) Thansandote, P.; Lautens, M. Chem.
Eur. J. 2009, 15, 5874. (p) Zhang, M. Adv. Synth. Catal.
2009, 351, 2245.
Butyl (2E)-4-[tert-Butyl(methyl)pyridin-2-ylsilyl]but-2-enoate
(5d)
1H NMR (500 MHz, CDCl3): d = 8.78 (d, J = 4.5 Hz, 1 H), 7.57 (t,
J = 7.5 Hz, 1 H), 7.45 (d, J = 7.5 Hz, 1 H), 7.23–7.18 (m, 1 H),
7.07–6.95 (m, 1 H), 5.67 (d, J = 15.5 Hz, 1 H), 4.05 (t, J = 6.5 Hz,
2 H), 2.33–2.27 (m, 1 H), 2.08–2.03 (m, 1 H), 1.60–1.58 (m, 2 H),
1.34–1.31 (m, 2 H), 0.94 (s, 9 H), 0.91 (t, J = 7.5 Hz, 3 H), 0.34 (s,
3 H).
13C NMR (125 MHz, CDCl3): d = 166.8, 164.0, 150.0, 147.6, 133.7,
130.4, 123.0, 119.7, 63.8, 30.7, 26.7, 19.2, 18.7, 17.6, 13.7, –8.6.
Benzyl (2E)-4-[tert-Butyl(methyl)pyridin-2-ylsilyl]but-2-enoate
(5e)
1H NMR (500 MHz, CDCl3): d = 8.78 (d, J = 4.5 Hz, 1 H), 7.57 (td,
J = 7.5, 2.0 Hz, 1 H), 7.50 (t, J = 7.5 Hz, 1 H), 7.40–7.30 (m, 5 H),
7.25–7.20 (m, 1 H), 7.15–7.05 (m, 1 H), 5.73 (d, J = 15.5 Hz, 1 H),
5.11 (s, 2 H), 2.35–2.28 (m, 1 H), 2.08–2.03 (m, 1 H), 0.94 (s, 9 H),
0.34 (s, 3 H).
(2) For some recent reviews, see: (a) Jia, C.; Kitamura, T.;
Fujiwara, Y. Acc. Chem. Res. 2001, 34, 633. (b) Fabrizi, G.
Chem. Rev. 2005, 105, 2873. (c) Beccalli, E. M.; Broggini,
G.; Martinelli, M.; Sottocornola, S. Chem. Rev. 2007, 107,
5318. (d) Chen, X.; Engle, K. M.; Wang, D. H.; Yu, J. Q.
Angew. Chem. Int. Ed. 2009, 48, 509.
13C NMR (125 MHz, CDCl3): d = 166.5, 163.9, 150.1, 148.6, 141.8,
136.4, 133.7, 130.4, 128.5, 128.0, 123.0, 119.3, 65.7, 26.7, 18.8,
17.6, –8.5.
(3) For some recent examples of palladium-catalyzed C–H
functionalization reaction, see: (a) Jia, C.-G.; Piao, D.-G.;
Oyamada, J. Z.; Lu, W. J.; Kitamura, T.; Fujiwara, Y.
Science (Washington, D. C.) 2000, 287, 1992. (b) Ferreira,
E. M.; Stoltz, B. M. J. Am. Chem. Soc. 2003, 125, 9578.
(c) Zhang, H.; Ferreira, E. M.; Stoltz, B. M. Angew. Chem.
Int. Ed. 2004, 43, 6144. (d) Grimster, N. P.; Gauntlett, C.;
Godfrey, C. R. A.; Gaunt, M. J. Angew. Chem. Int. Ed. 2005,
44, 3125. (e) Beck, E. M.; Grimster, N. P.; Hatley, R.;
Gaunt, M. J. J. Am. Chem. Soc. 2006, 128, 2528. (f) Stuart,
D. R.; Fagnou, K. Science (Washington, D. C.) 2007, 316,
1172. (g) Yang, S.-D.; Sun, C.-L.; Fang, Z.; Li, B.-J.; Li,
Y.-Z.; Shi, Z.-J. Angew. Chem. Int. Ed. 2008, 47, 1473.
(h) Ge, H.-B.; Niphakis, M. J.; Georg, G. I. J. Am. Chem.
Soc. 2008, 130, 3708. (i) Würtz, S.; Rakshit, S.; Neumann,
J. J.; Dröge, T.; Glorius, F. Angew. Chem. Int. Ed. 2008, 47,
7230. (j) Wang, C.; Piel, I.; Glorius, F. J. Am. Chem. Soc.
Methyl (2E)-4-[tert-Butyl(methyl)pyridin-2-ylsilyl]-3-methyl-
but-2-enoate (5f)
1H NMR (500 MHz, CDCl3): d = 8.79 (d, J = 1.0 Hz, 1 H), 7.57 (t,
J = 7.5 Hz, 1 H), 7.50 (d, J = 7.5 Hz, 1 H), 7.22–7.18 (m, 2 H), 5.50
(s, 1 H), 3.61 (s, 3 H), 2.42 (d, J = 12.0 Hz, 1 H), 2.05–1.95 (m, 4
H), 0.94 (s, 9 H), 0.35 (s, 3 H).
13C NMR (125 MHz, CDCl3): d = 167.2, 164.3, 160.9, 150.0, 133.7,
130.4, 123.0, 113.5, 50.5, 26.7, 26.4, 21.4, 17.6, –8.5.
Methyl 2-{2-[tert-Butyl(methyl)pyridin-2-ylsilyl]ethyl}acrylate
(5g)
1H NMR (500 MHz, CDCl3): d = 8.78 (d, J = 5.0 Hz, 1 H), 7.57 (td,
J = 7.5, 1.5 Hz, 1 H), 7.50 (d, J = 7.5, 1 H), 7.20–7.15 (m, 1 H), 6.09
(d, J = 1.0 Hz, 1 H), 5.56 (d, J = 1.0 Hz, 1 H), 3.73 (s, 3 H), 2.30–
Synthesis 2011, No. 16, 2590–2594 © Thieme Stuttgart · New York

2594
C. Wang, H. Ge
SPECIAL TOPIC
2009, 131, 4194. (k) Zhang, Y.-H.; Shi, B.-F.; Yu, J.-Q.
J. Am. Chem. Soc. 2009, 131, 5072. (l) Goikhman, R.;
Jacques, T. L.; Sames, D. J. Am. Chem. Soc. 2009, 131,
3042. (m) Li, M.-Z.; Ge, H.-B. Org. Lett. 2010, 12, 3464.
(n) Fang, P.; Li, M.-Z.; Ge, H.-B. J. Am. Chem. Soc. 2010,
132, 11898. (o) Li, M.-Z.; Li, ; L, X.; Ge, H.-B. Adv. Synth.
Catal. 2010, 352, 2445.
(4) For a recent review, see: Jazzar, R.; Hitce, J.; Renaudat, A.;
Sofack-Kreutzer, J.; Baudoin, O. Chem. Eur. J. 2010, 16,
2654.
(5) Fuchita, Y.; Nakashima, M.; Hiraki, K.; Kawatani, M.
J. Chem. Soc., Dalton Trans. 1988, 785.
(6) (a) Langkopf, E.; Schinzer, D. Chem. Rev. 1995, 95, 1375.
(b) Kamei, T.; Fujita, K.; Itami, K.; Yoshida, J.-i. Org. Lett.
2005, 7, 4725. (c) Frisch, A. C.; Beller, M. Angew. Chem.
Int. Ed. 2008, 47, 1560.
Synthesis 2011, No. 16, 2590–2594 © Thieme Stuttgart · New York