RuCi3 xH2O-catalyzed direct arylation of arenes with aryl chlorides in the presence of triphenylphosphine

Article abstract of DOI:10.1002/chem.200902612

A study was conducted to demonstrate the RuCl₃·xH ₂O catalytic system for direct arylation of arenes with aryl chlorides. The phenylation of benzo[h]quinoline with chlorobenzene was investigated under preliminary studies. The reaction of benzo[h]quinoline and chlorobenzene N-methyl-2-pyrrolidone (NMP) formed Ph as the only product in 86-93% yields at 120-130 8C in the presence of K₂CO₃ using 5 mol% RuCl₃·xH₂O and 10 mol% PPh₃. It was observed that the presence of an excess of ligand did not affect formation of Ph, while sub-stoichiometric ligand amounts led to a reduced conversion for benzo[h]quinoline. The arylation and benzylation of benzo[h]quinoline with various aryl chlorides was also investigated under the study.

Full text of DOI:10.1002/chem.200902612

COMMUNICATION
DOI: 10.1002/chem.200902612
RuCl3·xH2O-Catalyzed Direct Arylation of Arenes with Aryl Chlorides in
the Presence of Triphenylphosphine
Ning Luo[a] and Zhengkun Yu*[a, b]
Development of a catalytic system utilizing inexpensive
and readily available catalysts and reagents has been a chal-
lenge in organic synthesis. Direct arylation of arenes with or-
lytic system RuCl3·xH2O/PPh3/Na2CO3/N-methyl-2-pyrroli-
done for direct arylation of arenes with aryl chlorides.
In our initial studies, the phenylation of benzo[h]quinoline
(1) with chlorobenzene (2a) was investigated (Scheme 1).
À
ganic coupling reagents through C H bond activation has
recently emerged as a promising alternative to traditional
cross-coupling reactions using organometallic reagents and
coupling partners such as aryl iodides, bromides, triflates,
and other electrophiles[1] due to generation of less toxic
wastes.[2,3] Aryl chlorides are considered as the ideal cou-
pling partners for an economically attractive cross-coupling
process because they are usually cheap and readily avail-
able. However, given that they are much less reactive than
other coupling reagents, their utilization requires the imple-
mentation of specific experimental conditions. To date,
ruthenium still shows the greatest potential for the direct re-
Scheme 1. i) Ru catalyst, ligand, base, solvent.
Using 5 mol% RuCl3·xH2O and 10 mol% PPh3, the reaction
of 1 and 2a in N-methyl-2-pyrrolidone (NMP) formed 3a as
the only product in 86–93% yields at 120–1308C in the pres-
ence of K2CO3; 3a was quantitatively formed when Na2CO3
was used as the base (Table 1, entries 1–5). Thus, Na2CO3
acts more effectively than K2CO3 as a base for this reaction.
Without the PPh3 ligand the reaction did not occur
(entry 6). The presence of an excess of ligand (15–20 mol%)
did not affect formation of 3a, whereas sub-stoichiometric
À
gioselective functionalization of arenes under C H activa-
tion,[4] even though palladium and rhodium have been also
applied for the same purpose.[5] [{RuCl
2ACTHNUTRGNEUNG(p-cymene)}2] and
RuIV complexes were reported to catalyze arylation of
[6–8]
arenes with aryl chlorides in the presence of K2CO3
or
KOAc.[9] RuCl3 is known to mediate the oxidative arylation
of arenes with aryl iodides.[10] RuCl3·xH2O was documented
to promote arylation of arenes with aryl bromides,[11] but it
is inefficient for the same goal with aryl chlorides, although
3
À
it can effect alkylation of activated C
(sp ) H bonds with al-
Table 1. Screening conditions for the reaction of benzo[h]quinoline (1)
and chlorobenzene (2a).[a]
cohols.[12] Herein, we report an economically attractive cata-
Catalyst/
[mol%]
Ligand/ Base
ACHTUNGTRNE[NUNG mol%]
T
t
Conv.[b]
[8C] [h] [%]
U
1
2
3
4
5
6
7
8
9
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/2.5
RuCl3·xH2O/5
PPh3/10 K2CO3
PPh3/10 K2CO3
PPh3/10 Na2CO3 120 24
PPh3/10 Na2CO3 130 18
PPh3/10 Na2CO3 140 16
Na2CO3 140 22
120 24
130 18
86
93
99
>99
100[c]
0
68
32
90
99
[a] N. Luo, Prof. Dr. Z. K. Yu
Dalian Institute of Chemical Physics
Chinese Academy of Sciences
457 Zhongshan Road, Dalian 116023 (P. R. China)
Fax : (+86)411-8437-9227
E-mail: zkyu@dicp.ac.cn
PPh3/5
PPh3/5
Na2CO3 140 24
Na2CO3 140 24
[b] Prof. Dr. Z. K. Yu
PPh3/10 KF
PPh3/10 K3PO4
130 22
130 22
State Key Laboratory of Organometallic Chemistry
Shanghai Institute of Organic Chemistry
Chinese Academy of Sciences
10 RuCl3·xH2O/5
11
12
A
T
99
99
A
U
Na2CO3 130 22
354 Fenglin Road, Shanghai 200032 (P. R. China)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902612.
[a] Conditions: 1 (0.50 mmol), 2a (0.75 mmol), base (1.00 mmol), NMP
(2 mL). [b] Conversion of 1 by GC analysis. [c] Isolated yield, 99%.
Chem. Eur. J. 2010, 16, 787 – 791
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
787

ligand amounts led to a reduced conversion for 1 (entry 7).
KF and K3PO4 can also be used as bases for the reaction
(entries 9 and 10), and both [{RuCl
2ACHTUNGTREN(NUNG p-cymene)}2] and
[RuCl2A(PPh3)3] promoted the arylation but with less efficien-
CHTUNGTRENNUNG
cy than RuCl3·xH2O (entries 11 and 12). Eventually, the re-
action conditions were optimized to: 5 mol% RuCl3·xH2O
as catalyst, 10 mol% PPh3 as ligand, Na2CO3 as base, 1308C
or 1408C in NMP under nitrogen atmosphere.
Next, the arylation and benzylation of 1 with various aryl
chlorides was explored. Under the optimized conditions, the
desired products 3 were obtained in 73–99% (Table 2).
Scheme 3. i) RuCl3·xH2O (15 mol%), PPh3 (30 mol%), Na2CO3 (4.0
equiv), NMP, 1408C, 16 h.
2a (Scheme 4, Table 3). Treatment of 4a with an excess of
2a was expected to form the diarylation product 6a, but the
mono-arylation product 5a was also formed. With 5 mol%
Table 2. Arylation of benzo[h]quinoline (1) with aryl chlorides (2).[a]
3a, 99%
3 f, 75%
3b, 75%
3g, 76%
3c, 80%
3h, 39%
3d, 83%
3i, 87%
3e, 73%[b]
3j, 86%
Scheme 4. i) RuCl3·xH2O (10 mol%), PPh3 (20 mol%), base (4.0 equiv),
NMP (2 mL), 1408C, 22 h.
Table 3. Base effect in the diphenylation of 2-phenylpyridine (4a) with
chlorobenzene (2a).
3k, 73%
3l, 81%
3m, 75%
3n, 0%
3o, 62%[c]
Catalyst/
[mol%]
Base
Yield[a] [%]
[a] Conditions: 1 (0.50 mmol), 2 (0.75 mmol), RuCl3·xH2O (5 mol%), PPh3
(10 mol%), Na2CO3 (1.00 mmol), NMP (2 mL), 1408C, 16 h; isolated yields.
[b] 24 h. [c] RuCl3·xH2O (10 mol%), PPh3 (20 mol%), 24 h.
5a
63
28
6a
1
2
3
4
5
6
7
8
9
10
11[c]
12[d]
13[e]
14
15[f]
RuCl3·xH2O/5
RuCl3·xH2O/5
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
RuCl3·xH2O/10
K2CO3
Na2CO3
K2CO3
Na2CO3
KF
K3PO4
Cs2CO3
NaHCO3
DBU
19
70
50 (40)[b]
47 (35)[b]
0
100 (99)[b]
However, 2’-chloroacetophenone exhibited a low reactivity
to form 3h (39%) presumably due to the steric hindrance of
its 2-substituent, and 4-chloronitrobenzene did not undergo
the reaction. Unexpectedly, with 10 mol% catalyst benzyla-
tion of 1 with benzyl chloride occurred to afford 3o in 62%
yield. Interestingly, polychlorobenzenes underwent direct
polyarylation to give polyarene products. Thus, polyarenes
3p (78%), 3q (81%), and 3r (58%) were obtained from
the reactions of 1 with dichloro-benzenes and 1,3,5-trichlor-
62 (49)[b]
6
38
23
5
9
<1
2
41
95
95
34
56
69
60
34
Et3N
<1
Na2CO3
Na2CO3
Na2CO3
Na2CO3
Na2CO3
25
55
4
2
64
A
R
A
U
obenzene in
a 2:1 and 3:1 molar ratios, respectively
[a] Determined by GC analysis. [b] Isolated yields in parentheses.
[c] PPh3 (10 mol%). [d] In o-xylene. [e] 1308C, 30 h. [f] Without PPh3.
(Schemes 2 and 3). It should be noted that 1,2- dichloroben-
zene exhibited no reactivity.
With 2-phenylpyridine (4a) as the arene substrate, a re-
markable base effect was also observed in its reaction with
RuCl3·xH2O as catalyst, the reaction of 4a and 2a in a 1:3
molar ratio afforded 5a (63%) as the major product by
using K2CO3 base, while 6a was formed in 70% yield in the
presence of Na2CO3 (entries 1 and 2). Using 10 mol% cata-
lyst the reaction proceeded more efficiently: with K2CO3 as
the base 5a and 6a in almost equally amounts, while 4a was
quantitatively transformed to 6a by using Na2CO3 base (en-
tries 3 and 4). Other bases were much less effective than
Na2CO3. It is worth noting that K2CO3 instead of Na2CO3
has usually been used as the base in a cross-coupling reac-
tion,[13] and more attention might be paid to Na2CO3 base to
develop a new catalytic system for cross-couplings.[5j,14] The
methodology was then applied in a variety of reactions of 2-
Scheme 2. i) RuCl3·xH2O (10 mol%), PPh3 (20 mol%), Na2CO3 (3.0
equiv), NMP, 1408C, 16 h.
788
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 787 – 791

À
C H Activation
COMMUNICATION
Table 5. Monoarylation of 2-arylpyridines (4) with aryl chlorides (2).
arylpyridines (4) with aryl chlorides (2), affording the de-
sired products 6 in good to excellent yields (55–99%;
Table 4), among which tridentate terpyridine 6o was ob-
tained in 55% yield. 1-Phenylpyrazole and 2-phenyloxazo-
4
ArCl
Product
Yield[a]
[%]
1
2
5a
5b
68
45
Table 4. Diarylation of 2-arylpyridines (4) with aryl chlorides (2).[a]
4a
3
4
5
4a
4a
4a
5c
5d
5e
58
65
50
6a, 99%
6 f, 82%
6k, 81%
6p, 81%
6b, 60%
6g, 85%
6l, 0%
6c, 74%
6d, 78%
6i, 67%
6n, 58%
6 s, 85%
6e, 56%
6
7
8
4a
4a
4a
5 f
5g
5h
55
55
0
6h, 0%
6j, 95%
6m, 71%
6o, 55%[b]
9
4a
4a
5i
5j
59
58
10
11
4a
4a
5k
45
6q, 70%
6r, 76%
6t, 80%[c]
[a] Conditions: 4 (0.5 mmol) 2 (1.5 mmol) RuCl3·xH2O (10 mol%), PPh3
(20 mol%), Na2CO3 (2.0 mmol), NMP (2 mL), 1408C, 22 h. [b] 36 h.
[c] RuCl3·xH2O (20 mol%), PPh3 (40 mol%), 48 h.
12
13
5o
5p
52
63
2a
2a
line were also directly diarylated, forming 6q–t in 70-85%
yields. In a similar fashion, monoarylation products 5a–k
and 5o,p were synthesized in 45–68% yields (Scheme 5,
14[b]
15[c]
5t
59
75
2a
2a
5u
16[c]
5v
57[d]
[a] Isolated yields. [b] 2a (3.0 equiv), Na2CO3 (4.0 equiv). [c] 2a
(1.5 equiv), Na2CO3 (2.0 equiv). [d] 36 h.
Scheme 5. i) RuCl3·xH2O (10 mol%), PPh3 (20 mol%), base (1.5 equiv),
NMP (2 mL), 1408C, 22 h.
Table 5, entries 1–13) with minor formation of the diaryla-
tion products 6 (8–25%; see the Supporting Information) by
treating 4a with equimolar amount of 2a–k and 2o, respec-
tively. However, reactions of functionalized arenes 4c–e
only formed monoarylation products 5t–v (57–75%; en-
tries 14–16).
Competition reactions were studied to identify the reac-
tivity of substrates. Reaction of 1 and 2a/2j (1:1) in a 1:1
molar ratio reached 93% conversion for 1 in NMP at 1408C
within 16 h to form 3j as the major product, revealing that
4’-chloroacetophenone (2j) is more reactive than 2a
(Scheme 6). Treatment of 1/4a (1:1) with 2a in a 1:1 molar
ratio under similar conditions produced a mixture of 3a, 5a,
and 6a (59:33:8), suggesting that 1 is more reactive than 4a
(see the Supporting Information). From a two-step one-pot
reaction of 4a with 2a and then with 2j (Scheme 7), diaryla-
tion product 6u was obtained in 60% yield with minor for-
mation of 6a and 6j (6a/6j/6u=20:7:73), while the one-pot
reaction of 4a, 2a and 2j only produced a mixture of 5a, 5j,
6a, 6j, and 6u (12:37:6:19:25; see the Supporting Informa-
Chem. Eur. J. 2010, 16, 787 – 791
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
789

Z. K. Yu and N. Luo
RuII species A. Compound 5 is further arylated following
the same mechanism to produce the diarylation product 6.
In conclusion, a simple, efficient and economically attrac-
tive catalytic system has been developed for the direct aryla-
tion of arenes with aryl chlorides by using the catalytic
system
RuCl3·xH2O/PPh3/Na2CO3/NMP.
Here,
using
Scheme 6. i) RuCl3·xH2O (5 mol%), PPh3 (10 mol%), Na2CO3 (2.0
equiv), NMP, 1408C, 16 h; 93% conversion for 1 (3a/3j=43:57).
Na2CO3 as a base instead of K2CO3 was found to result in a
significant enhancement of the efficiency of the system. Our
proposed mechanism suggests that the direct arylation of
arenes is possibly initiated by an in situ generated RuII spe-
cies from RuCl3·xH2O in the presence of PPh3 and Na2CO3
base.
Experimental Section
Scheme 7. i) RuCl3·xH2O (10 mol%), PPh3 (20 mol%), 2a (0.5 mmol)
Na2CO3 (2.0 equiv), NMP, 1408C, 22 h; ii) 2j (0.75 mmol), 1408C, 18 h;
>99% conversion for 4a (6a/6j/6u=20:7:73).
A typical procedure for the arylation of benzo[h]quinoline (1) with aryl
chlorides (2)—phenylation of 1 with chlorobenzene (2a): Under nitrogen
atmosphere, a mixture of RuCl3·xH2O (7 mg, 0.025 mmol), 1 (90 mg,
0.50 mmol), chlorobenzene 2a (85 mg, 0.75 mmol), PPh3 (13 mg,
0.05 mmol), and Na2CO3 (106 mg, 1 mmol) in NMP (2 mL) was stirred at
1408C for 16 h. After cooled to ambient temperature, Et2O (30 mL) and
H2O (20 mL) were added. The organic phase was separated and the
aqueous layer was extracted with Et2O (2ꢁ20 mL). The combined organ-
ic phase was washed with H2O (20 mL) and brine (20 mL), dried over
Na2SO4, and then concentrated under reduced pressure. The resultant
residue was purified by flash silica gel column chromatography (eluent:
petroleum ether (60–908C)/EtOAc=8:1, v/v), affording the target prod-
uct 3a as a white solid (126 mg, 99%). The product was characterized by
1H and 13C{1H} NMR spectroscopy and further confirmed by comparison
with the reported authentic NMR data.
tion), further confirming that 2j is more reactive than 2a.
This protocol thus provides a new route to mixed arylated
arenes.
31P{1H} NMR analysis of the reaction mixture of 1 and 2a
under the reaction conditions or a mixture of RuCl3·xH2O,
Ph3P and Na2CO3 in NMP heated at 1408C for two hours re-
vealed formation of Ph3PO and presence of free Ph3P in the
mixtures, suggesting that reduction of RuCl3·xH2O occurred
during the reaction. Thus, a reaction mechanism is proposed
in Scheme 8. RuCl3·xH2O is presumably reduced to RuII
Acknowledgements
We are grateful to the National Basic Research Program of China
(2009CB825300), the National Natural Science Foundation of China
(20772124, 20972157), and the Knowledge Innovation Program of the
Chinese Academy of Sciences (DICP K2009D04) for support of this re-
search.
À
C H
Keywords: arenes
activation · ruthenium
·
aryl chlorides
·
arylation
·
[1] Transition Metals for Organic Synthesis, 2nd ed. (Eds.: M. Beller, C.
Bolm), Wiley-VCH, Weinheim, 2004.
Scheme 8. Proposed mechanism.
[2] Selected recent reviews on direct arylation, see: a) G. P. McGlacken,
L. M. Bateman, Chem. Soc. Rev. 2009, 38, 2447; b) J. C. Lewis, R. G.
Bergman, J. A. Ellman, Acc. Chem. Res. 2008, 41, 1013; c) I. V. Sere-
gin, V. Gevorgyan, Chem. Soc. Rev. 2007, 36, 1173; d) D. Alberico,
M. E. Scott, M. Lautens, Chem. Rev. 2007, 107, 174; e) L. Acker-
mann, Top. Organomet. Chem. 2008, 24, 35; f) T. Satoh, M. Miura,
Top. Organomet. Chem. 2008, 24, 61; g) L. Ackermann, Synlett 2007,
507; h) J.-Q. Yu, R. Giri, X. Chen, Org. Biomol. Chem. 2006, 4,
4041; i) O. Daugulis, V. G. Zaitsev, D. Shabashov, Q. N. Pham, A.
Lazareva, Synlett 2006, 3382; j) V. Ritleng, C. Sirlin, M. Pfeffer,
Chem. Rev. 2002, 102, 1731.
species A in situ with PPh3 and a base by heating. It has
been known that in refluxing methanol RuCl3·xH2O can be
reduced to RuII complexes in the presence of PPh3.[15] Oxi-
dative addition of aryl chloride to A leads to RuIV inter-
2
À
mediate B, thus activating the C
(sp ) Cl bond. B reacts with
arene 1 or 4 in the presence of Na2CO3 base to form RuIV
[3] Selected recent reports on cross-couplings of two arenes, see:
a) S. H. Cho, S. J. Hwang, S. Chang, J. Am. Chem. Soc. 2008, 130,
9254; b) T. Dohi, M. Ito, K. Morimoto, M. Iwata, Y. Kita, Angew.
Chem. 2008, 120, 1321; Angew. Chem. Int. Ed. 2008, 47, 1301; c) B.-
À
species C through arene C H bond activation. Reductive
elimination by coordination of a ligand to C affords the de-
sired product 3 or 5 and regenerates the catalytically active
790
www.chemeurj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2010, 16, 787 – 791

À
C H Activation
COMMUNICATION
J. Li, S.-L. Tian, Z. Fang, Z.-J. Shi, Angew. Chem. 2008, 120, 1131;
E. Villemure, H.-Y. Sun, S. Lasserre, N. Guimond, M. Lecavallier,
K. Fagnou, J. Am. Chem. Soc. 2009, 131, 3291; f) L. Ackermann, A.
Althammer, S. Fenner, Angew. Chem. 2009, 121, 207; Angew. Chem.
Int. Ed. 2009, 48, 201; g) Z.-H. Guan, Z.-H. Ren, S. M. Spinella, S.
Yu, Y.-M. Liang, X.-M. Zhang, J. Am. Chem. Soc. 2009, 131, 729;
h) J. Canivet, J. Yamaguchi, I. Ban, K. Itami, Org. Lett. 2009, 11,
1733; i) A. M. Berman, J. C. Lewis, R. G. Bergman, J. A. Ellman, J.
Am. Chem. Soc. 2008, 130, 14926; j) X. D. Zhao, Z. K. Yu, J. Am.
Chem. Soc. 2008, 130, 8136.
Angew. Chem. Int. Ed. 2008, 47, 1115; d) D. R. Stuart, K. Fagnou,
Science 2007, 316, 1172; e) D. R. Stuart, E. Villemure, K. Fagnou, J.
Am. Chem. Soc. 2007, 129, 12072; f) K. L. Hull, M. S. Sanford, J.
Am. Chem. Soc. 2007, 129, 11904; g) Y.-Z. Li, B.-J. Li, X.-Y. Lu, S.
Lin, Z.-J. Shi, Angew. Chem. 2009, 121, 3875; Angew. Chem. Int. Ed.
2009, 48, 3817; h) Y.-X. Jia, E. P. Kꢂndig, Angew. Chem. 2009, 121,
1664; Angew. Chem. Int. Ed. 2009, 48, 1636; i) G. Deng, L. Zhao, C.-
J. Li, Angew. Chem. 2008, 120, 6374; Angew. Chem. Int. Ed. 2008,
47, 6278.
[6] a) L. Ackermann, A. Althammer, R. Born, Angew. Chem. 2006, 118,
2681; Angew. Chem. Int. Ed. 2006, 45, 2619; b) L. Ackermann, Org.
Lett. 2005, 7, 3123.
[7] L. Ackermann, R. Vicente, A. Althammer, Org. Lett. 2008, 10, 2299.
[8] L. Ackermann, R. Born, P. ꢅlvarez-Bercedo, Angew. Chem. 2007,
119, 6482; Angew. Chem. Int. Ed. 2007, 46, 6364.
[4] Selected recent leading reports on Ru-catalyzed direct arylation of
arenes, see: a) R. Martinez, M.-O. Simon, R. Chevalier, C. Pautigny,
J.-P. Genet, S. Darses, J. Am. Chem. Soc. 2009, 131, 7887; b) T.
Kochi, S. Urano, H. Seki, E. Mizushima, M. Sato, F. Kakiuchi, J.
Am. Chem. Soc. 2009, 131, 2792; c) I. ꢃzdemir, S. Demir, B. Cetin-
kaya, C. Gourlaouen, F. Maseras, C. Bruneau, P. H. Dixneuf, J. Am.
Chem. Soc. 2008, 130, 1156; d) L. Ackermann, M. Mulzer, Org. Lett.
2008, 10, 5043; e) S. J. Pastine, D. V. Gribkov, D. Sames, J. Am.
Chem. Soc. 2006, 128, 14220; f) S. Oi, E. Aizawa, Y. Ogino, Y.
Inoue, J. Org. Chem. 2005, 70, 3113.
[5] Selected recent reports on palladium and rhodium-catalyzed direct
arylation of arenes, see: a) M. Miyasaka, A. Fukushima, T. Satoh, K.
Hirano, M. Miura, Chem. Eur. J. 2009, 15, 3674; b) Y.-H. Zhang, B.-
F. Shi, J.-Q. Yu, J. Am. Chem. Soc. 2009, 131, 5072; c) C. Wang, I.
Piel, F. Glorius, J. Am. Chem. Soc. 2009, 131, 4194; d) X. D. Zhao,
ˇ
[9] F. Pozgan, P. H. Dixneuf, Adv. Synth. Catal. 2009, 351, 1737.
[10] K. Cheng, Y. H. Zhang, J. L. Zhao, C. S. Xie, Synlett 2008, 9, 1325.
[11] L. Ackermann, A. Althammer, R. Born, Tetrahedron 2008, 64, 6115.
[12] T. Jensen, R. Madsen, J. Org. Chem. 2009, 74, 3990.
[13] L. Ackermann, P. Novꢆk, R. Vicente, N. Hofmann, Angew. Chem.
2009, 121, 6161; Angew. Chem. Int. Ed. 2009, 48, 6045.
[14] W. W. Jin, Z. K. Yu, W. He, W. J. Ye, W.-J. Xiao, Org. Lett. 2009, 11,
1317.
[15] T. A. Stephenson, G. Wilkinson, J. Inorg. Nucl. Chem. 1966, 28, 945.
´
E. Dimitrijevic, V. M. Dong, J. Am. Chem. Soc. 2009, 131, 3466;
Received: September 23, 2009
e) L.-C. Campeau, D. R. Stuart, J.-P. Leclerc, M. Bertrand-Laperlꢄ,
Published online: December 8, 2009
Chem. Eur. J. 2010, 16, 787 – 791
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
791