Silver(I)-mediated dual cleavage of C-C and C-O bonds in the reaction of diarylmethylenecyclopropanes with tetrahydrofuran: Synthesis of 4-(3-halobut-3-enyloxy)butyl 2,2,2-trifluoroacetate derivatives

Article abstract of DOI:10.1002/ejoc.201301262

The reaction of methylenecyclopropanes (MCPs) with tetrahydrofuran (THF) proceed smoothly in the presence of AgOC(O)CF₃ and electrophilic halogenation reagents to give the corresponding 4-(3-halobut-3-enyloxy)butyl 2,2,2-trifluoroacetate derivatives in moderate yields through dual cleavage of C-C and C-O bonds under mild conditions. Novel 4-(3-halobut-3-enyloxy)butyl 2,2,2-trifluoroacetate derivatives can be synthesized by Ag^I-mediated reactions of arylmethylenecyclopropanes with tetrahydrofuran at room temperature through dual cleavage of C-C and C-O bonds. Copyright

Full text of DOI:10.1002/ejoc.201301262

FULL PAPER
DOI: 10.1002/ejoc.201301262
Silver(I)-Mediated Dual Cleavage of C–C and C–O Bonds in the Reaction of
Diarylmethylenecyclopropanes with Tetrahydrofuran: Synthesis of
4-(3-Halobut-3-enyloxy)butyl 2,2,2-Trifluoroacetate Derivatives
Gen-Qiang Chen,[a] Xiang-Ying Tang,*[a] and Min Shi*[a]
Keywords: Silver / C–C activation / Small ring systems / Alkenes / Halogenation / Oxidation
The reaction of methylenecyclopropanes (MCPs) with tetra- the corresponding 4-(3-halobut-3-enyloxy)butyl 2,2,2-tri-
hydrofuran (THF) proceed smoothly in the presence of
AgOC(O)CF3 and electrophilic halogenation reagents to give
fluoroacetate derivatives in moderate yields through dual
cleavage of C–C and C–O bonds under mild conditions.
solvent in the presence of AgOC(O)CF3, compound 2a was
formed rather than the desired decarboxylated and tri-
fluoromethylated product. Apparently, one molecule of
THF was incorporated into the final product. Herein, we
report this novel AgI-mediated reaction of arylmethylenecy-
clopropanes with THF, which proceeds through dual cleav-
age of C–C and C–O bonds.
Introduction
Methylenecyclopropanes (MCPs) are versatile building
blocks in organic synthesis.[1] The direct connection of a
double bond to the cyclopropane functionality endows this
molecule with extra strain and reactivity.[2] MCPs undergo
a variety of ring-expansion/ring-opening/cycloaddition re-
actions in the presence of transition metals or Lewis acids
because the relief of ring strain can provide a powerful
thermodynamic driving force.[3–5] In 2003 and 2004, our
group reported ring-opening reactions of MCPs promoted
by metal halides (Lewis acids) in which homoallylic halides
could be obtained in high yields (Scheme 1).[6]
Results and Discussion
We examined in detail the reaction conditions for AgI-
mediated reaction of diarylmethylenecyclopropanes with
THF and the results are indicated in Table 1. Using NIS
(2 equiv.) and AgOC(O)CF3 (2 equiv.) as the reagents,
product 2a was afforded in 62% yield at room temperature
(Table 1, entry 1). The yield of 2a decreased to 39 and 45%
when the ratios of NIS/AgOC(O)CF3 were 2:1 (entry 2) and
3:1 (entry 3), respectively. The influence of temperature on
the reaction was also examined. When the reaction was
conducted at 40 °C, the yield of 2a was 65% (entry 4). Rais-
ing the reaction temperature to 60 °C afforded 2a in 60%
yield (entry 5). Complex product mixtures were obtained
when the reaction was performed at –2 °C (entry 6).
With the optimized conditions in hand, we evaluated the
generality of the reaction. A range of substrates with vary-
ing substituents were synthesized and investigated under the
standard conditions. As can be seen from Table 2, for di-
arylmethylenecyclopropanes with electron-donating substit-
uents, the reaction proceeded smoothly to give the desired
products 2b–e in higher yields (entries 1–4). When R1 and
R2 had electron-withdrawing halogen atoms, the desired
products 2f and 2g were obtained in lower yields (entries 5
and 6). Only trace amounts of product were afforded when
R1 and R2 had strongly electron-withdrawing fluorine or
trifluoromethyl groups, presumably due to the electronic ef-
fect in these two cases (entries 7 and 8).
Scheme 1. Our previous work and this work.
During our studies on the trifluoromethylation of
MCPs,[7,8] we attempted to use AgOC(O)CF3 as an alterna-
tive source of the CF3 group. Interestingly, we found that
conducting the reaction of MCP 1a using N-iodosuccin-
imide (NIS) as oxidant and tetrahydrofuran (THF) as
[a] State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences,
345 Lingling Road, Shanghai 200032, China
E-mail: Mshi@mail.sioc.ac.cn
www.sioc.ac.cn
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201301262.
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© 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Methylenecyclopropanes as Versatile Building Blocks
Table 1. Optimization of the reaction conditions.
Table 3. Substrate scope of AgOC(O)CF3 and NBS-mediated reac-
tion of MCPs with THF.
Entry[a]
NIS/AgOC(O)CF3
(equiv./equiv.)
T [°C]
Yield [%][b]
Entry[a]
1
R1, R2
3
Yield [%][b]
1
2
3
4
5
6
7
8
9
1a
1b
1c
1d
1e
1f
1g
1h
1i
R1 = R2 = Ph
3a
3b
3c
3d
3e
3f
3g
3h
3i
46
53
45
1
2
3
4
5
6
2:2
2:1
3:1
2:2
2:2
2:2
room temp.
room temp.
room temp.
62
39
45
65
60
R1 = R2 = p-MeC6H4
R1 = R2 = m-MeC6H4
R1 = Ph, R2 = o-MeC6H4
R1 = R2 = p-MeOC6H4
R1 = R2 = p-ClC6H4
R1 = R2 = p-BrC6H4
R1 = R2 = p-FC6H4
R1 = R2 = p-CF3C6H4
44[c]
trace
41
40
60
–2
complex
37
37
28
[a] The reaction was performed in a 25 mL flame- and vacuum-
dried Schlenk tube. Compound 1a (41 mg, 0.2 mmol), NIS (88 mg,
0.4 mmol) and AgOC(O)CF3 (90 mg, 0.4 mmol) were added, the
tube was evacuated and backfilled with Ar, then the solvent was
added and the reaction mixture was stirred at the indicated tem-
perature for 12 h. [b] Isolated yield.
[a] The reaction was performed in a 25 mL flame- and vacuum-
dried Schlenk tube. Compound (0.2 mmol), NBS (71 mg,
0.4 mmol) and AgOC(O)CF3 (90 mg, 0.4 mmol) were added, the
tube was evacuated and backfilled with Ar, then THF (2 mL) was
added and the reaction mixture was stirred at room temperature
for 12 h. [b] Isolated yield. [c] The product was obtained as an
Z/E mixture (ratio 1.12:1).
1
Table 2. Substrate scope of AgOC(O)CF3 and NIS-mediated reac-
tion of MCPs with THF.
Table 4. AgOC(O)CF3 and I2-mediated reaction of MCPs with
THF.
Entry[a]
1
R1, R2
2
Yield [%][b]
1
2
3
4
5
6
7
8
1b
1c
1d
1e
1f
1g
1h
1i
R1 = R2 = p-MeC6H4
R1 = R2 = m-MeC6H4
R1 = Ph, R2 = o-MeC6H4
R1 = R2 = p-MeOC6H4
R1 = R2 = p-ClC6H4
R1 = R2 = p-BrC6H4
R1 = R2 = p-FC6H4
2b
2c
2d
2e
2f
2g
2h
2i
74
71
Entry[a]
1
R1, R2
2
Yield [%][b]
62[c]
66
1
2
3
4
1a
1b
1e
1g
R1 = R2 = Ph
R1 = R2 = p-MeC6H4
R1 = Ph, R2 = p-MeOC6H4
R1 = R2 = p-BrC6H4
2a
2b
2e
2g
50
61
54
46
54
53
trace
trace
R1 = R2 = p-CF3C6H4
[a] The reaction was performed in a 25 mL flame- and vacuum-
dried Schlenk tube. Compound 1 (0.2 mmol) and AgOC(O)CF3
(90 mg, 0.2 mmol) were added, the tube was evacuated and back-
filled with Ar, then THF (1 mL) was added and I2 (101 mg,
0.4 mmol) solution in THF (1 mL) was added dropwise. [b] Isolated
yield.
[a] The reaction was performed in a 25 mL flame- and vacuum-
dried Schlenk tube. Compound (0.2 mmol), NIS (88 mg,
0.4 mmol) and AgOC(O)CF3 (90 mg, 0.4 mmol) were added, the
tube was evacuated and backfilled with Ar, then THF was added
and the reaction mixture was stirred at room temp. for 12 h. [b] Iso-
lated yield. [c] The product was obtained as an Z/E mixture (ratio
1.56:1).
1
A plausible reaction mechanism is shown in Scheme 2
with 1a as a model substrate. Compound 1a first reacts with
Other halogenating reagents such as N-bromosuccin- NIS to afford halonium intermediate A. This intermediate
imide (NBS), N-chlorosuccinimide (NCS) and iodine were can be attacked either by the halide to form 4 (path a) or
also examined. NCS was found to be ineffective in this reac- by THF to form intermediate B (path b). After halogen ab-
tion. Upon using NBS to replace NIS, the corresponding straction by AgI and subsequent nucleophilic attack by the
brominated products 3 were obtained albeit in lower yield oxygen atom of THF, cationic intermediate B can also be
than with NIS (Table 3). In the case of MCP 1e, only a formed from compound 4.[9] The final product 2a or 3a can
trace amount of product was produced (entry 5), whereas, be formed after nucleophilic ring-opening of intermediate
the use of MCP 1h or 1i as substrate afforded the desired A by trifluoroacetate.[10] Strain release of MCPs and the
product 3h and 3i in 37 and 28% yield, respectively (en- precipitation of silver halide would be the driving forces of
tries 8 and 9). By using iodine to replace NIS, the desired this novel process.
products 2 could also be produced in moderate yields, and
selected examples are given in Table 4.
To verify the reaction pathway, we attempted to identify
or isolate the possible reaction intermediate in this reaction.
Other cyclic ethers such as 2-Me-THF, 1,4-dioxane, Key intermediate 4 could be isolated in AgOC(O)CF3 and
tetrahydropyran, oxane, and oxetane were also examined I2 mediated reaction of MCPs with THF (Table 4). We
under the standard conditions, but no desired product was found that when compound 4 (synthesized through a
observed (see Table S1 in the Supporting Information).
known route[9]) or 2-phenylethyl bromide were used in the
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195

G.-Q. Chen, X.-Y. Tang, M. Shi
FULL PAPER
THF under the standard conditions, exclusively giving ha-
logenated products 2 and 3.
Scheme 4. AgOAc-mediated reaction of MCP 1a with THF.
Conclusion
Scheme 2. Proposed reaction mechanism.
We have developed a novel silver(I)-mediated reaction of
diarylmethylenecyclopropanes with THF and halogenation
reagents, affording the corresponding 4-(3-halobut-3-en-
yloxy)butyl 2,2,2-trifluoroacetate derivatives in moderate
yields under mild conditions. A plausible reaction mecha-
nism has also been proposed. Efforts are in progress to in-
vestigate further the mechanistic details of this novel meth-
odology.
absence of NIS or NBS, the expected products 2a and 5
were indeed afforded in 65 and 61% yield, respectively, indi-
cating that 4 was probably the reaction intermediate of this
reaction (Scheme 3). This may therefore be a more general
reaction for introducing a trifluoroacetylbutanediol unit
with many haloalkanes. Without the addition of AgOC(O)-
CF3, the reaction was sluggish, affording 4 in only 18%
yield after 12 h and 54% yield after 36 h, along with other
unidentified byproducts. Use of alkene 6 as substrate led to
complex product mixtures under the standard conditions,
indicating that this reaction is not suitable for other alkenes.
Experimental Section
AgOC(O)CF3 and NXS (X = I, Br) Mediated Reactions of Diaryl-
methylenecyclopropanes with THF. General Procedure: To a 25 mL
flame- and vacuum-dried Schlenk tube were added 1 (0.2 mmol),
NIS (88 mg, 0.4 mmol) and AgOC(O)CF3 (90 mg, 0.4 mmol). The
tube was evacuated and backfilled with Ar, then THF was added
and the reaction mixture was stirred at the indicated temperature
for 12 h. The product was purified by flash column chromatog-
raphy (petroleum ether/ethyl acetate, 40:1).
AgOC(O)CF3 and I2 Mediated Reactions of Diarylmethylenecyclo-
propanes with THF. General Procedure: To a 25 mL flame- and vac-
uum-dried Schlenk tube were added 1 (0.2 mmol) and AgOC(O)-
CF3 (90 mg, 0.4 mmol). The tube was evacuated and backfilled
with Ar, then THF (1.0 mL) was added and I2 (101 mg, 0.4 mmol)
dissolved in THF (1 mL) was added dropwise. When the addition
was complete, the white precipitate was filtered off and the reaction
was quenched with saturated sodium thiosulfate. The product was
purified by flash column chromatography (petroleum ether/ethyl
acetate, 40:1).
4-(3-Iodo-4,4-diphenylbut-3-enyloxy)butyl
2,2,2-Trifluoroacetate
(2a): Yield 65 mg (62%); colorless oil. 1H NMR (400 MHz, CDCl3,
TMS): δ = 1.64–1.69 (m, 2 H, CH2), 1.83–1.87 (m, 2 H, CH2), 2.82
(t, J = 6.4 Hz, 2 H, CH2), 3.43 (t, J = 6.4 Hz, 2 H, CH2), 3.65 (t,
J = 6.4 Hz, 2 H, CH2), 4.38 (t, J = 6.4 Hz, 2 H, CH2), 7.19–7.33
(m, 10 H, Ar) ppm. 13C NMR (100 MHz, CDCl3, TMS): δ = 25.2,
25.8, 41.9, 68.1, 69.9, 70.2, 104.6, 114.5 (q, J = 283.7 Hz), 127.26,
127.28, 128.2, 128.3, 128.62, 128.63, 140.1, 146.8, 150.0, 157.5 (q,
J = 41.9 Hz) ppm. 19F NMR (376 MHz, CDCl3, CFCl3): δ =
Scheme 3. Control experiments.
Moreover, when AgOAc was used in this reaction instead
of AgOC(O)CF3 under the standard conditions, complex
product mixtures were produced with no desired product
(Scheme 4). It has to be mentioned that THF can undergo
cationic ring-opening polymerization (CROP) when there
are no other strong nucleophiles.[11] As can be seen from
the pKa values shown in Scheme 4, acetate is more nucleo-
philic than trifluoroacetate and trifluoroacetate is more nu-
cleophilic than THF. Therefore, the more nucleophilic acet-
ate may compete with the formation of intermediate A, thus
making the reaction system more complex (Scheme 4). The
weak nucleophilic trifluoroacetate can favor the formation
–75.1 ppm. IR (CH Cl ): ν = 2939, 2862, 1783, 1491, 1350, 1219,
˜
2
2
1155, 730, 698 cm–1. MS (ESI): m/z = 536.1 [M+ + NH4]. HRMS
(ESI): calcd. for C22H26F3INO3 [M+ + NH4] 536.0909; found
536.0903.
4-(3-Bromo-4,4-diphenylbut-3-enyloxy)butyl 2,2,2-Trifluoroacetate
(3a): Yield 43 mg (46%); colorless oil. 1H NMR (400 MHz, CDCl3,
TMS): δ = 1.65–1.68 (m, 2 H, CH2), 1.83–1.87 (m, 2 H, CH2), 2.83
of intermediate A and also effectively prohibit CROP of (t, J = 6.4 Hz, 2 H, CH2), 3.44 (t, J = 6.0 Hz, 2 H, CH2), 3.70 (t,
196
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Methylenecyclopropanes as Versatile Building Blocks
2006, 8, 835; h) M. Lautens, C. Meyer, A. Lorenz, J. Am.
Chem. Soc. 1996, 118, 10676.
J = 6.4 Hz, 2 H, CH2), 4.38 (t, J = 6.4 Hz, 2 H, CH2), 7.23–7.33
(m, 10 H, Ar) ppm. 13C NMR (100 MHz, CDCl3, TMS): δ = 25.2,
25.8, 38.7, 68.1, 68.9, 69.9, 114.5 (q, J = 283.6 Hz), 123.7, 127.2,
127.3, 128.0, 128.3, 128.9, 129.0, 140.6, 143.2, 143.7, 157.5 (q, J =
[5] For cycloadditions involving MCPs, see: a) L.-X. Shao, B. Xu,
J.-W. Huang, M. Shi, Chem. Eur. J. 2006, 12, 510; b) K. Gao,
Y. Li, H. Sun, R. Fan, J. Wu, Synth. Commun. 2007, 37, 4425;
c) M. E. Scott, M. Lautens, Org. Lett. 2005, 7, 3045; d) I. Nak-
amura, B. H. Oh, S. Saito, Y. Yamamoto, Angew. Chem. 2001,
113, 1338; Angew. Chem. Int. Ed. 2001, 40, 1298; e) K. Chen,
Z. Zhang, Y. Wei, M. Shi, Chem. Commun. 2012, 48, 7696; f)
C. Taillier, M. Lautens, Org. Lett. 2007, 9, 591; g) T. Kurahashi,
A. de Meijere, Angew. Chem. 2005, 117, 8093; Angew. Chem.
Int. Ed. 2005, 44, 7881.
45.2 Hz) ppm. 19F NMR (376 MHz, CDCl3, CFCl3):
δ =
–75.1 ppm. IR (CH Cl ): ν = 2927, 2862, 1784, 1350, 1220, 1156,
˜
2
2
1116, 732, 700 cm–1. MS (ESI): m/z = 488.1 [M+ + NH4]. HRMS
(ESI): calcd. for C22H25BrF3NO3 [M+ + NH4] 488.1048; found
488.1042.
Supporting Information (see footnote on the first page of this arti-
cle): Spectroscopic data of compounds shown in Tables and
Schemes and the detailed descriptions of the experimental pro-
cedures.
[6] a) B. Xu, M. Shi, Org. Lett. 2003, 5, 1415; b) J.-W. Huang, M.
Shi, Tetrahedron 2004, 60, 2057.
[7] For reviews on trifluoromethylation, see: a) M. Schlosser, An-
gew. Chem. 2006, 118, 5558; Angew. Chem. Int. Ed. 2006, 45,
5432; b) J.-A. Ma, D. Cahard, J. Fluorine Chem. 2007, 128,
975; c) J.-A. Ma, D. Cahard, Chem. Rev. 2008, 108, PR1; d)
O. A. Tomashenko, V. V. Grushin, Chem. Rev. 2011, 111, 4475.
[8] For selected recent examples of trifluoromethylation, see: a) I.
Nowak, M. J. Robins, J. Org. Chem. 2007, 72, 2678; b) M.
Oishi, H. Kondo, H. Amii, Chem. Commun. 2009, 1909; c)
G. G. Dubinina, H. Furutachi, D. A. Vicic, J. Am. Chem. Soc.
2008, 130, 8600; d) H. Kawai, T. Furukawa, Y. Nomura, E.
Tokunaga, N. Shibata, Org. Lett. 2011, 13, 3596; e) C.-P.
Zhang, Z.-L. Wang, Q.-Y. Chen, C.-T. Zhang, Y.-C. Gu, J.-C.
Xiao, Angew. Chem. 2011, 123, 1936; Angew. Chem. Int. Ed.
2011, 50, 1896; f) O. A. Tomashenko, E. C. Escudero-Adan,
M. M. Belmonte, V. V. Grushin, Angew. Chem. 2011, 123, 7797;
Angew. Chem. Int. Ed. 2011, 50, 7655; g) H. Morimoto, T. Tsu-
bogo, N. D. Litvinas, J. F. Hartwig, Angew. Chem. 2011, 123,
3877; Angew. Chem. Int. Ed. 2011, 50, 3793; h) T. Knauber, F.
Arikan, G.-V. Röoschenthaler, L. J. Gooßen, Chem. Eur. J.
2011, 17, 2689; i) G. G. Dubinina, J. Ogikubo, D. A. Vicic, Or-
ganometallics 2008, 27, 6233.
Acknowledgments
The authors thank the Shanghai Municipal Committee of Science
and Technology (11JC1402600), National Basic Research Program
of China (973)-2009CB825300, and the National Natural Science
Foundation of China (NSFC) for financial support (21072206,
20472096, 21102166, 21372241, 21302203, 20672127, 21121062,
and 20732008).
[1] For reviews on MCPs, see: a) I. Nakamura, Y. Yamamoto, Adv.
Synth. Catal. 2002, 344, 111; b) A. Brandi, S. Cicchi, F. M.
Cordero, A. Goti, Chem. Rev. 2003, 103, 1213; c) M. Rubin,
M. Rubina, V. Gevorgyan, Chem. Rev. 2007, 107, 3117; d) L.-
X. Shao, M. Shi, Curr. Org. Chem. 2007, 11, 1135; e) L. Yu,
R. Guo, Org. Prep. Proced. Int. 2011, 43, 209; f) M. Shi, J.-M.
Lu, Y. Wei, L.-X. Shao, Acc. Chem. Res. 2012, 45, 641.
[2] a) E. Vogel, Angew. Chem. 1960, 72, 4; b) A. G. Samuelson,
Proc. Indian Acad. Sci. Chem. Sci. 1984, 93, 729.
[3] For examples of ring expansion of MCPs, see: a) S. Ma, L. Lu,
J. Zhang, J. Am. Chem. Soc. 2004, 126, 9645; b) M. Lautens,
W. Han, J. H.-C. Liu, J. Am. Chem. Soc. 2003, 125, 4028; c) A.
Fürstner, C. Aïssa, J. Am. Chem. Soc. 2006, 128, 6306; d) M.
Shi, L.-P. Liu, J. Tang, J. Am. Chem. Soc. 2006, 128, 7430; e)
S. G. Sethofer, S. T. Staben, O. Y. Hung, F. D. Toste, Org. Lett.
2008, 10, 4315; f) M. E. Scott, Y. Bathuel, M. Lautens, J. Am.
Chem. Soc. 2007, 129, 1482.
[4] For ring-opening reactions of MCPs, see: a) K. Ogata, D. Shi-
mada, S. Furuya, S. Fukuzawa, Org. Lett. 2013, 15, 1182; b)
L.-X. Shao, J. Li, B.-Y. Wang, M. Shi, Eur. J. Org. Chem. 2010,
6448; c) S. Li, Y. Luo, J. Wu, Org. Lett. 2011, 13, 3190; d) L.-
P. Liu, M. Shi, Chem. Commun. 2004, 2878; e) S. Simaan, I.
Marek, J. Am. Chem. Soc. 2010, 132, 4066; f) M. Shi, L.-X.
Shao, Synlett 2004, 5, 807; g) L. Lu, G. Chen, S. Ma, Org. Lett.
[9] Compound 4 is a known compound, and it was synthesized
according to the reported procedure, see: a) B. Xu, M. Shi,
Org. Lett. 2003, 5, 1415; b) L.-X. Shao, L.-J. Zhao, M. Shi,
Eur. J. Org. Chem. 2004, 4894.
[10] For reactions in which THF was opened in this way, see: a)
G. B. M. Kostermans, M. Bobeldijk, W. H. de Wolf, F. Bickel-
haupt, J. Am. Chem. Soc. 1987, 109, 2471; b) H. C. Lo, H.
Han, L. J. D’Souza, S. C. Sinha, E. Keinan, J. Am. Chem. Soc.
2007, 129, 1246; c) M. A. Wuonola, W. Sheppard, J. Org.
Chem. 1971, 36, 3640; d) A. Oku, K. Kimura, S. Ohwaki, Acta
Chem. Scand. 1993, 47, 391; e) R. W. Van De Water, C.
Hoarau, T. R. R. Pettus, Tetrahedron Lett. 2003, 44, 5109.
[11] a) Y. Li, B. Yu, Chem. Commun. 2010, 46, 6060; b) L. M.
van Renterghem, E. J. Goethals, F. E. du Prez, Macromolecules
2006, 39, 528; c) S. Theiler, T. Hovetborn, H. Keul, M. Moller,
Macromol. Chem. Phys. 2009, 210, 614.
Received: August 22, 2013
Published Online: November 22, 2013
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