Palladium-catalyzed domino Mizoroki-Heck/intermolecular C(sp3)-H activation sequence: An approach to the formation of C(sp3)-C(sp3) bonds

Article abstract of DOI:10.1002/ejoc.201500116

A palladium-catalyzed domino Mizoroki-Heck/intermolecular unactivated C(sp³)-H alkylation reaction has been developed. This simple palladium nanoparticle catalytic system shows good activity and affords the dimeric dihydrobenzofuran derivatives

Full text of DOI:10.1002/ejoc.201500116

SHORT COMMUNICATION
DOI: 10.1002/ejoc.201500116
Palladium-Catalyzed Domino Mizoroki–Heck/Intermolecular C(sp3)–H
Activation Sequence: An Approach to the Formation of C(sp3)–C(sp3) Bonds
Wei Wang,[a] Rong Zhou,[a] Zhi-Jie Jiang,[a] Xin Wang,[a] Hai-Yan Fu,[a] Xue-Li Zheng,[a]
Hua Chen,[a] and Rui-Xiang Li*[a]
Keywords: C-H activation / Cross-coupling / Dihydrobenzofuran / Domino reactions / Mizoroki–Heck reaction / Palladium
A
palladium-catalyzed domino Mizoroki–Heck/intermo-
benzofuran derivatives in moderate to good yields. Further-
lecular unactivated C(sp3)–H alkylation reaction has been more, this reaction provides a new method for the elabora-
developed. This simple palladium nanoparticle catalytic sys-
tem shows good activity and affords the dimeric dihydro-
tion of domino reactions involving a C(sp3)–C(sp3) bond-
forming process.
no reports have appeared where domino processes involving
a challenging intermolecular C(sp3)–H activation has been
used.
Introduction
The rapid construction of complex heteroatom-contain-
ing molecular skeletons has become an attractive challenge
in the past years. For this reason, domino reactions have
proven to be an appealing and highly efficient strategy for
the rapid formation of multiple bonds in organic synthe-
sis.[1] In recent years, the transition-metal-catalyzed trans-
formation of C–H bonds has emerged as one of the most
promising and powerful methods for the construction of C–
C bond frameworks.[2] In contrast with the better developed
cross-dehydrogenative-coupling (CDC) reactions of C(sp)–
H[3] and C(sp2)–H[4] bonds, the alkylation of unactivated
and nonacidic C(sp3)–H[5] bonds remains one of the most
challenging tasks in the field of C–H activation.[6]
In connection with more interest in the development of
domino processes involving C–H activation as a key step,
an impressive series of efficient procedures and novel meth-
odologies have been devised and successfully applied to the
synthesis of a variety of structures including dihydrobenzo-
furans,[7] indolines,[7] isoindoles,[8] spirooxindoles,[9] spirohy-
droquinolins,[10] and spiropentacyclic compounds.[11] For
example, the (alkyl)PdII halide intermediate in the intramo-
lecular Mizoroki–Heck (MH) reaction can undergo an in-
tramolecular or intermolecular direct arylation to form a
second new bond (Scheme 1a and b).[7,9a,10] More recently,
Zhu et al. reported the first example of a palladium(0)-cata-
lyzed domino carbopalladation/intramolecular C(sp3)–
C(sp3) bond-forming process by an alkylpalladium(II) in-
termediate (Scheme 1c).[9b] To the best of our knowledge,
Results and Discussion
Herein, we report the first simple and efficient palla-
dium-catalyzed domino cyclization involving carbopallad-
ation and the subsequent intermolecular functionalization
of an unactivated C(sp3)–H bond for the preparation of di-
meric dihydrobenzofuran derivatives. The underlying prin-
ciple is shown in Scheme 2. Intramolecular MH reaction of
arene 1 would give 2,3-dihydrobenzofuran 2a and (alkyl)-
PdII intermediate A. The intermediate A, being sufficiently
stable and ideally positioned, should be able to activate the
C(sp3)–H bond of 2a by the auxiliary coordination of the
oxygen atom on the furan ring, thus leading to a dimeric
dihydrobenzofuran product 3aa by the sequential CDC re-
action.
Particular interest in palladium-catalyzed MH reac-
tions[12] prompted us to study the domino cyclization reac-
tion involving the CDC transformation of C(sp3)–H bonds
by using palladium nanoparticle catalysts. To test our strat-
egy, we tried to synthesize 3,3-dimethyl-2,3-dihydrobenzo-
furan (2a) and dimer 3aa from 1-iodo-2-(2-methylprop-2-
enyloxy)benzene (1a) by a domino reaction, where the MH
and CDC reactions took place sequentially (Table 1). Prod-
uct 3aa was a crystalline solid, and single-crystal X-ray dif-
fraction confirmed the exact structure.[13] Initial screening
of palladium sources was carried out by treating 0.5 mmol
of 1a with 2 mol-% of palladium, 1 equiv. of (nBu)4NBr
(TBAB) and 2 equiv. of K3PO4 in N,N-dimethylacetamide
(DMA) at 120 °C under nitrogen for 24 h. To our delight,
all of palladium precursors exhibited good activity and af-
forded a mixture of 2a and 3aa in 55–90% yields (Table 1,
[a] Key Lab of Green Chemistry and Technology, Ministry of
Education; College of Chemistry, Sichuan University,
Chengdu 610064, China
E-mail: liruixiang@scu.edu.cn
http://chem.scu.edu.cn/
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201500116.
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R.-X. Li et al.
SHORT COMMUNICATION
Scheme 1. Precedent in domino Mizoroki–Heck/C–H activation involving alkylpalladium(II) intermediates and the formation of new C–
C bonds.
Having identified the optimal palladium source, we scre-
ened a wide range of bases and solvents (Table 2). K3PO4
was found to be the most efficient, and the product yield
was significantly affected by the nature and amount of the
base (Table 2, Entries 1–9). Solvent screening (Table 2, En-
tries 10–16) showed that cyclizing compound 2a could be
achieved in up to 100% yield in n-butanol,[14] and DMA
was a best solvent with regard to the yield of 3aa. Based on
these optimization studies, further reactions were per-
formed at 120 °C under nitrogen using [Pd(COD)Cl2]
(2 mol-%), TBAB (1 equiv.), and K3PO4 (3 equiv.) in DMA.
activation.
Scheme 2. Proposed domino reaction involving a C(sp3)–H bond
The scope and generality of this method was investigated
using a variety of substrates 1a–f (Scheme 3). The method
tolerates various electronic and substitution patterns on the
aromatic moieties, affording dimeric dihydrobenzofuran de-
rivatives 3aa–ee[15] in moderate to good yields (Scheme 3).
Entries 1–6). Moreover, using [Pd(COD)Cl2] as the catalyst,
Exceptions are reactions involving substrates having an or-
tho-substituted aryl halide fragment (e.g. 1f). To our de-
light, the domino reaction with less active aryl bromides
also gave the corresponding products under our optimized
reaction conditions.
we obtained the desired CDC product 3aa in the best yield
(54%). It is noteworthy that TBAB is not essential to the
C(sp3)–H activation, but its presence could improve the
yield of 3aa (Table 1, Entry 7). No product 3aa was ob-
served in the absence of the palladium precursor (Table 1,
Entry 8). Furthermore, transmission electron microscopy
An interesting question is whether two different dihydro-
(TEM) imaging demonstrated that palladium is present in benzofurans can be connected by C(sp3)–H bond acti-
the form of nanoparticles with an average particle size of vation, which could broaden the scope and utility of this
5.6 nm (Figure 1).
domino processes. To address this issue, aryl iodide 1a was
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Domino Mizoroki–Heck/Intermolecular C(sp3)–H Activation Sequence
Table 1. Effect of catalyst precursors on the domino reaction.[a]
Entry
[Pd]
TBAB [mmol]
Yield of 2a [%][b]
Yield of 3aa [%][b]
1
2
3
4
5
6
7
8
PdCl2
Pd(OAc)2
[Pd(C3H5)Cl]2
Pd2(dba)3
[Pd(PhCN)2Cl2]
[Pd(COD)Cl2]
[Pd(COD)Cl2]
none
0.5
0.5
0.5
0.5
0.5
0.5
0
45
45
44
31
21
36
14
7
43
44
47
33
34
54
45
0
0.5
[a] Reaction conditions: 1a (0.5 mmol), K3PO4 (1 mmol), DMA (1.5 mL), [Pd] (2 mol-%) at 120 °C under nitrogen for 24 h. [b] Yields
1
are determined by GC–MS and H NMR spectroscopy.
Figure 1. TEM micrographs and nanoparticle size distributions: [Pd(COD)Cl2] as catalyst precursor and reaction for 1 h. Reaction
conditions: 1a (0.5 mmol), [Pd(COD)Cl2] (0.01 mmol), K3PO4 (1.5 mmol), DMA (1.5 mL), TBAB (0.5 mmol), under nitrogen, 100 °C.
allowed to react with aryl bromides 1b–d under the opti- action, and the product 3aa was obtained in 65% yield.
mized conditions. The desired products 4ab–ad were gener- Importantly, the system also worked well when the reaction
ated in moderate yields (Table 3, Entries 1–3). Meanwhile, was conducted in the dark (see the Supporting Infor-
the homocoupling products 3aa–dd were also generated un- mation). These results indicated that a radical mecha-
der our conditions. We were pleased to note that two less nism[6c–6e] was not involved in these transformations.
active aryl bromides 1b–d also reacted well to afford the Furthermore, according to the curve of conversion vs. time,
desired products 4bc–cd in moderate yields (Table 3, En- the content of 2a increased gradually at the beginning of
tries 4–6). To further illustrate the generality of our method, the reaction and decreased after 12 h, while the amount of
we applied this strategy to the domino reaction of 1-iodo- 3aa increased sharply (Figure 2). The total content of 2a
2-(3-methylbut-3-enyloxy)benzene (Scheme 4). To our sur- and 3aa did not change after 12 h, indicating that 2a may
prise, the desired dimer was not observed, and tetracyclic participate in this reaction. What is more, the yield of 3aa
compound 5 resulting from twofold C–H functionalizations increased to 85% when 2a (0.5 mmol) reacted with 1a
was obtained in 70% yield.[16]
(0.5 mmol) under otherwise identical conditions. In ad-
To gain insight into the palladium-catalyzed domino re- dition, attempts to achieve the desired product 3aa failed
action, several control experiments were carried out to elu- by using 2a as reaction substrate, whereas the products 4ab
cidate the process. Adding the radical inhibitor 2,2,6,6-tet- (4%) and 3bb (57%) were obtained when 2a reacted with
ramethyl-1-piperidinoxyl (TEMPO) did not inhibit the re- 1b (3aa was not observed). An increase in the yield of cross-
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R.-X. Li et al.
SHORT COMMUNICATION
Table 2. Optimization of palladium-catalyzed domino reaction of
Table 3. Scope of the palladium-catalyzed domino reaction of dif-
ferent substrates.[a]
1a.[a]
Entry
Base
Solvent
Temp. Yield of 2a Yield of 3aa
[°C]
[%][b]
[%][b]
1
2
3
4
5
Na2CO3
K2CO3
Cs2CO3
CsF
K3PO4
K3PO4
K3PO4
NaOH
tBuOLi
K3PO4
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMA
DMA
toluene
120
120
120
120
120
120
120
120
120
100
100
100
100
100
130
130
13
24
25
39
36
38
23
11
27
21
31
100
30
23
38
48
0
5
4
12
54
55
66
6
37
17
18
0
25
27
54
42
6[c]
7[d]
8
9
10
11
12
13
14
15
16
K3PO4 1,4-dioxane
K3PO4
K3PO4
K3PO4
K3PO4
K3PO4
n-butanol
DMF
DMA
DMA
NMP
[a] Reaction conditions: 1a (0.5 mmol), TBAB (0.5 mmol), base
(1 mmol), solvent (1.5 mL), [Pd(COD)Cl2] (2 mol-%) under nitro-
1
gen for 24 h. [b] Yields are determined by GC–MS and H NMR
spectroscopy. [c] 48 h. [d] K3PO4 (1.5 mmol).
[a] Reaction conditions: Substrate 1 (0.5 mmol), substrate 2
(0.5 mmol), TBAB (1 mmol), K3PO4 (2.5 mmol), DMA (2.5 mL),
[Pd(COD)Cl2] (4 mol-%) at 120 °C under nitrogen for 24 h. [b] Iso-
lated yields (yield of 4 is reported with respect to 0.5 mmol of 1).
[c] [Pd(COD)Cl2] (5 mol-%).
Scheme 3. Scope of the palladium-catalyzed domino reaction in-
volving C(sp3)–H activation. Reaction conditions: see Table 2, En-
try 7. Yields of isolated products.
coupling products 4ac (14%) or 4ad (16%) was observed
when 2a reacted with 1c or 1d.[17] These results suggest that reaction, coordinates with the product 2a. The resulting
2a indeed participated in the step of C(sp3)–H activation, complex B undergoes reversible cyclometalation to give C,
and the alkylpalladium halide intermediate may be crucial probably by a concerted metalation deprotonation mecha-
to this domino reaction.
nism. The PdII intermediate C readily should undergo a re-
The exact mechanism of this reaction is not clear at pres- ductive elimination to regenerate the Pd0 complex and con-
ent. However, on the basis of these preliminary results and comitantly release the desired product 3aa. Gratifyingly,
the literature reports,[9b,18,19] a plausible pathway for this ESI-MS studies indicated that the alkylpalladium com-
domino reaction was proposed (Scheme 5). The (alkyl)PdII plexes A and C were formed (for details, see the Supporting
halide intermediate A, generated from intramolecular MH Information).
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Domino Mizoroki–Heck/Intermolecular C(sp3)–H Activation Sequence
Scheme 4. Palladium-catalyzed domino reaction involving two C–H functionalizations. Reaction conditions: iodoarene (0.5 mmol), TBAB
(1 equiv.), K3PO4 (3 equiv.), DMA (1.5 mL), [Pd(COD)Cl2] (2 mol-%) at 120 °C under nitrogen for 24 h.
Conclusions
We have reported a simple and efficient palladium-cata-
lyzed domino reaction involving the functionalization of
C(sp3)–H bonds. This catalytic reaction provides an ef-
ficient method for the synthesis of dimeric dihydrobenzofu-
rans from simple starting materials. Importantly, this strat-
egy first realizes a domino process involving a challenging
intermolecular unactivated C(sp3)–H alkylation.
Experimental Section
Representative Procedure for 3aa: K3PO4 (1.5 mmol), TBAB
(0.5 mmol), and [Pd(COD)Cl2] (2.85 mg, 0.01 mmol) were added
into a dried Schlenk tube with a magnetic bar, which was subjected
to evacuation/flushing with dry nitrogen five times, and then 1a
(0.5 mmol) and DMA (1.5 mL) were added successively to it. The
reaction mixture was heated at 120 °C for 24 h with stirring. After
standard workup procedures (see the Supporting Information), the
crude product was purified by silica gel chromatography, and 3aa
was isolated as white solid (46.3 mg, 0.158 mmol, 63%).
Figure 2. Conversion vs. time plot for the domino reaction of 1a.
Reaction conditions: see Table 2, Entry 7. Yields are determined by
GC–MS, and biphenyl is an internal standard.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental details, characterization data, and copies of the
1H NMR and 13C NMR spectra of all key intermediates and final
products.
Acknowledgments
We gratefully acknowledge the National Natural Science Founda-
tion of China (No. 21202104).
[1] a) S. Ikeda, Acc. Chem. Res. 2000, 33, 511; b) F. Lieby-Muller,
J. Rodriguez Jean, J. Am. Chem. Soc. 2005, 127, 17176; c) Z.-
Y. Lu, C.-M. Hu, J. Li, Y.-X. Cui, Y.-X. Jia, Org. Lett. 2010,
12, 480; d) H. Pellissier, Chem. Rev. 2013, 113, 442; e) D.-C.
Wang, H.-Y. Niu, M.-S. Xie, G.-R. Qu, H.-X. Wang, H.-M.
Guo, Org. Lett. 2014, 16, 262.
[2] For leading reviews, see: a) H. Ohno, M. Yamamoto, M. Iuchi,
T. Tanaka, Angew. Chem. Int. Ed. 2005, 44, 5103; Angew.
Chem. 2005, 117, 5233; b) R. T. Ruck, M. A. Huffman, M. M.
Kim, M. Shevlin, W. V. Kandur, I. W. Davies, Angew. Chem.
Int. Ed. 2008, 47, 4711; Angew. Chem. 2008, 120, 4789; c)
I. A. I. Mkhalid, J. H. Barnard, T. B. Marder, J. M. Murphy,
Scheme 5. Proposed mechanism.
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R.-X. Li et al.
SHORT COMMUNICATION
J. F. Hartwig, Chem. Rev. 2010, 110, 890; d) T. C. Boorman, I.
Larrosa, Chem. Soc. Rev. 2011, 40, 1910.
[11] G. Satyanarayana, C. Maichle-Mössmer, M. E. Maier, Chem.
Commun. 2009, 1571.
[12] a) W. Wang, Q. Yang, R. Zhou, H.-Y. Fu, R.-X. Li, H. Chen,
X.-J. Li, J. Organomet. Chem. 2012, 697, 1; b) W. Wang, R.
Zhou, Z.-J. Jiang, K. Wang, H.-Y. Fu, X.-L. Zheng, H. Chen,
R.-X. Li, Adv. Synth. Catal. 2014, 356, 616.
[13] See the Supporting Information. CCDC-999259 (3aa) contains
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif. The dimeric 3aa (meso and d/l pair) may be
formed according to 1H NMR spectra and crystallographic
data.
[14] Olefin insertion was shown to be fast by running the reaction
under reductive MH conditions, with 100% conversion to com-
pound 2a. See ref.[2b] Further deuterated experiments to ex-
plain the source of the hydrogen of 2a are shown in the Sup-
porting Information.
[15] X-ray structures of 3bb and 3cc are shown in the Supporting
Information. CCDC-1013559 (3cc) and -1013560 (3bb) contain
the supplementary crystallographic data for this paper. These
data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/
data_request/cif.
[16] CCDC-999260 (5) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. A similar reaction was
reported by Lautens et al. just now; see: M. Sickert, H. Wein-
stabl, B. Peters, X. Hou, M. Lautens, Angew. Chem. Int. Ed.
2014, 53, 5147; Angew. Chem. 2014, 126, 5247. The process
provides a very efficient way to synthesize fused ring systems.
Further studies to extend the scope and clarify the mechanism
are currently underway.
[17] 2a (0.25 mmol), TBAB (1 equiv.), K3PO4 (2 equiv.), DMA
(1 mL), [Pd(COD)Cl2] (2 mol-%) at 120 °C for 24 h; 1b–d
(0.25 mmol), 2a (1 equiv.), TBAB (2 equiv.), K3PO4 (6 equiv.),
DMA (1.5 mL), [Pd(COD)Cl2] (4 mol-%) at 120 °C for 24 h.
[18] Palladium-catalyzed phenol-directed C–H activation: a) X.-S.
Wang, Y. Lu, H.-X. Dai, J.-Q. Yu, J. Am. Chem. Soc. 2010,
132, 12203; b) B. Xiao, T.-J. Gong, Z.-J. Liu, J.-H. Liu, D.-F.
Luo, J. Xu, L. Liu, J. Am. Chem. Soc. 2011, 133, 9250.
[19] Nickel-catalyzed direct arylation of C(sp3)–H bonds: a) Y. Aih-
ara, N. Chatani, J. Am. Chem. Soc. 2013, 135, 5308; b) Y. Aih-
ara, N. Chatani, J. Am. Chem. Soc. 2014, 136, 898.
Received: January 25, 2015
[3]
For selected examples of C(sp)–H functionalizations, see: a) L.
Zhao, C.-J. Li, Angew. Chem. Int. Ed. 2008, 47, 7075; Angew.
Chem. 2008, 120, 7183; b) C. A. Correia, C.-J. Li, Adv. Synth.
Catal. 2010, 352, 1446; c) M. O. Ratnikov, M. P. Doyle, J. Am.
Chem. Soc. 2013, 135, 1549; d) L. Ackermann, Acc. Chem. Res.
2014, 47, 281.
For recent reviews of C(sp2)–H functionalizations, see: a) D. A.
Colby, R. G. Bergman, J. A. Ellman, Chem. Rev. 2010, 110,
624; b) L. Ackermann, Chem. Rev. 2011, 111, 1315; c) J. Yama-
guchi, A. D. Yamaguchi, K. Itami, Angew. Chem. Int. Ed. 2012,
51, 8960; Angew. Chem. 2012, 124, 9092; d) P. B. Arockiam, C.
Bruneau, P. H. Dixneuf, Chem. Rev. 2012, 112, 5879; e) B. Li,
P. H. Dixneuf, Chem. Soc. Rev. 2013, 42, 5744.
For selected reviews on C(sp3)–H functionalizations, see: a) O.
Daugulis, H.-Q. Do, D. Shabashov, Acc. Chem. Res. 2009, 42,
1074; b) T. W. Lyons, M. S. Sanford, Chem. Rev. 2010, 110,
1147; c) O. Baudoin, Chem. Soc. Rev. 2011, 40, 4902; d) T. R.
Newhouse, P. S. Baran, Angew. Chem. Int. Ed. 2011, 50, 3362;
Angew. Chem. 2011, 123, 3422; e) B.-J. Li, Z.-J. Shi, Chem. Soc.
Rev. 2012, 41, 5588; f) J. L. Roizen, M. E. Harvey, J. Du Bois,
Acc. Chem. Res. 2012, 45, 911; g) B. G. Hashiguchi, S. M. Bi-
schof, M. M. Konnick, R. A. Periana, Acc. Chem. Res. 2012,
45, 885; h) M. Corbet, F. D. Campo, Angew. Chem. Int. Ed.
2013, 52, 9896; Angew. Chem. 2013, 125, 10080; i) S. A. Girard,
T. Knauber, C.-J. Li, Angew. Chem. Int. Ed. 2014, 53, 74; An-
gew. Chem. 2014, 126, 76.
For selected examples of C(sp3)–H alkylations, see: a) Z. Li,
C.-J. Li, J. Am. Chem. Soc. 2005, 127, 3672; b) L. Chen, C.-J.
Li, Adv. Synth. Catal. 2006, 348, 1459; c) J. Xie, H. Li, J. Zhou,
Y. Cheng, C. Zhu, Angew. Chem. Int. Ed. 2012, 51, 1252; An-
gew. Chem. 2012, 124, 1278; d) B. Zhang, Y.-X. Cui, N. Jiao,
Chem. Commun. 2012, 48, 4498; e) K. Alagiri, P. Devadig,
K. R. Prabhu, Chem. Eur. J. 2012, 18, 5160; f) S.-Y. Zhang, Q.
Li, G. He, W. A. Nack, G. Chen, J. Am. Chem. Soc. 2013, 135,
12135; g) T. Nobuta, N. Tada, T. Miura, A. Itoh, Org. Lett.
2013, 15, 574; h) G. Rouquet, N. Chatani, Angew. Chem. Int.
Ed. 2013, 52, 11726; Angew. Chem. 2013, 125, 11942.
[4]
[5]
[6]
[7] O. René, D. Lapointe, K. Fagnou, Org. Lett. 2009, 11, 4560.
[8] Y.-M. Hu, C.-L. Yu, D. Ren, Q. Hu, L.-D. Zhang, D. Cheng,
Angew. Chem. Int. Ed. 2009, 48, 5448; Angew. Chem. 2009, 121,
5556.
[9] a) see Ref. 2b; b) T. Piou, L. Neuville, J.-P. Zhu, Angew. Chem.
Int. Ed. 2012, 51, 11561; Angew. Chem. 2012, 124, 11729.
[10] T. Piou, L. Neuville, J.-P. Zhu, Org. Lett. 2012, 14, 3760.
Published Online: March 19, 2015
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