Novel [2]rotaxanes based on the recognition of pillar[5]arenes to an alkane functionalized with triazole moieties

Article abstract of DOI:10.1016/j.tet.2012.09.018

Host-guest complexation between an alkane functionalized with triazole moieties and three pillar[5]arenes was studied. Three pillar[5]arene-based [2]rotaxanes were constructed based on this new recognition motif. The sequence of the yields of these [2]rot

Full text of DOI:10.1016/j.tet.2012.09.018

Tetrahedron 68 (2012) 9179e9185
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Novel [2]rotaxanes based on the recognition of pillar[5]arenes to an alkane
functionalized with triazole moieties
*
Peifa Wei, Xuzhou Yan, Jinying Li, Yingjie Ma, Yong Yao, Feihe Huang
Department of Chemistry, Zhejiang University, Hangzhou 310027, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 26 June 2012
Received in revised form 24 August 2012
Accepted 4 September 2012
Available online 10 September 2012
Hosteguest complexation between an alkane functionalized with triazole moieties and three pillar[5]
arenes was studied. Three pillar[5]arene-based [2]rotaxanes were constructed based on this new rec-
ognition motif. The sequence of the yields of these [2]rotaxanes was consistent with the order of as-
sociation constants between the three corresponding pillar[5]arenes and the alkane. 1H NMR,
electrospray ionization mass spectrometry, and NOESY NMR were employed to characterize these [2]
rotaxanes.
Keywords:
Supermolecular chemistry
Self-assembly
Ó 2012 Elsevier Ltd. All rights reserved.
Rotaxanes
Pillararenes
Hosteguest systems
1. Introduction
are composed of five hydroquinone rings linked mutually through
their para positions by methylene bridges. The pillar structure with
One of the most exciting and potentially rewarding challenges
chemists face today is to devise and realize wholly synthetic su-
pramolecular self-assemblies that function like their biological
counterparts.1 Threaded structures2 have attracted great attention
in the development of supramolecular self-assemblies due to their
wide application in the fabrication of molecular machines,3 su-
pramolecular polymers,4 and other functional supramolecular
systems. Rotaxanes, as the basic threaded structures, in which
macrocyclic components encircle linear components and are trap-
ped by bulky stoppers, have been a topic of great interest.5 In order
to prepare these threaded structures and advanced supramolecular
architectures efficiently, it is necessary to increase the association
strengths between the ‘wheel’ and ‘axle’ components. This is one of
the most important reasons to develop more efficient recognition
motifs in hosteguest chemistry.6 Therefore, the incorporation of
new binding sites that can introduce additional weak noncovalent
a p-electron rich cavity renders them superior to calixarenes in the
construction of pseudorotaxanes and rotaxanes.11 However, up to
now, mechanically interlocked threaded structures based on the
recognition of pillar[5]arenes to guest molecules, especially the
basic rotaxane structures, have been rarely explored, although the
hosteguest chemistry of pillar[5]arenes has been actively studied
in the last four years.10 Recently, one example was reported by
Stoddart et al. It was synthesized by complexation between 1,4-
dimethoxypillar[5]arene (DMP5) and 1,8-diaminooctane and then
using 3,5-di-tert-butylbenzaldehyde as stoppers.11d Since CeH/
p
interactions are the main driving forces in this preparation, only
very low yield of the rotaxane (7%) was obtained. Therefore, it is
necessary to introduce new recognition motifs.
The Huisgen-type copper(I)-catalyzed 1,3-dipolar azideealkyne
cycloaddition (CuAAC) has emerged as a valuable tool to fabricate
complex functional materials not only because of its high efficiency
and mild reaction conditions but also due to its function of in-
troducing a new binding site,1,2,3-triazole.12 The triazole appended
with nitrogen atom is expected to contribute more hydrogen-
bonding interactions, which are favorable for the formation of
rotaxanes. For these reasons, a neutral alkyl chain carrying two
azides was used to react with suitable alkynes by means of CuAAC to
get 9 as a model compound (Scheme 1). We then screened the in-
teractions of this model compound with DMP[5], 1,4-diethoxypillar
[5]arene (DEP[5]), and 1,4-bis(n-butoxy)pillar[5]arene (DBP[5]),
which resulted in the formation of interpenetrated complexes.
forces, such as hydrogen bonding,
pep stacking, and electrostatic
interactions between the host and guest definitely plays a prom-
inent role in the efficient preparation of threaded structures.
A variety of macrocycles, such as crown ethers,7 cyclodextrins,8
and cucurbiturils,9 etc. have been widely used in the construction of
threaded structures. Pillar[5]arenes,10 new calixarene analogues,
* Corresponding author. Tel./fax: þ86 571 87953189; e-mail address: fhuang@
zju.edu.cn (F. Huang).
0040-4020/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2012.09.018

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2. Results and discussion
2.1. Syntheses of pillar[5]arene-based [2]rotaxanes
Intermediates 4,13a 5,13b 813b and three pillar[5]arenes (DMP
[5]10a/DEP[5]10g/DBP[5]10g) were synthesized according to litera-
ture procedures. As outlined in Scheme 1, treatment of 5 with 1,5-
diazidopentane in the presence of CuSO4$5H2O and sodium
ascorbate by means of the Huisgen-type copper(I)-catalyzed 1,3-
dipolar azideealkyne cycloaddition (CuAAC) afforded the
bistriazole-containing intermediate 6 in 60% isolated yield. Using
the same method, model compound 9 was also obtained. Treat-
ment of 8 with 1,5-diazidopentane afforded 9 in good yield. The
‘axle’ 7 was prepared via the esterification reaction of easily avail-
able 3,5-dinitrobenzoyl chloride with 6. Rotaxanes 10, 11, and 12
were obtained in reasonable yields in two steps. Intermediate 6 and
pillar[5]arene 1 were firstly mixed for 2 h in chloroform followed by
esterification with 3,5-dinitrobenzoyl chloride as stoppers, and fi-
nally [2]rotaxane 10 was obtained in 23% isolated yield. The other
two [2]rotaxanes 11 and 12 were synthesized in the same way
using DEP[5] and DBP[5] as ‘wheels’ with 27% and 16% yields,
respectively.
Reagents and conditions: (a) 3-bromo-1-propyne, K2CO3, N2, CH3CN,
80 °C, 24 h, 95% for both 4 and 8; (b) NaBH4, MeOH/CH2Cl2 (1:1), 71%;
(c) 1,5-diazidopentane, CuSO4•5H2O, sodium ascorbate, DMF, H2O, 60%
for 6 and 40% for 9; (d) 3,5-dinitrobenzoyl chloride, Et3N, N2, CHCl3,
2.2. Complexation of model compound 9 with pillar[5]arenes
60%; (e) i) DMP[5]/DEP[5]/DBP[5], CHCl3,
3,5-dinitrobenzoyl chloride, Et3N, N2, 23% for 10, 27% for 11 and 16% for
12 (two steps).
2
hours; ii)
Fig. 2 shows the 1H NMR spectra of DMP[5] 1, DEP[5] 2 and DBP
[5] 3 in CDCl3 recorded in the absence and in the presence of
1.0 equiv of model compound 9. The 1H NMR spectrum of an
equimolar solution of host 1 and guest 9 shows three sets of res-
onances for uncomplexed host 1, uncomplexed guest 9, and the
complex between host 1 and guest 9 (Fig. 2, spectra aec), indicating
a typical slow exchange complexation on the proton NMR time
scale. Methylene protons H9e, H9f, and H9g of 9 shifted upfield
from 4.34 ppm, 1.97 ppm, and 1.34 ppm to 2.89 ppm, ꢀ0.77 ppm,
and ꢀ2.08 ppm, respectively (Fig. 2, spectra b and c). However, no
Scheme 1. Syntheses of model compound
9 and three pillar[5]arene-based [2]
rotaxanes.
Subsequently, we designed and prepared three [2]rotaxanes based
on this new recognition motif.1H NMR, electrospray ionization mass
spectrometry, and NOESY NMR results provided converging evi-
dences of the formation of these [2]rotaxanes (Fig. 1).
Fig. 1. Compounds used in this study and their cartoon representation.

P. Wei et al. / Tetrahedron 68 (2012) 9179e9185
9181
1
Fig. 2. H NMR spectra (400 MHz, CDCl3, 20 ꢃC): (a) 1 (10.0 mM); (b) equimolar mixture of 1 (10.0 mM) and 9 (10.0 mM); (c) 9 (10.0 mM); (d) equimolar mixture of 2 (10.0 mM) and
0
9 (10.0 mM); (e) 2 (10.0 mM); (f) equimolar mixture of 3 (10.0 mM) and 9 (10.0 mM); (f) 3 (10.0 mM). The prime in spectrum f denotes complexed species.
obvious changes were observed for protons H9a, H9b, H9c, and H9d
The complexation-induced upfield shifts of the methylene protons
9eeH9g reveal that the host engulfs the central part of the guest,
.
H
which thus leads to an efficient shield toward these guest protons.
On the other hand, complexation-induced chemical shift changes
are small for protons of 1 (Fig. 2, spectra a and b) since only two
aromatic triazole groups of guest 9 are close to 1. The proton NMR
spectra of equimolar (10.0 mM) chloroform-d solutions of the same
guest
9 with 2 and 3 were also investigated and similar
complexation-induced chemical shift changes were observed
(Fig. 2, spectra a, deg), which means all the three pillar[5]arenes
have similar binding modes with guest 9. There may exist multiple
CeH/
p interactions and CeH/O (N) hydrogen bonding in-
teractions between the host and guest. These interactions con-
tribute to the formation of the threaded structures.
2.3. Complexation stoichiometries and the comparison of
association constants between model compound 9 and pillar
[5]arenes
It is essential to know the binding stoichiometries of pillar[5]
arenes 1e3 with 9. From integrations of all peaks, the stoichiome-
tries of all three complexation systems were determined to be 1:1.
This was further confirmed by electrospray ionization mass spec-
trometry (ESI-MS). As shown in Fig. 3, all equimolar mixtures of 1
and 9, 2 and 9, and 3 and 9 have strong mass fragments of
[HIGþH]þ: m/z 1170.0 (100%) for [1I9þH]þ, m/z 1310.3 (100%) for
[2I9þH]þ, and m/z 1590.5 (100%) for [3I9þH]þ. No peaks with
other complexation stoichiometries were found. The association
constants Ka of 1I9, 2I9, and 3I9 calculated from integrations of
Fig. 3. Electrospray ionization mass spectra of equimolar CHCl3 solutions of 9 with (a)
1, (b) 2, and (c) 3.
complexed and uncomplexed species were (4.4ꢁ0.3)ꢂ102 Mꢀ1
,

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P. Wei et al. / Tetrahedron 68 (2012) 9179e9185
(5.5ꢁ0.2)ꢂ102 Mꢀ1, and (2.05ꢁ0.25)ꢂ102 Mꢀ1, respectively. The Ka
value of 2I9 is the largest among the three values, indicating that
host 2 is the most suitable wheel for the axle 9. A reasonable ex-
2.5. NOESY NMR experiments
The assignment and correlation of the protons of rotaxanes 10,11,
and 12 were validated by NOESY NMR spectra, which were all ob-
tained in chloroform-d. As shown in Fig. 5, the NOESY NMR
planation is that there may be more CeH/
p
interactions,10d,p
CeH/O (N)10g interactions between ethyl groups of DEP[5] with
the axle than methyl groups of DMP[5]. For DBP[5], the decreased
association constant compared with DEP[5] can be ascribed to the
steric hindrance of butyl groups. The order of association constants
between model compound 9 and pillar[5]arenes was consistent
with the sequence of the yields of the three corresponding rotax-
anes 10e12.
2.4. 1H NMR characterization of rotaxanes
Proton NMR spectra of the dumbbell-shaped component 7, [2]
rotaxane 10, and DMP[5] in chloroform-d are shown in Fig. 4
(spectra aec). Protons H7ceH7f of compound 7 shifted downfield
slightly due to the deshielding effect of the electron-rich cavity of
DMP[5]. The aromatic protons H1a, bridging methylene protons H1b
,
and methoxy protons H1c on 1 moved upfield after the formation of
rotaxane 10. Furthermore, protons H7heH7j of the alkyl chain of
compound 1 in particular show relatively bigger upfield shifts.
Protons H7h moved upfield from 4.35 ppm to 2.78 ppm, and protons
Hi and Hj shifted upfield from 1.96 ppm and 1.35 ppm to ꢀ0.92 ppm
and ꢀ2.18 ppm, respectively. Rotaxane 10 in polar solvent DMSO-d6
was also investigated for comparison and similar chemical shift
changes were observed (Fig. S31), confirming the formation of
a stable mechanically interlocked structure between DMP[5] and
the ‘axle’ 7. We also compared chemical shift changes between
‘axle’ 7, host 2 or 3 and rotaxane 11 or 12. Similar chemical shift
changes were also observed and the comparison of 1H NMR spectra
of 11 and 12 in chloroform-d or in DMSO-d6 also confirmed the
formation of rotaxanes.
Fig. 5. Partial NOESY NMR analysis of 11 in CDCl3 with a mixing time of 200 ms
(400 MHz, 20 ꢃC).
1
Fig. 4. H NMR spectra (400 MHz, CDCl3, 22 ꢃC) of (a) 10.0 mM 1, (b) 10.0 mM rotaxane 10, (c) 10.0 mM 7, (d) 10.0 mM rotaxane 11, (e) 10.0 mM 2, (f) 10.0 mM rotaxane 12, (g)
10.0 mM 3. The italic style in spectrum f denotes protons of rotaxane 12.

P. Wei et al. / Tetrahedron 68 (2012) 9179e9185
9183
examination of 11 exhibit unequivocal correlationpeaks between the
signals of triazole protons H7g, methylene protons H7f, aromatic
protons H7e of the guest component and those of the aromatic pro-
tons H2a andethylprotonsH2c andH2d ofthehostcomponent;seethe
NOE cross-peaks B, C, D, F, G and H, respectively. However, no cross-
peaks between protons H7aeH7d of the guest component and the
protons of the host component were observed, indicating that the
DEP[5] bead does not reach this part of the dumbbell-shaped com-
ponent. In the alkyl chain region of the guest, there are also corre-
lations between protons H7h and H7i of the guest and protons H2a of
the host, which are denoted as A and E. All these correlation signals
indicate that in chloroform-d the alkyl chain is incorporated into the
cavity of pillar[5]arene 2. NOESY NMR spectra of the other two
rotaxanes show similar correlation signals. However, rotaxane 10 has
the fewest correlations since its macrocycle DMP[5] has the shortest
methoxygroups (Fig. S32) and rotaxane 12 has the most signals since
its macrocycle DBP[5] has longest butoxy moieties (Fig. S33).
temperature for 2 h. Then the solution was treated with 3,5-
dinitrobenzoyl chloride (0.55 mmol) in the presence of Et3N
(100 mL) in an ice-water bath. After complete addition, the mixture
was stirred at room temperature for 48 h under nitrogen gas pro-
tection. Removal of chloroform followed by flash column chroma-
tography using petroleum ether/dichloromethane (10:1, v/v) as the
eluent gave the desired products as red solids.
4.2. [2]Rotaxane 10
Yield: 23%. Mp 74.9e76.1 ꢃC. 1H NMR (400 MHz, CDCl3, room
temperature) d (ppm): 9.08 (s, 6H), 7.54 (s, 2H), 7.52 (s, 4H), 7.16 (d,
4H, J¼8.0 Hz), 6.77 (s, 10H), 5.46 (s, 4H), 5.32 (s, 4H), 3.64 (s, 10H),
3.53 (s, 30H), 2.79 (s, 4H), ꢀ0.91 (s, 4H), ꢀ2.17 (s, 2H). 13C NMR
(100 MHz, CDCl3, 22 ꢃC)
d (ppm): 162.3, 158.7, 150.3, 148.3, 142.9,
131.0, 128.8, 127.4, 122.1, 114.9, 113.9, 68.2, 60.3, 56.0, 49.4, 29.2,
28.9, 26.8, 20.9, 14.1. Low-resolution ESI-MS: m/z 1618.7 (100%)
[Mþ2H]þ. HR ESI-MS: m/z calcd for [MþNa]þ C84H84N10O24Na
1639.5552, found 1639.5614, error 3.8 ppm.
Combining these NOESY results and 1H NMR spectra studies
mentioned above, we can definitely conclude pillar[5]arenes are lo-
cated at the central part of the guest. The longer the alkoxy groups of
the pillar[5]arene are, the more correlations between the host and
guest are, and thus we can reasonably speculate that the bigger steric
hindrancethereshouldbe. Moreover, thesequenceoftheyieldsofthe
rotaxanes is consistent with the order of the association constants
between model compound 9 and the corresponding pillar[5]arenes,
suggesting that the association strength between the ‘wheel’ and the
‘axle’playsanimportantroleinthepreparationofrotaxanes(Table 1).
4.3. [2]Rotaxane 11
Yield: 27%. Mp 77.6e78.4 ꢃC. 1H NMR (400 MHz, CDCl3, room
temperature) d (ppm): 9.17 (s, 2H), 9.12 (s, 4H), 7.72 (s, 2H), 7.49 (d,
4H, J¼8.0 Hz), 7.13 (d, 4H, J¼8.0 Hz), 6.88 (s, 10H), 5.41e5.49 (m,
4H), 5.30 (s, 4H), 3.73e3.80 (m, 20H), 3.71 (s, 10H), 2.92e3.00 (m,
2H), 2.81e2.88 (m, 2H), 1.32 (t, 30H, J¼16.0 Hz), (ꢀ0.80) to (ꢀ0.70)
(m, 4H), ꢀ2.17 (t, 2H, J¼16.0 Hz). 13C NMR (100 MHz, CDCl3, 22 ꢃC)
Table 1
d
(ppm): 162.3, 158.9, 149.6, 148.4, 142.6, 129.3, 129.0, 127.1, 122.2,
Ka (Mꢀ1) of complexes 1I9, 2I9 and 3I9 in CHCl3 at 22 ꢃC and the yields of the
114.8, 68.3, 64.2, 61.8, 49.5, 29.6, 29.1, 26.7, 20.8, 15.2. Low-
resolution ESI-MS: m/z 1780.9 (100%) [MþHþNa]þ. HR ESI-MS
m/z calcd for [MþþNa]þ C94H104N10O24Na 1779.7117, found
1779.7046, error ꢀ4.0 ppm.
corresponding pillar[5]arene-based [2]rotaxanes
1I9
2I9
3I9
Association constants (Mꢀ1
Yields of the corresponding 23%
[2]rotaxanes
)
(4.4ꢁ0.3)ꢂ102 (5.5ꢁ0.2)ꢂ102 (2.05ꢁ0.25)ꢂ102
27%
16%
4.4. [2]Rotaxane 12
Yield: 16%. Mp 134.2e135.8 ꢃC. 1H NMR (400 MHz, CDCl3, room
temperature) d (ppm): 9.22 (s, 2H), 9.15 (s, 4H), 7.74 (s, 2H), 7.48 (d,
3. Conclusions
4H, J¼8.0 Hz), 7.12 (d, 4H, J¼8.0 Hz), 6.90 (s, 10H), 5.41e5.46 (m,
4H), 5.20e5.27 (m, 4H), 3.70e3.77 (m, 20H), 3.65e3.70 (m, 10H),
2.97e3.03 (m, 2H), 2.82e2.88 (m, 2H), 1.61e1.73 (m, 20H),
1.39e1.48 (m, 20H), 0.90 (t, 30H, J¼16.0 Hz), ꢀ0.68 (s, 2H), ꢀ0.81 (s,
2H), ꢀ2.23 (d, 2H, J¼8.0 Hz). 13C NMR (100 MHz, CDCl3, 22 ꢃC)
In summary, we have synthesized an alkane functionalized with
triazole moieties and studied its binding tothree pillar[5]arenes. The
results obtained from 1H NMR and ESI mass spectrometry indicated
the formation of [2]pseudorotaxanes, where the alkane chain and
triazoles play crucial roles in the hosteguest complexation. CeH/O
d
(ppm): 162.3, 159.1, 149.7, 148.5, 142.5, 129.4, 129.0, 127.0, 122.0,
(N) hydrogen bonds and CeH/p interactions are the possible
115.3, 114.8, 114.7, 68.3, 61.9, 49.5, 31.9, 29.1, 26.6, 22.6, 20.6, 19.3,
13.9. Low-resolution ESI-MS: m/z 2039.9 (100%) [Mþ2H]þ. HR ESI-
MS m/z calcd for [MþH]þ C114H145N10O242039.0459, found
2039.0403, error ꢀ2.7 ppm.
driving forces. These multiple noncovalent interactions may jointly
contribute to the complex formation and considerably reinforce the
complex stability. Then three pillar[5]arene-based [2]rotaxanes
were constructed based on this new recognition motif. From 1H
NMR, electrospray ionization mass spectrometry, and NOESY char-
acterizations, we confirmed the formation of [2]rotaxanes and we
can reasonably speculate that pillar[5]arenes are located at the
central part of the ‘axle’. The sequence of the yields of these rotax-
anes was consistent with the order of the association constants
between model compound 9 and the corresponding pillar[5]arene
macrocycles, which further illustrated the importance of this rec-
ognition motif to the preparation of rotaxanes. Our current efforts
are focused on extending this new recognition motif to fabricate
functional molecular machines and larger supramolecular systems.
4.5. 1,5-Bis(4-(phenoxymethyl)-1H-1,2,3-triazol-1-yl)pentane
(9)
A mixture of 8 (1.32 g, 10 mmol), 1,5-diazidopentane (0.77 g,
5 mmol), CuSO4$5H2O (0.25 g, 1 mmol), sodium ascorbate (0.6 g,
3 mmol) in DMF/H2O (5:1) (100 mL) was refluxed under N2 at-
mosphere for 24 h. The solvent was removed by a rotary evaporator
and the residue was purified by chromatography on silica gel (pe-
troleum ether/ethyl acetate, v/v 1:1) to yield a white solid (1.0 g,
48%). Mp 104e105 ꢃC. 1H NMR (400 MHz, CDCl3, room tempera-
ture)
J¼16.0 Hz), 5.20 (s, 4H), 4.33 (t, 4H, J¼12.0 Hz), 1.90e1.97 (m, 4H),
1.28e1.36 (m, 2H). 13C NMR (100 MHz, CDCl3, 22 ꢃC)
(ppm): 157.6,
d
(ppm): 7.57 (s, 2H), 7.29 (t, 4H, J¼16.0 Hz), 6.97 (t, 6H,
4. Experimental section
d
4.1. General method for the syntheses of [2]rotaxanes 10e12
143.7, 129.0, 120.7, 114.1, 61.3, 49.3, 28.9, 22.7. Low-resolution ESI-
MS: m/z 441.2 (17%) [MþNa]þ and 419.3 (100%) [MþH]þ. HR ESI-MS
m/z calcd for [M]þ C23H26N6O2 418.2117, found 418.2122, error
1.2 ppm.
A mixture of 6 (0.250 mmol) and the corresponding pillar[5]
arene (1e3, 0.625 mmol) in CHCl3 (15.0 mL) was stirred at room

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2011, 40, 3656e3676; (e) Yan, X.; Zhang, M.; Wei, P.; Zheng, B.; Chi, X.; Ji, X.;
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A mixture of 5 (1.62 g, 10 mmol), 1,5-diazidopentane (0.62 g,
4.0 mmol), CuSO4$5H2O (0.25 g, 1.0 mmol) and sodium ascorbate
(0.60 g, 3.0 mmol) in DMF/H2O (5:1) (100 mL) was refluxed under
N2 atmosphere for 24 h. The solvent was removed and the residue
was purified by chromatography on silica gel (petroleum ether/
ethyl acetate, v/v 1:2) to yield a white solid (1.2 g, 60%). Mp
107.6e109.1 ꢃC. 1H NMR (400 MHz, CDCl3, room temperature)
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d
(ppm): 7.55 (s, 2H), 7.26 (s, 4H), 6.96 (d, 4H, J¼8.0 Hz), 4.62 (s,
4H), 4.33 (t, 4H, J¼12.0 Hz), 1.91e1.95 (m, 4H), 1.74 (s, 4H),
1.30e1.32 (m, 2H). 13C NMR (100 MHz, CDCl3, 22 ꢃC)
(ppm):
d
157.6, 144.2, 133.7, 128.6, 122.5, 114.8, 64.8, 62.0, 49.8, 29.3, 23.2.
Low-resolution ESI-MS: m/z 501.4 (100%) [MþNa]þ. HR ESI-MS m/z
calcd for [MþNa]þ C25H30N6O4Na 501.2221, found 501.2208,
error ꢀ2.6 ppm.
4.7. Compound 7
3,5-Dinitrobenzoyl chloride (143 mg, 0.62 mmol) was added to
a solution of 6 (136 mg, 0.28 mmol) in CHCl3 (25 mL) at 0 ꢃC. Then
Et3N (120 mL) was added dropwise and the mixture was stirred at
room temperature for 24 h. The solvent was removed and the
residue was purified by column chromatography on silica gel
(dichloromethane) to yield a white solid (80 mg, 33%). Mp
67.6e68.5 ꢃC. 1H NMR (400 MHz, CDCl3, room temperature)
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d
(ppm): 9.16 (s, 2H), 9.11 (s, 4H), 7.60 (s, 2H), 7.39 (d, 4H, J¼8.0 Hz),
6.99 (d, 4H, J¼8.0 Hz), 5.38 (s, 4H), 5.17 (s, 4H), 4.34 (t, 4H,
J¼12.0 Hz), 1.91e1.98 (m, 4H), 1.30e1.35 (m, 2H). 13C NMR
(100 MHz, CDCl3, 22 ꢃC)
d (ppm): 162.4, 158.6, 148.5, 143.7, 130.7,
129.4, 127.2, 122.3, 114.9, 68.2, 61.9, 49.9, 29.4, 23.2. Low-resolution
ESI-MS: m/z 905.4 (10%) [MþK]þ, 889.6 (100%) [MþNa]þ, and 867.4
(7%) [MþH]þ. HR ESI-MS m/z calcd for [MþNa]þ C39H34N10O14Na
889.2148, found 889.2139, error ꢀ1.0 ppm.
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Acknowledgements
This work was supported by the National Natural Science
Foundation of China (20834004, 91027006, and 21125417), the
Fundamental Research Funds for the Central Universities
(2012QNA3013), Program for New Century Excellent Talents in
University, and Zhejiang Provincial Natural Science Foundation of
China (R4100009).
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Supplementary data
Determination of association constants, 1H and 13C NMR spectra,
electrospray ionization mass spectra, and other materials. Supple-
mentary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2012.09.018.
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