Zinc-catalyzed domino hydroamination-alkyne addition

Article abstract of DOI:10.1002/adsc.201000211

The first zinc-catalyzed one-step synthesis of quaternary propargylamines with four different substituents is described. The domino hydroamination- alkyne addition reaction gives access to functionalized propargylamines under mild conditions.

Full text of DOI:10.1002/adsc.201000211

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DOI: 10.1002/adsc.201000211
Zinc-Catalyzed Domino Hydroamination–Alkyne Addition
Mustafa Biyikal,a Marta Porta,a Peter W. Roesky,b,* and Siegfried Blecherta,*
a
Institut fꢀr Chemie, Technische Universitꢁt Berlin, Strasse des 17. Juni 135, 10623 Berlin, Germany
Fax : (+49)-30-3142-3619; e-mail: blechert@chem.tu-berlin.de
Institut fꢀr Anorganische Chemie, Karlsruher Institut fꢀr Technologie (KIT), Engesserstr. 15, 76128 Karlsruhe, Germany
b
Fax : (+49)-721-608-4854; e-mail: roesky@kit.edu
Received: March 17, 2010; Published online: August 16, 2010
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/adsc.201000211.
Abstract: The first zinc-catalyzed one-step synthesis
of quaternary propargylamines with four different
substituents is described. The domino hydroamina-
tion–alkyne addition reaction gives access to func-
tionalized propargylamines under mild conditions.
verted in a copper-catalyzed reaction to propargyl-
AHCTUNGTRENNUNG
amines having a secondary carbon center.[12] These
copper-catalyzed reactions have been recently de-
scribed with diverse phenylacetylenes.[13] The hydro-
AHCTUNGTRENNUNG
Keywords: alkynes; domino reaction; hydroamina-
tion; metathesis; propargylamines; zinc
ACHTUNGTRENNUNG
Zn/Cd catalyst the Markovnikov addition was ob-
served but only propyne and dimethyl- or diethyl-
AHCTUNGTRENNUNG
amine were used under drastic conditions.[14] Herein
we describe a flexible zinc-catalyzed one-step synthe-
sis of quaternary propargylamines with four different
The synthesis of fine chemicals and natural products substituents. The reaction proceeds under mild condi-
is often a multistep process including salt-generating tions and tolerates different functional groups.
reactions. Nowadays the modern synthesis design de-
During our studies on zinc-catalyzed hydroamina-
mands for efficient techniques to minimize the tions we found that b-diiminate (BDI) complexes like
number of steps towards the product and to avoid the 1 in presence of cocatalyst 2 lead to the catalytically
formation of by-products. Domino and cascade reac- active species 3 (Scheme 1). According to our results,
tions allow an ecologically and economically favoura- the cocatalyst 2 protonates the precatalyst 1 irreversi-
ble synthesis.[1–3] These procedures describe closely bly forming methane and generates the catalyst 3 as a
coupled individual reactions that yield a product in a cationic BDI-zinc complex with a low-coordinating
single process.
triflate anion. We confirmed the molecular structure
The addition of an organic amine to C-C multiple of 3·THF by single crystal X-ray diffraction in the
bonds presents a challenging and demanding topic. solid-state.
The metal-catalyzed hydroamination has been studied
Compound 3 is a good catalyst for hydroamination
with different types of catalysts.[4–7] We have reported of alkynes forming enamines, which should easily lead
the metal-catalyzed hydroamination reactions with a to imines or iminium salts. Since several zinc-cata-
diversity of zinc complexes.[6] Hydroamination reac- lyzed additions of monosubstituted acetylenes to spe-
tions of alkynes often resulted in the formation of un- cial imines have been described,[15] we tested the in-
stable intermediates like enamines and imines and termediately formed 3 for the combined reactions.
hence were reduced to the corresponding amines in a
In the initial experiments we used dibenzylamine
one-pot procedure.[7] Hydroaminations were also and phenylacetylene. A 1/2.5 mixture was treated
combined in a tandem process with several other re-
actions like Cope rearrangement,[8] hydroarylation,[9]
hydrosilylation[10] and with diverse addition reac-
tions.[11] We are interested in a combination of hydro-
amination and alkyne addition in a catalytic domino
process yielding propargylamines. Such a sequence
has not been described intensively and only a few
cases are known. In the first report acetylene was con- Scheme 1. Synthesis of the BDI-zinc catalyst 3.
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Zinc-Catalyzed Domino Hydroamination–Alkyne Addition
with 10 mol% precatalyst 1 and cocatalyst 2 in ben- tributed to its instability in the presence of moisture.
zene-d6 at 608C in a sealed tube. Dibenzylamine was It is proposed that this decomposition reaction is in-
completely consumed after 30 h and the correspond- duced by the aromatic groups of product 6 introduced
ing propargylamine 4 was isolated by flash chroma- by phenylacetylene. We confirmed this assumption by
tography in 72% yield (Table 1, entry 1). When the using 1-octyne instead of phenylacetylene. The
temperature was increased to 808C, the reaction time domino reaction of 1-octyne and with the N-allylic
was reduced to 18 h (Table 1, entry 2). The reactions aniline delivered the propargylamine 7 in 8 h at 608C
were also performed with 1-octyne to verify the possi- in a high yield of 86% (Table 1, entry 6). Decomposi-
bility of a tandem reaction with an aliphatic substitut- tion reaction of the isolated enyne 7 was not ob-
ed alkyne and observed the formation of the corre- served.
sponding propargylamines with high yields in a re-
To expand the substrate scope, we studied more
duced reaction time. The double benzyl-protected challenging substrates and converted amines 8 and 10
propargylamine 5 having aliphatic groups was isolated to the corresponding progargyl derivates 9 and 11
in an even higher yield of 78% (Table 1, entries 3 and with 1-heptyne and 1-octyne (Table 1, entries 7 and
4).
8). In this case the reaction took over 40 h at 808C
We next examined the use N-allylaniline in combi- and, interestingly, the reaction proceeded with com-
nation with phenylacetylene and observed the forma- plete selectivity, and no intramolecular alkene-hydro-
tion of product even at room temperature (Table 1, amination was observed.
entry 5). The low isolated yield of the product 6 is at-
Table 1. Intermolecular domino hydroamination–alkyne addition reactions.
Entry
1
Amine
Cat. loading [mol%]
10
Temp. [8C]
Time [h]
30
Yield [%]
72
Product
60
2
10
80
18
73
3
4
10
1
60
80
12
34
77
78
5
6
10
10
r.t.
60
53
8
87[a]
86
7
10
10
80
80
40
40
61
76
8
[a]
1
Conversion determined by H NMR.
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Mustafa Biyikal et al.
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of TsOH with 3 mol% of Grubbsꢃ I catalyst under an
ethylene atmosphere. After 12 h the expected diene
13, which is a useful precursor for Diels–Alder reac-
tions,[16c,d] was isolated after purification on column
chromatography in 90% yield.
The mechanism of the zinc-catalyzed alkyne addi-
tion reaction is probably similar to that of the copper-
catalyzed reaction.[13] In the first step of the domino
hydroamination–alkyne addition reaction a zinc-cata-
lyzed hydroamination to the corresponding Markovni-
kov product takes place. Subsequently, the resulting
activated electrophilic enamine reacts with a second
alkyne generating a quaternary propargylamine.
After the successful establishment of domino hy-
droamination–alkyne addition reactions, at which an
Scheme 2. Combination of domino hydroamination–alkyne
addition with ring-closing metathesis.
In order to exemplify the applicability of the pre- amine molecule was reacted with two identical alkyne
sented methodology, we decided to combine this units, we were interested in the applicability of two
domino reaction with an enyne ring closing metathe- different alkynes. Such cross-coupling reactions re-
sis (RCM).[16] For this purpose, N-benzylbut-3-enyl- quire different reaction rates of the alkyne derivatives
ACHTUNGTRENNUNGamine was reacted with 2 equivalents of 1-octyne and in the individual reaction steps. As intramolecular hy-
1 mol% catalyst at 808C (Scheme 2). After 24 h the droamination of alkynes to six-membered heterocy-
reaction was completed and the enyne 12 was isolated cles compared to bimolecular reactions is considera-
with 77% yield. Since tertiary amines are problematic bly favored, we have studied the combination of the
substrates for Ru-catalyzed metathesis reactions, we ring-closing reaction with the subsequent addition of
performed the RCM in the presence of 1 equivalent a second alkyne. Our initial efforts focused on amino-
Table 2. Domino hydroamination–alkyne addition with two different alkynes.
Entry
Substrate
Cat. loading [mol%]
Temp. [8C]
Time [h]
Yield [%]
Product
9
10
10
1
60
80
3
54
86
76
11
10
60
4
66
12
13
10
10
r.t.
60
12
1
90
90
14
15
10
10
r.t.
60
16
1
91
91
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Zinc-Catalyzed Domino Hydroamination–Alkyne Addition
Scheme 3. Results obtained in the study of the Zn-catalyzed alkyne addition to the hydroamination intermediate.
alkynes, which lead to instable cyclic products and
We propose a domino hydroamination–Michael ad-
which are converted to a stable amine via addition of dition–Mannich reaction process as mechanistic ex-
the second alkyne. In a first experiment a 1/2.5 mix- planation for the formation of 22 (Scheme 4) via en-
ture of amine 14 and phenylacetylene was heated at amine 26 as key intermediate. The presence of both
608C in benzene-d6 with 10 mol% of catalyst. The re- oxygen and nitrogen should favor the formation of
action was completed after 3 h yielding the propargyl- 26, which undergoes Michael addition to the propyno-
amine 15 with 86% after chromatography (Table 2, ic ester and consecutive intramolecular Mannich reac-
entry 9). Next we tested the minimum of catalyst tion. The whole process may also be activated via
loading. With 1 mol% 1 and 2 we obtained 76% prod- Lewis acid catalysis.
uct, however the reaction needed 54 h at 808C. To an-
Since enamine 26 may be a reaction intermediate,
alyze the tolerance of the zinc catalyst towards highly we studied the same reaction for 16, 18 and 20 with-
polar functional groups, we prepared substrates con- out the addition of a second alkyne.
taining para- and ortho-nitro groups. The ortho-nitro
Exclusion of phenylacetylene in the case of sub-
containing substrate 16 led to propargylamine 17 in strate 16 did not result in the formation of any isola-
the presence of phenylacetylene at 608C in moderate ble product. When the reaction with amine 18 was
yield in a short time (Table 2, entry 11). The para- performed in the absence of phenylacetylene, how-
nitro containing substrate 18 was converted to the
corresponding product 19 at room temperature in the
presence of phenylacetylene in 12 h in high yield
(Table 2, entry 12). At 608C the reaction took only
1 h and provided the product 19 also in high yield
(Table 2, entry 13). The ortho-substitued amine 20
gave similar results to furnish the para-analogue
(Table 2, entries 14 and 15).
To gain insight into the substrate scope, phenylace-
tylene was substituted by propynoic esters. To our sur-
prise, when propynoic acid ethyl[17] and methyl esters
were used, bicyclic cyclobutene structures were isolat-
ed (Scheme 3). In this case, the cross-coupling is pos-
sible by doing the hydroamination of 14 first and
adding the propynoic methyl ester after 1 h. The reac-
tion was completed within 6 h at 608C and 22 was iso-
lated as crude material in 60% yield.
Scheme 4. Proposed mechanism of the BDI-zinc-catalyzed
hydroamination–Michael addition–Mannich cascade reac-
tion.
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Mustafa Biyikal et al.
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ACHTUNGTRENNUNG
product (Scheme 3).
Part of this work was supported by the Cluster of Excellence
“Unifying Concepts in Catalysis” coordinated by the Techni-
sche Universitꢀt Berlin and funded by the Deutsche For-
schungsgemeinschaft.
Unlike the para-nitro-containing substrate 18, the
corresponding ortho-nitro-containing analogue 20
showed a domino hydroamination–alkyne addition re-
action even in the absence of phenylacetylene. The
isolated product 24 showed that a second equivalent
of the starting material 20 adds with its alkyne group
to the in situ generated cyclic hydroamination inter-
mediate. Along with obtained product 24, the acyclic
ketone 25 was isolated in low yield. This result is as-
cribed to the neighboring group effect of the ortho-
nitro group that stabilizes the in situ generated cyclic
iminium ion and allows the addition of alkynes
having aliphatic substitution. In the presence of phe-
nylacetylene, 24 and 25 were not observed and the
cyclic product 21 was isolated in 91% yield (Table 2,
entries 14 and 15).
During the preparation of this manuscript one
report on a tandem amination–alkynylation reaction
has been published.13d Hammond and co-workers
report a copper-catalyzed N-heterocycles synthesis
with similar yields as the ones presented in Table 2.
In summary, we have developed a highly efficient
zinc-catalyzed domino hydroamination–alkyne addi-
tion reaction of secondary amines with terminal al-
kynes to furnish quaternary propargylamines with
four different substituents. This method allows the
access to bulky and highly functionalized amines from
economic starting materials in one step. We have also
reported the first Zn-catalyzed amination–Michael–
Mannich cascade reaction to bicyclic cyclobutene de-
rivatives. Further studies on the reaction scope, enan-
tioselective methods, and combination of the method-
ology in novel cascade processes are currently under
investigation in our group.
References
[1] For selected reviews, see: a) S. F. Kirsch, Synthesis
2008, 20, 3183–3204; b) K. C. Nicolaou, T. Montagnon,
S. A. Snyder, Chem. Commun. 2003, 551–564; c) J.-C.
Wasilke, S. J. Obrey, R. T. Baker, G. C. Bazan, Chem.
Rev. 2005, 105, 1001–1020; d) J.-C. Wasilke, S. J. Obrey,
R. T. Baker, G. C. Bazan, Chem. Rev. 2005, 105, 1001–
1020; e) L. F. Tietze, Chem. Rev. 1996, 96, 115–136.
[2] Domino reactions: a) L. F. Tietze, T. Kinzel, C. C.
Brazel, Acc. Chem. Res. 2009, 42, 367–378; b) B. M.
Trost, N. Maulide, R. C. Livingston, J. Am. Chem. Soc.
2008, 130, 16502–16503; c) L. F. Tietze, K. M. Sommer,
J. Zinngrebe, F. Stecker, Angew. Chem. 2005, 117, 262–
264; Angew. Chem. Int. Ed. 2005, 44, 257–259;
d) S. A. A. El Bialy, H. Braun, L. F. Tietze, Angew.
Chem. 2004, 116, 5505–5507; Angew. Chem. Int. Ed.
2004, 43, 5391–5393; e) L. F. Tietze, H. Evers, E.
Tçpken, Angew. Chem. 2001, 113, 927–929; Angew.
Chem. Int. Ed. 2001, 40, 903–905.
[3] Cascade reactions: a) K. C. Nicolaou, T. R. Wu, Q.
Kang, D. Y.-K. Chen, Angew. Chem. 2009, 121, 3492–
3495; Angew. Chem. Int. Ed. 2009, 48, 3440–3443;
b) E. R. Strieter, A. Koglin, Z. D. Aron, C. T. Walsh, J.
Am. Chem. Soc. 2009, 131, 2113–2115; c) S. van Pelt, F.
van Rantwijk, R. A. Sheldon, Adv. Synth. Catal. 2009,
351, 397–404; d) X. Gao, H. Fu, R. Qiao, Y. Jiang, Y.
Zhao, J. Org. Chem. 2008, 73, 6864–6866.
[4] For selected reviews, see: a) T. E. Mꢀller, K. C.
Hultzsch, M. Yus, F. Foubelo, M. Tada, Chem. Rev.
2008, 108, 3795–3892; b) K. C. Hultzsch, Adv. Synth.
Catal. 2005, 347, 367–391; c) P. W. Roesky, T. E.
Mꢀller, Angew. Chem. 2003, 115, 2812–2814; Angew.
Chem. Int. Ed. 2003, 42, 2708–2710; d) J. Seayad, A.
Tillack, C. G. Hartung, M. Beller, Adv. Synth. Catal.
2002, 344, 795–813; e) M. Nobis, B. Drießen-Hçlscher,
Angew. Chem. 2001, 113, 4105–4108; Angew. Chem.
Int. Ed. 2001, 40, 3983–3985; f) T. E. Mꢀller, M. Beller,
Chem. Rev. 1998, 98, 675–703.
[5] a) H. F. Yuen, T. J. Marks, Organometallics 2009, 28,
2423–2440; b) Z. Zhang, S. D. Lee, R. A. Widenhoefer,
J. Am. Chem. Soc. 2009, 131, 5372–5373; c) S. B.
Herzon, J. F. Hartwig, J. Am. Chem. Soc. 2008, 130,
14940–14941; d) M. Rastꢁtter, A. Zulys, P. W. Roesky,
Chem. Eur. J. 2007, 13, 3606–3616; e) H. Kim, Y. K.
Kim, J. H. Shim, M. Kim, M. Han, T. Livinghouse, P. H.
Lee, Adv. Synth. Catal. 2006, 348, 2609–2618; f) A.
Zulys, T. K. Panda, M. T. Gamer, P. W. Roesky, Orga-
nometallics 2005, 24, 2197–2202; g) A. Zulys, T. K.
Panda, M. T. Gamer, P. W. Roesky, Chem. Commun.
2004, 2584–2585; h) Y. K. Kim, T. Livinghouse, Y.
Horino, J. Am. Chem. Soc. 2003, 125, 9560–9561; i) S.
Hong, S. Tian, M. V. Metz, T. J. Marks, J. Am. Chem.
Soc. 2003, 125, 14768–14783; j) S. Hong, T. J. Marks, J.
Experimental Section
General Tandem Hydroamination Procedure
Reactions were typically performed in NMR tubes and pre-
pared in an N2-filled glove-box. The substrate (0.36 mmol)
and the alkyne (0.9 mmol) were dissolved in C6D6 (0.5 mL)
and added to the precatalyst 1 (e.g., 36 mmol for 10 mol%)
and then to the cocatalyst [PhNMe2H]ACTHNUTRGNEUNG[OTf] (36 mmol for 10
mol%). In the case of 1 mol% catalyst loading the amount
of substrates increased to 3.6 mmol. Subsequently, the mix-
ture was injected into an NMR tube, removed from the
glove-box, cooled to À1968C and flame-sealed under
vacuum. The reaction mixture was then heated in an oil
bath for the stated duration of time.
Procedures and analytical data for all compounds are
given in the Supporting Information.
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Adv. Synth. Catal. 2010, 352, 1870 – 1875

Zinc-Catalyzed Domino Hydroamination–Alkyne Addition
Am. Chem. Soc. 2002, 124, 7886–7887; k) M. R. Bꢀrg-
stein, H. Berberich, P. W. Roesky, Chem. Eur. J. 2001,
7, 3078–3085.
[9] a) X. Liu, P. Ding, J. Huang, C. Che, Org. Lett. 2007, 9,
2645–2648; b) C. S. Yi, S. Y. Yun, I. A. Guzei, J. Am.
Chem. Soc. 2005, 127, 5782–5783.
[10] L. D. Field, B. A. Messerle, S. L. Wren, Organometallics
[6] a) J.-W. Pissarek, D. Schlesiger, P. W. Roesky, S. Ble-
chert, Adv. Synth. Catal. 2009, 351, 2081–2085; b) M.
Biyikal, K. Lçhnwitz, P. W. Roesky, S. Blechert, Synlett
2008, 20, 3106–3110; c) M. Dochnahl, K. Lçhnwitz, J.-
W. Pissarek, P. W. Roesky, S. Blechert, Dalton Trans.
2008, 2844–2848; d) M. Dochnahl, K. Lçhnwitz, J.-W.
Pissarek, M. Biyikal, S. R. Schulz, S. Schçn, N. Meyer,
P. W. Roesky, S. Blechert, Chem. Eur. J. 2007, 13, 6654–
6666; e) N. Meyer, K. Lçhnwitz, A. Zulys, P. W.
Roesky, M. Dochnahl, S. Blechert, Organometallics
2006, 25, 3730–3734; f) M. Dochnahl, J.-W. Pissarek, S.
Blechert, K. Lçhnwitz, P. W. Roesky, Chem. Commun.
2006, 3405–3407; g) A. Zulys, M. Dochnahl, D. Holl-
mann, K. Lçhnwitz, J.-S. Herrmann, P. W. Roesky, S.
Blechert, Angew. Chem. 2005, 117, 7972–7976; Angew.
Chem. Int Ed. 2005, 44, 7794–7798.
2003, 22, 4393–4395.
[11] a) Y. Yin, W. Ma, Z. Chai, G. Zhao, J. Org. Chem.
2007, 72, 5731–5736; b) S. Chang, M. Lee, D. Y. Jung,
E. J. Yoo, S. H. Cho, S. K. Han, J. Am. Chem. Soc.
2006, 128, 12366–12367; c) C. S. Yi, S. Y. Yun, J. Am.
Chem. Soc. 2005, 127, 17000–17006.
[12] C. Gardner, V. Kerrigan, J. D. Rose, B. C. L. Weedon,
J. Chem. Soc. 1949, 780–782.
[13] a) L. Zhou, D. S. Bohle, H.-F. Jiang, C.-J. Li, Synlett
2009, 6, 937–940; b) L. Zhou, Q. Shuai, H.-F. Jiang, C.-
J. Li, Chem. Eur. J. 2009, 15, 11668–11674; c) L. Zhou,
H.-F. Jiang, C.-J. Li, Adv. Synth. Catal. 2008, 350, 2226–
2230; d) J. Han, B. Xu, G. B. Hammond, J. Am. Chem.
Soc. 2010, 132, 916–917.
[14] C. W. Kruse, R. F. Kleinschmidt, J. Am. Chem. Soc.
1961, 83, 216–220.
[7] a) K. Alex, A. Tillack, N. Schwarz, M. Beller, Chem-
[15] a) L. Zani, S. Alesi, P. G. Cozzi, C. Bolm, J. Org. Chem.
2006, 71, 1558–1562; b) K. Y. Lee, C. G. Lee, J. E. Na,
J. N. Kim, Tetrahedron Lett. 2005, 46, 69–74; c) C.
Fischer, E. M. Carreira, Org. Lett. 2004, 6, 1497–1499;
d) B. Jiang, Y.-G. Si, Tetrahedron Lett. 2003, 44, 6767–
6768; e) J. F. Traverse, A. H. Hoveyda, M. L. Snapper,
Org. Lett. 2003, 5, 3273–3275.
[16] a) Y.-J. Lee, R. R. Schrock, A. H. Hoveyda, J. Am.
Chem. Soc. 2009, 131, 10652–10661; b) A. Niethe, D.
Fischer, S. Blechert, J. Org. Chem. 2008, 73, 3088–
3093; c) A. R. Katritzky, S. K. Nair, T. Khokhlova,
N. G. Akhmedov, J. Org. Chem. 2003, 68, 5724–5727;
d) M. Mori, N. Sakakibara, A. Kinoshita, J. Org. Chem.
1998, 63, 6082–6083; e) M. Schuster, S. Blechert,
Angew. Chem. 1997, 109, 2124–2144; Angew. Chem.
Int. Ed. Engl. 1997, 36, 2036–2056.
ACHTUNGTRENNUNGSusChem 2008, 1, 333–338; b) M. L. Buil, M. A. Ester-
uelas, A. M. Lꢄpez, A. C. Mateo, E. OÇate, Organome-
tallics 2007, 26, 554–565; c) A. Tillack, V. Khedkar, H.
Jiao, M. Beller, Eur. J. Org. Chem. 2005, 5001–5012;
d) A. Tillack, H. Jiao, I. G. Castro, C. G. Hartung, M.
Beller, Chem. Eur. J. 2004, 10, 2409–2420; e) C. Li,
R. K. Thomson, B. Gillon, B. O. Patrick, L. L. Schafer,
Chem. Commun. 2003, 2462–2463; f) A. Tillack, I. G.
Castro, C. G. Hartung, M. Beller, Angew. Chem. 2002,
114, 2646–2648; Angew. Chem. Int. Ed. 2002, 41, 2541–
2543; g) C. G. Hartung, A. Tillack, H. Trauthwein, M.
Beller, J. Org. Chem. 2001, 66, 6339–6343.
[8] J. Bourgeois, I. Dion, P. H. Cebrowski, F. Loiseau, A.-
C. Bꢅdard, A. M. Beauchemin, J. Am. Chem. Soc. 2009,
131, 874–875.
[17] For analytical data see Supporting Information.
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