Formation of cine-substitution products in the Suzuki-Miyaura cross-coupling reaction catalyzed by dinuclear palladium complexes

Article abstract of DOI:10.1002/hlca.201200454

The Suzuki-Miyaura coupling reaction catalyzed by dinuclear palladium complexes gave cine-substitution products along with ordinary ipso-substitution products. In the reaction in (D₆)benzene, the ipso position of the cine-substitution product was highly deuterated. The H/D exchange also occurred in various positions of benzene rings. Copyright

Full text of DOI:10.1002/hlca.201200454

Helvetica Chimica Acta – Vol. 96 (2013)
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Formation of cine-Substitution Products in the SuzukiꢀMiyaura Cross-
Coupling Reaction Catalyzed by Dinuclear Palladium Complexes
by Naofumi Tsukada*1), Tsubasa Abe, and Yoshio Inoue
Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan
(phone/fax: þ 81-54-238-4759; e-mail: sntsuka@ipc.shizuoka.ac.jp)
The SuzukiꢀMiyaura coupling reaction catalyzed by dinuclear palladium complexes gave cine-
substitution products along with ordinary ipso-substitution products. In the reaction in (D6)benzene, the
ipso position of the cine-substitution product was highly deuterated. The H/D exchange also occurred in
various positions of benzene rings.
Introduction. – Most organic reactions catalyzed by transition metal complexes take
place on a single metal center. If there are more than two metal centers in one
molecule, cooperation of the metal centers variegates their catalytic ability [1].
Improvement of the efficiency and selectivity, promotion of reactions that are difficult
using a mononuclear complex, and formation of unexpected products can be possible.
We previously designed a new chelate-bridging ligand, N,N’-bis[2-(diphenylphosphi-
no)phenyl]formamidinato (dpfam), for the synthesis of dinuclear Pd complexes, in
which two Pd centers are tied in close proximity with or without a metalꢀmetal bond
[2]. The dinuclear Pd complexes served as effective catalysts for several valuable
transformations of organic compounds [3][4]. For example, dinuclear complex 1a
catalyzed addition reactions of various compounds to alkynes via CꢀH activation [3].
In the course of our study for the applicability of 1, we found that cine-substitution
products were formed along with ordinary ipso-substitution products when the
SuzukiꢀMiyaura coupling reaction was conducted in the presence of 1.
Although various types of nucleophilic cine-substitution reactions have been
reported, cine-substitution in transition metal-catalyzed cross-coupling reaction seems
to be rather rare [5]. There are several reports on cine-substitution on alkenylstannanes
in Stille coupling [6]. A similar reaction takes place on alkenylsilanes in Hiyama
coupling [7]. In Negishi and Heck couplings, cine-substitution on alkenyl halides and
pseudo-halides (phosphates and tosylates) are observed [8][9]. Some Rh-catalyzed
reactions, in which cine-substitution occurs on alkenyl acetates or sulfones, were also
reported [10]. While there are several examples for various alkenyl compounds, cine-
substitution on aryl compounds in cross-couplings is rare [11]2). Herein, we report cine-
substitution on aryl bromides in SuzukiꢀMiyaura coupling reaction catalyzed by
dinuclear Pd complexes 1.
1
)
)
Present address: Department of Chemistry, Faculty of Science, Shizuoka University, Shizuoka 422-
8529, Japan.
For examples of formal cine-substitution reactions, see [12].
2
ꢀ 2013 Verlag Helvetica Chimica Acta AG, Zꢁrich

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Results and Discussion. – Initially, we investigated the applicability of 1 as a catalyst
for the cross-coupling reaction of p-bromotoluene and PhB(OH)2 (Table 1). While the
dinuclear Pd complexes 1 catalyzed the reaction to give expected p-2 as a major
product, unexpectedly, the reaction also afforded cine-substitution product m-2. The
ratio m-2/p-2 was affected by ligands of 1. In the reaction with hydroxo-bridged
complex 1a, the total yield of 2 was high, and the ratio of m-2 was low (Entry 1). In
contrast, the ratio of m-2 was higher, and the total yield was moderate in the reaction
with halogeno-bridged complexes 1b – 1d (Entries 2 – 4). The formation of m-2 was
restrained in the reaction with methyl, cinnamyl, and chloro complexes 1f – 1h
Table 1. SuzukiꢀMiyaura Coupling of p-Bromotoluene and PhB(OH)2 in the Presence of Dinuclear Pd
Complexes 1a)
Entry
Catalyst
p-2/m-2b)
Yield [%]b)
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
95 : 5
77: 23
70 : 30
75 : 25
69 : 31
99 : 1
98 : 2
100 : 0
–
80
39
44
58
23
70
28
73
0
[Pd(Me)(dpfam)]
a) A mixture of p-bromotoluene (0.5 mmol) and PhB(OH)2 (0.5 mmol) in benzene (2.0 ml) was stirred
at 1008 for 17 h in the presence of a Pd complex (0.01 mmol) and K2CO3 (1.5 mmol). b) Determined by
GC.

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(Entries 6 – 8). No ortho-isomer of 2 was observed in all reactions. In the case that the
yield of 2 was low or moderate, reasonable amounts of p-bromotoluene remained
unreacted; dehalogenation was not a main side reaction. No products were obtained in
the reactions without a catalyst or with a mononuclear complex [2], which has the same
chelate-bridging ligand, dpfam (Entry 9). Therefore, two Pd centers in 1 seem to be
essential for the formation of cine-substitution product m-2.
In Table 2, the results of the reaction of various monosubstituted bromobenzenes
with PhB(OH)2 in the presence of 1b for 17 h (Table 2) are shown. All reactions were
not complete at that point, and bromoarenes were still present to a greater or lesser
extent. In all reactions of para-substituted bromobenzenes except for 1-bromo-4-
nitrobenzene, cine-substitution was observed (Entries 1 – 8). The ratio of the cine-
substitution products (meta-isomer) was not correlated with the electronic property of
substituents, and was in the range of 25% in most reactions. No tele-substitution
product (ortho-isomer) was detected in all reactions. The reactions of meta-substituted
bromobenzenes afforded results similar to those of para-substituted bromobenzenes
(Entries 9 – 15). The electronic properties of substituents did not affect the ratio of the
cine-substitution products (para-isomer), which was ca. 20% except for the reaction of
1-bromo-3-nitrobenzene (Entry 15). Another possible cine-substitution product, ortho-
isomer, was not formed probably due to steric hindrance. In the reactions of ortho-
substituted bromobenzenes, the ratio of cine-substitution products (meta-isomer)
varied depending upon the substituents. The reactions of o-bromotoluene, o-bromo-
1,1’-biphenyl, and methyl o-phenylbenzoate afforded cine-substitution products (meta-
isomers) in selectivities similar to those of para- and meta-substituted bromobenzenes
(Entries 17 – 19). A MeO group raised the selectivity for the cine-substitution product
m-3 to 48% (Entry 16). In contrast, an Ac group inhibited cine-substitution probably
due to chelation (Entry 20).
Aryl iodides, which are more reactive than aryl bromides in most cross-coupling
reactions, were unreactive in the SuzukiꢀMiyaura coupling catalyzed by 1b. In the
reaction of p-iodoanisole or p-iodoacetophenone, only trace amounts of 4 or 7 were
formed, and the aryl iodides were recovered. Chloroanisole, anisyl triflate, and anisyl
tosylate were also unreactive. The coupling reaction catalyzed by 1b proceeded only
with aryl bromides.
Reaction media were found to exert considerable influence upon the product ratio
and the yield. The cine-substitution took place exclusively in aromatic solvents
(Table 3). The reaction of p-bromotoluene in 1,4-dioxane or 1,2-dichloroethane
afforded only the expected product p-2 (Entries 1 and 2). The cross-coupling reaction
with 1b did not proceed in THF, DMF, octane, or cyclohexane. Remarkable differences
among aromatic solvents were observed. Methylbenzenes such as toluene, xylene, and
mesitylene increased the yield of 2 and decreased the ratio of m-2 (Entries 4 – 6). Other
aromatic solvents such as anisole, chlorobenzene, and ethyl benzoate provieded
moderate selectivities for m-2 with moderate yields (Entries 7 – 10).
The results collected in Table 3 indicated that the reactions that gave 2 in higher
yield exhibited lower selectivity for m-2. To elucidate a correlation between the yield
and the product ratio, the time course of them in the reaction of p-bromotoluene in
PhCl was studied (Fig. 1). The ratio of m-2 gradually decreased with the progress of the
reaction, presumably due to ipso-substitution by mononuclear Pd complexes that

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Table 2. SuzukiꢀMiyaura Coupling of Various Aryl Bromides (X ¼ Br) Catalyzed by 1ba)
Entry
R
Isomer ratio of 3 – 9b)
Yield [%]c)
para
meta
ortho
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
p-Me2N
p-MeO
p-Me
p-Cl
p-MeOOC
p-Ac
76
75
77
77
65
84
77
> 99
25
18
22
17
18
13
3
24
25
23
23
35
16
23
< 1
75
82
78
83
82
87
97
48
28
30
31
8
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
40
76
39d)
40
47
89
66
37
61
29
34
58
55
74
27
32
45
5
p-CF3
p-NO2
m-MeO
m-Me
m-Cl
m-MeOOC
m-Ac
m-CF3
m-NO2
o-MeO
o-Me
o-Ph
o-MeOOC
o-Ac
0
0e)
0
0
0
52
72
70
69
92
68
82
a) A mixture of an aryl bromide (0.5 mmol) and PhB(OH)2 (0.5 mmol) in benzene (2.0 ml) was stirred at
1008 for 17 h in the presence of 1b (0.01 mmol) and K2CO3 (1.5 mmol). b) Determined by GC before
isolation. c) Total yields of isomers. d) Determined by GC. e) Trace amounts of p-2, which was derived
from 1b, were observed.
dissociate from dpfam by decomposition of dinuclear complex 1b. Considering the
curve of the selectivity, the same amounts of m-2 and p-2 might be formed at the
beginning of the reaction. It is also noteworthy that the reaction catalyzed by 1b began
to afford coupling products 2 after several hours. The induction period was also
observed in the reaction catalyzed by the bromo-bridged complex 1c. A complex with
aryl and halogen ligands [PdAr(X)Ln] is one of the intermediates in the ordinary
SuzukiꢀMiyaura coupling reaction. Although 1b and 1c contain the similar ArꢀPdꢀX
moiety, they do not seem to be intermediates in the catalytic cycle of the present
coupling reaction. In fact, only small amounts of 2 were furnished by treatment of 1b

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Table 3. Solvent Effect on cine-Substitution in the Reaction of p-Bromotoluenea)
Entry
Solvent
p-2/m-2b)
Yield (%)c)
1
2
3
4
5
6
7
8
9
1,4-Dioxane
1,2-Dichloroethane
Benzene
Toluene
Xylene
Mesitylene
Anisole
Fluorobenzene
Chlorobenzene
Ethyl benzoate
> 99 : < 1
> 99 : < 1
77: 23
96 : 4
98 : 2
99 : 1
85 : 15
84 : 16
78 : 22
82 : 18
14
60
39
64
87
72
61
29
53
62
10
a) A mixture of p-bromotoluene (0.5 mmol) and PhB(OH)2 (0.5 mmol) in solvent (2.0 ml) was stirred at
1008 for 17 h in the presence of 1b (0.01 mmol) and K2CO3 (1.5 mmol). b) Determined by GC.
c) Determined by GC.
Fig. 1. Time dependence of product yield (solid line) and ratio of m-2 (dashed line) in the reaction of p-
bromotoluene catalyzed by 1b
with PhB(OH)2 in the presence or absence of K2CO3 at 1008 for 6 h. However, 1b was
activated by the treatment with PhB(OH)2; no induction period was observed in the
coupling reaction catalyzed by the activated complex.
Results of the pretreatment study are shown in Fig. 2. While the induction period
was also observed in the reaction of o-bromoanisole without the pretreatment (Fig. 2;
*
), the period disappeared by treating 1b with PhB(OH)2 prior to addition of o-
*
bromoanisole (Scheme 1 and Fig. 2, ). Hydroxo-bridged complex 1a was also
transformed by the pretreatment with PhB(OH)2 (Fig. 3). In the reaction catalyzed
by 1a without pretreatment, the ratio of cine-substitution product m-4 was lower than in
*
the reaction catalyzed by 1b (^ in Fig. 3 and in Fig. 2). In contrast, the reaction with

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Fig. 2. Time dependence of product yield (solid line) and ratio of m-4 (dashed line) in the reaction of o-
*
*
bromoanisole catalyzed by 1b without pretreatment ( ) and with pretreatment ( ), and by 1c without
pretreatment (~)
the pretreatment afforded m-4 with moderate selectivity, which was similar to that in
*
the 1b-catalyzed reaction (^ in Fig. 3 and in Fig. 2). The time dependence of the
yield was also similar to that in the reaction catalyzed by 1b with pretreatment. These
results indicated that the same intermediate was formed by the pretreatment of 1a and
1b with PhB(OH)2. Since no cine-substitution product was obtained in the reaction
using mononuclear complexes bearing or not bearing dpfam such as [Pd(dpfam)(Me)]
or [Pd(PPh3)4], respectively, the common intermediate probably have a dinuclear
structure supported by dpfam. Isolation of the intermediate has not been achieved due
to difficulty in separation from the excess PhB(OH)2.
Scheme 1. Reaction with Pretreatment of 1 with PhB(OH)2 and K2CO3
To determine a source of a H-atom in ipso-position of the cine-substitution
products, the reaction of o-bromoanisole with PhB(OH)2 as conducted in (D6)benzene.
As shown in Scheme 2, the ipso-position of m-4 was highly deuterated. It is obvious that
the ipso-H-atom was derived from aromatic solvents and not from 1,2-shift of the cine-
H-atom. Unexpectedly, H/D exchange reactions occurred in various positions of

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Fig. 3. Time dependence of product yield (solid line) and ratio of m-4 (dashed line) in the reaction of
o-bromoanisole catalyzed by 1a without pretreatment (^) and with pretreatment (^)
benzene rings in m-4, o-4, and recovered o-bromoanisole. Deuteration of unreacted
PhB(OH)2 was not verified, because it could not be isolated from the mixture and
analyzed by GC/MS. All MeO-substituted benzene rings were similarly deuterated,
except for the cine- and ipso-positions. The D ratio in cine-position of o-4 was higher
than that of recovered o-bromoanisole. The H/D exchange did not occur in the reaction
catalyzed by [Pd(PPh3)4], and the reaction without 1b or K2CO3 or PhB(OH)2.
Scheme 2. Reaction of o-Bromoanisole in (D6)Benzene
The above results indicate that the mechanism of the reaction with 1b is rather
different from that of the reaction with ordinary Pd catalysts, although details are still
unclear. Since the ipso-position of m-4 and the cine-position of o-4 were highly
deuterated, the reaction probably proceeded via a m2-aryne or m-o-arylene complex
[13]. Since part of o-4 was formed via the normal mechanism catalyzed by mononuclear
Pd complexes, the cine-position of o-4 could be less deuterated than the ipso-position of
m-4. One of possible routes for formation of the dinuclear aryne complex 13 is hydride
elimination of arylpalladium complex 11 formed by oxidative addition of o-
bromoanisole (10) to Pd (Scheme 3, Route A) [13]. However, it does not seem likely,

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Helvetica Chimica Acta – Vol. 96 (2013)
because 1b or 1c, which have the ArꢀPdꢀX moiety, are not intermediates in the present
reaction. Considering that the H/D exchange occurred at various positions of aromatic
rings, another possible route is elimination of Br from arylpalladium complex 12
formed by CꢀH palladation (Route B) [3a]3). This mechanism is similar to that of the
established aryne formation from aryl halides and strong bases, and consistent with
higher reactivity of aryl bromides than aryl iodides [15]. The aryne complex 13 would
react with PhB(OH)2 to give phenylaryl complex 14 [16], and then the complex 14
would be deuterated via the H/D exchange with (D6)benzene [17].
Scheme 3. Proposed Mechanism
Conclusions. – We found that the SuzukiꢀMiyaura coupling reaction catalyzed by
dinuclear Pd complexes 1 gave cine-substitution products, along with expected
products. Dinuclear structure could be essential for the formation of cine-substitution
products, because a mononuclear Pd complex bearing dpfam, which is formed by
cleavage of 1, is not effective. Although the precise mechanism for the cine-substitution
has remained unclear, it is different from that for the ordinary SuzukiꢀMiyaura
coupling. The results of the reaction in (D6)benzene indicated a mechanism via aryne
3
)
Aryne complexes are generated by ortho-CꢀH bond activation, followed by decarboxylation of
benzoic acids [14].

Helvetica Chimica Acta – Vol. 96 (2013)
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or arylene complexes. Time-course experiments showed that the ratio of cine-
substitution products gradually decreased, probably due to the ipso-substitution by
mononuclear phosphine-free Pd complexes generated by decomposition of 1. Further
improvement of the stability of the dinuclear structure is necessary for elucidation of
the precise reaction mechanism, which will lead to new developments in catalytic
transformation of organic compounds.
Experimental Part
General. Aryl halides and PhB(OH)2 were purchased from Aldrich and TCI and used without
further purification. The complexes 1a – 1c were prepared according to literature methods [2][3].
Spectroscopic recordings were carried out with the following instruments: JEOL FT/IR-350 (FT-IR),
Bruker DPX-400 and DRX-500 (1H- and 13C-NMR), and Shimadzu GCMS-QP5050A (MS).
General Procedure for the Reaction of Aryl Bromides with PhB(OH)2 Catalyzed by 1. To a mixture of
1 (0.010 mmol), PhB(OH)2 (0.50 mmol), and K2CO3 (1.5 mmol) were added benzene (2.0 ml) and then
an aryl bromide (0.50 mmol) in a pressure vial. After heating at 1008 for 17 h, the mixture was cooled to
r.t. and filtered through a short plug of SiO2 with Et2O as eluent. The ratio of regioisomers was
determined by a GC analysis of the filtrate. After evaporation of volatiles, a mixture of 1,1’-biphenyls 2 –
9 was separated from the residue by column chromatography (CC; SiO2 hexane/AcOEt). Compounds 2
[18], 3 [19], 4 [20], 5 [21], 6 [22], 7 [23 – 25], 8 [22][26], and 9 [27] were identified by comparison of their
spectroscopic data with those in the literature.
Evaluation of Time Courses of the Yield and Ratio of p-2 and m-2. To a mixture of 1b (0.015 mmol),
PhB(OH)2 (0.75 mmol), and K2CO3 (2.3 mmol) were added PhCl (3.0 ml), p-bromotoluene
(0.75 mmol), and then dodecane (0.5 mmol) as an internal standard, in a pressure vial. While the
mixture was heated at 1008, a small portion (ca. 10 ml) of the mixture was syringed periodically, diluted by
Et2O, and analyzed by GC.
Reactions after Pretreatment of 1 with PhB(OH)2 and K2CO3. To a mixture of 1 (0.015 mmol),
PhB(OH)2 (0.75 mmol), and K2CO3 (2.3 mmol) were added PhCl (3.0 ml) in a pressure vial. After
stirring the mixture for 6 h at 1008, o-bromoanisole (10; 0.75 mmol) and dodecane were added to the
mixture. While the mixture was heated at 1008, a small portion (ca. 10 ml) of the mixture was syringed
periodically, diluted by Et2O, and analyzed by GC.
Reaction of 10 in (D6)Benzene. To a mixture of 1b (0.010 mmol), PhB(OH)2 (0.50 mmol), and
K2CO3 (1.5 mmol) were added (D6)benzene (2.0 ml) and then 10 (0.50 mmol) in a pressure vial. After
heating at 1008 for 17 h, the mixture was cooled to r.t. and filtered through a short plug of SiO2 with Et2O
as eluent. Recovered 10, o-4, and m-4 were separated by prep. GC (Uniport 80/100 silicone SE-30 15%, 6
1
f ꢁ 3 m). Their deuteraion degrees were determined by their H-NMR spectra.
REFERENCES
[1] H. Steinhagen, G. Helmchen, Angew. Chem., Int. Ed. 1996, 35, 2339; E. K. van den Beuken, B. L.
Feringa, Tetrahedron 1998, 54, 12985; G. J. Rowlands, Tetrahedron 2001, 57, 1865; ꢂMultimetallic
Catalysis in Organic Synthesisꢃ, Eds. M. Shibasaki, Y. Yamamoto, Wiley-VCH, Weinheim, 2004.
[2] N. Tsukada, O. Tamura, Y. Inoue, Organometallics 2002, 21, 2521.
[3] a) N. Tsukada, T. Mitsuboshi, H. Setoguchi, Y. Inoue, J. Am. Chem. Soc. 2003, 125, 12102; b) N.
Tsukada, K. Murata, Y. Inoue, Tetrahedron Lett. 2005, 46, 7515; c) N. Tsukada, H. Setoguchi, T.
Mitsuboshi, Y. Inoue, Chem. Lett. 2006, 35, 1164; d) N. Tsukada, S. Ninomiya, Y. Aoyama, Y. Inoue,
Org. Lett. 2007, 9, 2919.
[4] N. Tsukada, Y. Ohba, Y. Inoue, J. Organomet. Chem. 2003, 687, 436; N. Tsukada, M. Wada, N.
Takahashi, Y. Inoue, J. Organomet. Chem. 2009, 694, 1333; N. Tsukada, A. Takahashi, Y. Inoue,
Tetrahedron Lett. 2011, 52, 248.
´
´
[5] J. Suwinski, K. Swierczek, Tetrahedron 2001, 57, 1639.

1102
Helvetica Chimica Acta – Vol. 96 (2013)
[6] K. Kikukawa, H. Umekawa, T. Matsuda, J. Organomet. Chem. 1986, 311, C44; G. Stork, R. C. A.
Isaacs, J. Am. Chem. Soc. 1990, 112, 7399; V. Farina, M. A. Hossain, Tetrahedron Lett. 1996, 37, 6997;
A. Flohr, Tetrahedron Lett. 1998, 39, 5177; X. Han, B. M. Stoltz, E. J. Corey, J. Am. Chem. Soc. 1999,
121, 7600; E. Fillion, N. J. Taylor, J. Am. Chem. Soc. 2003, 125, 12700; K.-S. Masters, B. L. Flynn, Adv.
Synth. Catal. 2009, 351, 530; Y. Peng, W.-D. Z. Li, Eur. J. Org. Chem. 2010, 6703.
[7] K. Ikenaga, S. Matsumoto, K. Kikukawa, T. Matsuda, Chem. Lett. 1990, 19, 185; Y. Hatanaka, K.-i.
Goda, T. Hiyama, J. Organomet. Chem. 1994, 465, 97; J. C. Anderson, S. Anguille, R. Bailey, Chem.
Commun. 2002, 2018.
[8] D. S. Ennis, T. L. Gilchrist, Tetrahedron Lett. 1989, 30, 3735; A. L. Hansen, J.-P. Ebran, T. M. Gøgsig,
T. Skrydstrup, J. Org. Chem. 2007, 72, 6464; A. T. Lindhardt, T. M. Gøgsig, T. Skrydstrup, J. Org.
Chem. 2009, 74, 135.
[9] A. L. Hansen, J.-P. Ebran, M. Ahlqust, P.-O. Norrby, T. Skrydstrup, Angew. Chem., Int. Ed. 2006, 45,
3349; J.-P. Ebran, A. L. Hansen, T. M. Gøgsig, T. Skrydstrup, J. Am. Chem. Soc. 2007, 129, 6931.
[10] K. Yoshida, T. Hayashi, J. Am. Chem. Soc. 2003, 125, 2872; J.-Y. Yu, R. Shimizu, R. Kuwano, Angew.
Chem., Int. Ed. 2010, 49, 6396.
[11] D. A. Watson, M. Su, G. Teverovskiy, Y. Zhang, J. Garcꢄa-Fortanet, T. Kinzel, S. L. Buchwald,
Science 2009, 325, 1661.
[12] A. Maehara, H. Tsurugi, T. Satoh, M. Miura, Org. Lett. 2008, 10, 1159; S. Mochida, K. Hirano, T.
Satoh, M. Miura, Org. Lett. 2010, 12, 5776; J. Cornella, M. Righi, I. Larrosa, Angew. Chem., Int. Ed.
2011, 50, 9429; M. Catellani, Synlett 2003, 298.
[13] M. A. Bennett, H. P. Schwemlein, Angew. Chem., Int. Ed. 1989, 28, 1296.
[14] A. A. Cant, L. Roberts, M. F. Greaney, Chem. Commun. 2010, 46, 8671.
[15] J. D. Roberts, D. A. Semenow, J. Howard E. Simmons, L. A. Carlsmith, J. Am. Chem. Soc. 1956, 78,
601.
[16] C. H. Oh, H. H. Jung, K. S. Kim, N. Kim, Angew. Chem., Int. Ed. 2003, 42, 805.
[17] J. Atzrodt, V. Derdau, T. Fey, J. Zimmermann, Angew. Chem., Int. Ed. 2007, 46, 7744.
[18] M. E. Mowery, P. Deshong, J. Org. Chem. 1999, 64, 3266.
´
´
[19] C. Najera, J. Gil-Molto, S. Karlstrçm, L. R. Favello, Org. Lett. 2003, 5 1451.
[20] M. Lukeman, P, Wan, J. Am. Chem. Soc. 2002, 124, 9458.
[21] H.-J. Lehmler, L. W. Robertson, Chemosphere 2001, 45, 137.
[22] S.-K. Kang, J.-S. Kim, S.-K. Yoon, K.-H. Lim, S. S. Yoon, Tetrahedron Lett. 1998, 39, 3011.
[23] D. L. Clive, S. Kang, J. Org. Chem. 2001, 66, 6083.
[24] L. Zhu, J. Duquette, M. Zhang, J. Org. Chem. 2003, 68, 3729.
[25] S. Schneider, W. Bannwarth, Helv. Chim. Acta 2001, 84, 735.
[26] J. Hassan, C. Hathroubi, C. Gozzi, M. Lemaire, Tetrahedron 2001, 37, 7845.
[27] A. Zapf, M. Beller, Chem. – Eur. J. 2000, 6, 1830.
Received August 11, 2012