Preparation of pillar[n]arenes by cyclooligomerization of 2,5-dialkoxybenzyl alcohols or 2,5-dialkoxybenzyl bromides

Article abstract of DOI:10.1002/ejoc.201100698

The facile and efficient preparation of pillar[n]arenes (n = 5 or 6) was achieved by cyclooligomerization of 2,5-dialkoxybenzyl alcohols or 2,5-dialkoxybenzyl bromides with an appropriate Lewis acid catalyst at room temperature. The mechanism for this cyclooligomerization is presumed to be a Friedel-Crafts alkylation.

Full text of DOI:10.1002/ejoc.201100698

FULL PAPER
DOI: 10.1002/ejoc.201100698
Preparation of Pillar[n]arenes by Cyclooligomerization of 2,5-Dialkoxybenzyl
Alcohols or 2,5-Dialkoxybenzyl Bromides
Yingjie Ma,[a] Zibin Zhang,[a] Xiaofan Ji,[a] Chengyou Han,[a] Jiuming He,[b] Zeper Abliz,[b]
Weixiang Chen,[a] and Feihe Huang*[a]
Keywords: Supramolecular chemistry / Host–guest systems / Cyclooligomerization / Calixarenes / Macrocycles / Arenes /
Pillar[n]arenes
The facile and efficient preparation of pillar[n]arenes (n = 5
or 6) was achieved by cyclooligomerization of 2,5-dialk-
oxybenzyl alcohols or 2,5-dialkoxybenzyl bromides with an
appropriate Lewis acid catalyst at room temperature. The
mechanism for this cyclooligomerization is presumed to be a
Friedel–Crafts alkylation.
acid as the catalyst at room temperature.[5a] With this
method, both 1,4-dialkoxypillar[5]arenes and 1,4-dialk-
oxypillar[6]arenes can be synthesized. Nevertheless, the
preparation of the starting reactants, 1,4-dialkoxy-2,5-bis-
(alkoxymethyl)benzenes, is not easy. For the further investi-
gation of pillararenes in supramolecular chemistry, the
search for facile and efficient preparation methods is a nec-
essary and urgent mission.
Introduction
The preparation of new macrocyclic hosts plays an im-
portant role in supramolecular chemistry, as every genera-
tion makes their supramolecular chemistry more versatile.[1]
A new kind of macrocyclic host, called pillar[n]arenes,[2] has
attracted increasing attention over the past few years. Their
structures are similar to those of calixarenes,[3,4] but they
are more symmetrical and rigid, which provides them with
some interesting physical, chemical, and host–guest proper-
ties. Until now, two kinds of pillararenes, pillar[5]arenes and
pillar[6]arenes, containing five and six units, respectively,
have been reported. Their syntheses,[2a,2c,2f,5a,5b,6a,6c] confor-
Results and Discussion
Herein, we report a new method to synthesize DMpil-
mational mobility,[2e,2g,6] derivatization,[2b,11a] host–guest lar[5]arene by condensation of 2,5-dimethoxybenzyl alcohol
complexation with organic salts,[6a,6c,7,8,12] and self-assem- (2) with an appropriate Lewis acid catalyst in CH2Cl2 at
bly[2d,6b,11b] have been explored. However, methods to make room temperature (Scheme 1). In this reaction, various
pillararenes are still limited. To date, only three methods Lewis acids, such as FeCl3, AlCl3, SnCl4, and BF3·
have been reported. In 2006, Kanai et al. reported the first O(C2H5)2, can be used as a catalyst.
method, by which a five-membered ring was synthesized
successfully from 1,4-dimethoxy-2,5-xylylenedibromide in
low yield using a Friedel–Crafts reaction.[13,14] In 2008,
Ogoshi et al. reported the second method, by which 1,4-
dimethoxypillar[5]arene (DMpillar[5]arene) was prepared
rapidly and easily by condensation of 1,4-dimethoxybenz-
ene and paraformaldehyde with BF3·O(C2H5)2 as the cata-
lyst.[2a] However, this method is limited to the preparation
of pillar[5]arenes. More recently, Cao and Meier et al. re-
ported the third method by the condensation of 1,4-dialk- 2.
oxy-2,5-bis(alkoxymethyl)benzenes using p-toluenesulfonic
Scheme 1. Synthesis of DMpillar[5]arene from the condensation of
First, we investigated the effect of different Lewis acids
on the cyclization reaction using CH2Cl2 as the solvent. The
results showed that a solution of 2 in CH2Cl2 turned green
immediately when SnCl4 or BF3·O(C2H5)2 was added. The
reactant 2 was consumed in about one minute. This showed
that both SnCl4 and BF3·O(C2H5)2 can promote the cycli-
zation reaction efficiently. In addition, FeCl3 and AlCl3 can
also promote the reaction. With either FeCl3 and AlCl3 as
[a] Department of Chemistry, Zhejiang University,
Hangzhou 310027, P. R. China
Fax: +86-571-8795-3189
E-mail: fhuang@zju.edu.cn
[b] Institute of Materia Medica, Chinese Academy of Medical
Sciences and Peking Union Medical College,
Beijing 100050, P. R. China
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201100698.
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F. Huang et al.
FULL PAPER
the catalyst, the reaction was finished in about three min-
utes, a little longer than when SnCl4 or BF3·O(C2H5)2 was
used. When ZnCl2 was used as the catalyst, the cyclization
occurred very slowly, and a reaction time of 10 h was re-
quired. Furthermore, the color of the reaction mixture after
completion of the reaction was white, whereas the color was
deep green when the other Lewis acids were used. Using
different Lewis acids as the catalyst gave different yields
(Table 1). Similar yields of DMpillar[5]arene were achieved
with FeCl3, AlCl3, and BF3·O(C2H5)2 and a lower yield was
obtained with SnCl4. However, when ZnCl2 was used as the
catalyst, the amount of the product obtained was so little
that it could be detected only by MS. Therefore, FeCl3,
AlCl3, or BF3·O(C2H5)2 are the best choice of catalyst in
the preparation of DMpillar[5]arene from the condensation
of 2 in CH2Cl2.
Scheme 2. Possible mechanism of the cyclization reaction of 2 to
form DMpillar[n]arene.
Table 1. Cyclization reactions using different Lewis acids as the cat-
alyst for the room temperature condensation of 2 in CH2Cl2.
Catalyst (1 equiv.)
Reaction time (min)
Yield (%)
FeCl3
BF3·O(C2H5)2
AlCl3
SnCl4
ZnCl2
3
3
3
3
3
39
38
35
25
trace
Scheme 3. Synthesis of DMpillar[5]arene from the condensation of
3.
The mechanism of this cyclization reaction is presumably
based on a Friedel–Crafts alkylation (Scheme 2).[9,10] With
the catalyst, 2 is converted to its carbocation, which un-
dergoes reaction with the benzene ring of another molecule
of 2. Because of the orientation effect of the benzyl alcohol
group, the benzyl carbocation group is attached at the 4-
position of 2 to give a dimer. In the same way, other oligo-
mers can form. At last, these oligomers form rings through
cyclocondensation to give the corresponding macrocyclic
compounds. We wondered why the five-membered ring,
Table 2. Cyclization reactions using different Lewis acids as the cat-
alyst for the room temperature condensation of 3 in CH2Cl2.
Catalyst (1 equiv.)
Reaction time [min]
Yield [%]
ZnCl2
AlCl3
SnCl4
FeCl3
3
3
3
3
3
40
37
35
34
trace
BF3·O(C2H5)2
DMpillar[5]arene, was the main product. Its crystal struc- was required for the condensation to finish when BF3·
ture shows that it is a regular pentagon,[2a] so the angle O(C2H5)2 was used as the catalyst. The yields of the reac-
between the two bridging carbon–carbon bonds is 108°, tions using different catalysts in CH2Cl2 for three minutes
which is very close to the normal bond angle of the sp3 are shown in Table 2, and ZnCl2 produced the highest yield.
carbon atom, 109°28Ј. Therefore, the DMpillar[5]arene With BF3·O(C2H5)2 as the catalyst, trace product was ob-
structure should have a lowest energy and be the most tained. When FeCl3, AlCl3 or SnCl4 was used, the yields
stable macrocycle compared to other cyclic compounds were about the same. These results are different to those
containing different numbers of repeat units.
using 2 as the reactant. However, the highest yield of
If the mechanism is correct, 2,5-dimethoxybenzyl bro- DMpillar[5]arene using 3 is very close to that obtained with
mide (3) could also be used to synthesize DMpillar[5]arene, 2.
similar to a reported method for calixarenes,[4] as it could
A detailed study of the reactions of starting compounds
also be converted to the carbocation under the influence 5a–c [R = pentyl (5a), hexyl (5b), and octyl (5c)] revealed
of a Lewis acid and undergo Friedel–Crafts alkylation.[10] that the corresponding pillararenes were obtained (Table 3).
Therefore, we replaced 2 with 3 and repeated the cyclization Using 5a or 5b as the starting compound, the cyclic penta-
reaction (Scheme 3 and Table 2). DMpillar[5]arene was ob- mers were obtained with similar yields, which were higher
tained as expected, consistent with the proposed mecha- than those reported (Table 3).[2c] However, 5c yielded not
nism.
only the cyclic pentamer 1,4-dioctyloxypillar[5]arene (65c),
The Lewis acids, FeCl3, AlCl3, BF3·O(C2H5)2, ZnCl2, but also the higher cyclooligomer 1,4-dioctyloxypillar[6]ar-
and SnCl4 were also investigated for this reaction and all ene (66c) in yields of 14 and 13%, respectively. Further-
were found to promote the cyclization reaction. When more, the yield of 66c was higher than those (8,[5a] 11,[5a]
FeCl3, AlCl3, ZnCl2, or SnCl4 was added, the solution of 3 and 4.6%[8]) of all the other pillar[6]arenes reported to date.
in CH2Cl2 turned green immediately. However, 24 h Both 65c and 66c are white solids and their melting points
5332
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Eur. J. Org. Chem. 2011, 5331–5335

Preparation of Pillar[n]arenes by Cyclooligomerization
are 97.9–99.4 and 76.0–78.9 °C, respectively. These values
are lower than that of DMpillar[5]arene (248.8 °C),[2a]
probably due to the incorporation of longer, flexible alkyl
chains.
Conclusions
We have demonstrated that pillararenes can be obtained
by the condensation of 2,5-dialkoxybenzyl alcohol (2) and
2,5-dialkoxybenzyl bromide (3) with an appropriate Lewis
acid catalyst at room temperature in a short time. The
mechanism of this cyclization reaction is presumed to be a
Friedel–Crafts alkylation. The effect of different Lewis ac-
ids on the cyclization reaction was investigated. The results
showed that the effects of different Lewis acids on the cycli-
zation reactions of 2 and 3 were different. When 2 was used
as the reactant, the appropriate catalyst was FeCl3, AlCl3,
SnCl4, or BF3·O(C2H5)2, whereas when 3 was used, the ap-
propriate catalyst was FeCl3, AlCl3, ZnCl2 or SnCl4. Using
this method, pillar[n]arenes (n = 5, 6) with different alkoxy
substituents were prepared successfully. Our method makes
it possible to prepare pillar[5]arenes and pillar[6]arenes eas-
ily and efficiently from the cyclization of relatively available
2,5-dialkoxybenzyl alcohols and 2,5-dialkoxybenzyl bro-
mides. This should be helpful for investigations on the ap-
plications of pillararenes, especially pillar[6]arenes, in host–
guest chemistry.
Table 3. Preparation of 65a–c and 66c with different alkoxy substit-
uents R.
Starting
compound
R
Product
Yield
[%]
Product Yield [%]
Experimental Section
5a
5b
5c
pentyl
hexyl
octyl
65a
65b
65c
41[a]
43[b]
14
–
–
–
–
13
General: 2,5-Dimethoxybenzaldehyde, 2,5-dihydroxybenzaldehyde,
bromooctane, bromopentane, bromohexane, boron trifluoride ethyl
ether complex, FeCl3, ZnCl2, SnCl4, AlCl3, and CH2Cl2 were rea-
gent grade and used as received. Solvents were either employed as
purchased or dried according to procedures described in the litera-
ture. 1H NMR spectra were collected with a Varian Unity INOVA-
400 spectrometer with TMS. 13C NMR spectra were recorded with
a Varian Unity INOVA-400 spectrometry at 100 MHz. Mass spec-
tra were performed with a Bruker Esquire 3000 plus mass spec-
trometer (Bruker–Franzen Analytik GmbH Bremen, Germany)
equipped with ESI interface and ion trap analyzer. High resolution
mass spectra were obtained with a Bruker 7-Tesla FT-ICRMS
equipped with an electrospray source (Billerica, MA, USA). The
melting points were measured with an automatic melting point ap-
paratus (SHPSIC WRS-2).
66c
[a] The reported yield was 13.7%.[2c] [b] The reported yield was
18.2%.[2c]
1H NMR spectra of 65c and 66c show that the signal
arising from the phenylene protons H1 shifted upfield from
6.85 for 65c to 6.70 ppm for 66c, and the methylene protons
H3 shifted from 3.84 for 65c to 3.70 ppm for 66c (Figure 1).
A possible reason is that 66c contains more benzene rings
than 65c so the shielding is stronger. Furthermore, it was
found that the signals of methylene protons H2 and H3 of
66c overlap, and those of 65c do not.
Synthesis of 2: To a solution of 2,5-dimethoxybenzaldehyde (3.32 g,
20.0 mmol) in MeOH, NaBH4 (1.13 g, 30.0 mmol) was added at
0 °C. The mixture was stirred overnight at room temperature. The
solvent was removed by evaporation. To the residue, H2O/CH2Cl2
(v/v = 1:1, 100 mL) was added. The organic layer was dried with
anhydrous Na2SO4. After filtration, solvents were evaporated to
give a colorless oil (3.32 g, 99%). 1H NMR (400 MHz, CDCl3,
room temperature): δ = 6.90 (s, 1 H), 6.78 (s, 2 H), 4.64 (s, 2 H),
3.79 (s, 3 H), 3.75 (s, 3 H) ppm. 13C NMR (100 MHz, CDCl3,
room temperature): δ = 153.7, 151.4, 130.3, 114.6, 112.9, 111.2,
61.60, 51.80 ppm. ESI-MS: m/z = 191.1 [M + Na]+ (100). HRMS:
m/z calcd. for [M]+ C9H12O3, 168.0786; found 168.0788, error
0.2 ppm.
Synthesis of DMpillar[5]arene from 2: To a solution of 2 (0.673 g,
4.00 mmol) in CH2Cl2, catalyst [4.00 mmol: BF3·O(C2H5)2, FeCl3,
ZnCl2, SnCl4 or AlCl3] was added. After the mixture was stirred at
room temperature for 3 min, the mixture was washed twice with
deionized water (30 mL). The organic layer was dried with anhy-
drous Na2SO4 and evaporated to afford the crude product, which
was isolated by flash column chromatography using petroleum
Figure 1. 1H NMR spectra (400 MHz, CDCl3, 20 °C) of (a) 65c
and (b) 66c.
Eur. J. Org. Chem. 2011, 5331–5335
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F. Huang et al.
FULL PAPER
ether/ethyl acetate (v/v = 6:1) as the eluent to give the product as a
and NaBH4 (2.55 g, 67.4 mmol) was added at 0 °C. Then the mix-
white solid [BF3·O(C2H5)2: 0.225 g, 38%; FeCl3: 0.235 g, 39%; ture was stirred overnight at room temperature and the solvent was
ZnCl2: trace; SnCl4: 0.15 g, 25%; AlCl3: 0.210 g, 35%]; m.p. 248.1– removed by evaporation. To the residue, H2O/CH2Cl2 (v/v = 1:1,
249.0 °C. 1H NMR (400 MHz, CDCl3, room temperature): δ = 6.88 200 mL) was added. The organic layer was dried with anhydrous
(s, 10 H), 3.78 (s, 10 H), 3.74 (s, 30 H) ppm. 13C NMR (100 MHz,
CDCl3, room temperature): δ = 151.02, 128.43, 114.29, 55.99, 29.88
ppm. ESI-MS: m/z = 773.4 [M + Na]+ (100%), 751.4 [M + H]+,
768.5 [M + NH4]+. HRMS: m/z calcd. for [M]+ C52H46O5,
750.3345; found 750.3352, error 0.2 ppm.
Na2SO4. After filtration, solvents were evaporated to give the prod-
uct as a brown liquid (9.4 g, 91%). 1H NMR (400 MHz, CDCl3,
room temperature): δ = 6.87 (d, J = 1.9 Hz, 1 H), 6.75 (d, J =
2.6 Hz, 2 H), 4.64 (s, 2 H), 3.91 (m, 4 H), 2.49 (s, 1 H), 1.44 (m, 4
H), 1.38–1.28 (m, 8 H), 0.92–0.89 (m, 6 H) ppm. 13C NMR
(100 MHz, CDCl3, room temperature): δ = 153.27, 150.96, 130.55,
115.44, 113.87, 112.31, 68.77, 62.10, 31.37, 29.51, 25.92, 22.74,
14.14 ppm. HRMS: m/z calcd. for [M]+ C19H32O3, 308.2356; found
308.2351, error 1.6 ppm.
Synthesis of 3: To a solution of 2 (7.52 g, 44.7 mmol) in CH2Cl2,
PBr3 (7.97 mL, 83.9 mmol) was added. After the mixture was
stirred at room temperature overnight, deionized water (30 mL)
was added. The organic layer was washed twice with deionized
water (100 mL). The organic layer was dried with anhydrous
Na2SO4 and evaporated to afford the product as a white solid
(9.58 g, 93%); m.p. 67.0–68.5 °C. 1H NMR (400 MHz, CDCl3,
room temperature): δ = 6.91 (d, J = 2.2 Hz, 1 H), 6.82 (m, 2 H),
4.54 (s, 2 H), 3.85 (s, 3 H), 3.77 (s, 3 H) ppm. 13C NMR (100 MHz,
CDCl3, room temperature): δ = 153.54, 151.79, 127.04, 116.52,
115.16, 112.31, 55.32, 55.89, 29.11 ppm. HRMS: m/z calcd. for
[M]+ C9H11O2Br, 229.9942; found 229.9947, error 0.2 ppm.
Synthesis of 5c: A mixture of 2,5-dihydroxybenzaldehyde (5.52 g,
40 mmol), K2CO3 (16.56 g, 120 mmol) and bromooctane (27.9 mL,
160 mmol) in CH3CN (250 mL) was heated to reflux overnight.
After cooling, the mixture was filtered to obtain a black solution.
The solution was concentrated and purified by silica gel flash col-
umn chromatography (petroleum ether/ethyl acetate, v/v = 200:1)
to obtain the product as a brown oil (13.9 g). The brown oil (13.9 g,
38.3 mmol) was dissolved in CH2Cl2/MeOH (v/v = 1:1) and NaBH4
(2.90 g, 76.7 mmol) was added at 0 °C. The mixture was stirred
overnight at room temperature and the solvent was removed by
evaporation. To the residue, H2O/CH2Cl2 (v/v = 1:1, 100 mL) was
added. The organic layer was dried with anhydrous Na2SO4. After
filtration, solvents were evaporated to give the product as a white
solid (13.7 g, 98%); m.p. 38.4–39.8 °C. 1H NMR (400 MHz,
CDCl3, room temperature): δ = 6.88 (d, J = 2.2 Hz, 1 H), 6.78 (m,
2 H), 4.67 (d, J = 5.3 Hz, 2 H), 3.97 (t, J = 6.5 Hz, 2 H), 3.92 (t,
J = 6.6 Hz, 2 H), 2.45 (s, 1 H), 1.83–1.72 (m, 4 H), 1.56–1.41 (m,
4 H), 1.38–1.28 (m, 16 H), 0.90 (t, J = 6.6 Hz, 6 H) ppm. 13C NMR
(100 MHz, CDCl3, room temperature): δ = 153.25, 151.07, 130.45,
115.49, 113.93, 112.29, 68.81, 62.44, 32.02, 29.46, 26.26, 22.66,
14.29 ppm. HRMS: m/z calcd. for [M]+ C23H40O3, 364.2977; found
364.2973, error 0.2 ppm.
Synthesis of DMpillar[5]arene from 3: To a solution of 3 (0.924 g,
4.00 mmol) in CH2Cl2, catalyst [4 mmol: BF3·O(C2H5)2, FeCl3,
ZnCl2, SnCl4 or AlCl3] was added. After the mixture was stirred
at room temperature for 3 min, the mixture was washed twice with
deionized water (30 mL). The organic layer was dried with anhy-
drous Na2SO4 and evaporated to afford the crude product, which
was isolated by flash column chromatography using petroleum
ether/ethyl acetate (v/v = 6:1) as the eluent to give the product as a
white solid [BF3·O(C2H5)2: trace; FeCl3: 0.205 g, 34%; ZnCl2:
0.241 g, 40%; SnCl4: 0.214 g, 35%; AlCl3: 0.220 g, 37%]; m.p.
1
248.1–249.0 °C. H NMR (400 MHz, CDCl3, room temperature):
δ = 6.88 (s, 10 H), 3.78 (s, 10 H), 3.74 (s, 30 H) ppm.
Synthesis of 5a: A mixture of 2,5-dihydroxybenzaldehyde (5.52 g,
40 mmol), K2CO3 (16.56 g, 120 mmol), and 1-bromopentane
(19.7 mL, 160 mmol) in CH3CN (250 mL) was heated to reflux
overnight. After cooling, the mixture was filtered to obtain a black
solution. The solution was concentrated and purified by silica gel
flash column chromatography (petroleum ether/ethyl acetate, v/v =
10:1) to obtain the product as a brown oil (9.2 g). The brown oil
(2.92 g, 10 mmol) was dissolved in CH2Cl2/MeOH (v/v = 1:1) and
NaBH4 (0.760 g, 20 mmol) was added at 0 °C. The resulting mix-
ture was stirred overnight at room temperature and the solvent was
removed by evaporation. To the residue, H2O/CH2Cl2 (v/v = 1:1,
100 mL) was added. The organic layer was dried with anhydrous
Synthesis of 65a: To a solution of 5a (1.16 g, 4.14 mmol) in CH2Cl2,
BF3·O(C2H5)2 (1.04 mL, 4.14 mmol) was added. After the mixture
was stirred at room temperature for 3 min, the mixture was washed
twice with deionized water (100 mL). The organic layer was dried
with anhydrous Na2SO4 and evaporated to afford the crude prod-
uct, which was isolated by flash column chromatography using pe-
troleum ether/ethyl acetate (v/v = 40:1) as the eluent to give the
product as a white solid (0.44 g, 41%). 1H NMR (400 MHz,
CDCl3, room temperature): δ = 6.70 (s, 10 H), 3.90 (s, 10 H), 3.83
(t, J = 6.1 Hz, 20 H), 1.73 (m, 20 H), 1.42–1.29 (m, 40 H), 0.91 (t,
J = 6.9 Hz, 30 H) ppm.
Na2SO4. After filtration, solvents were evaporated to give the prod-
1
uct as a brown liquid (2.80 g, 99%). H NMR (400 MHz, CDCl3, Synthesis of 65b: To a solution of 5b (0.617 g, 2.00 mmol) in
room temperature): δ = 6.86 (d, J = 1.9 Hz, 1 H), 6.74 (d, J =
3.4 Hz, 2 H), 4.63 (s, 2 H), 3.92 (t, J = 6.5 Hz, 2 H), 3.88 (t, J =
CH2Cl2, BF3·O(C2H5)2 (0.501 mL, 2.00 mmol) was added. After
the mixture was stirred at room temperature for 3 min, the mixture
6.6 Hz, 2 H), 1.78–1.73 (m, 4 H), 1.43–1.35 (m, 8 H), 0.94–0.91 (m, was washed twice with deionized water (100 mL). The organic layer
6 H) ppm. 13C NMR (100 MHz, CDCl3, room temperature): δ =
was dried with anhydrous Na2SO4 and evaporated to afford the
153.21, 150.97, 130.44, 115.49, 113.83, 112.23, 68.72, 62.10, 29.24, crude product, which was isolated by flash column chromatography
28.42, 22.62, 14.17 ppm. HRMS: m/z calcd. for [M]+ C17H28O3,
280.2039; found 280.2038, error 0.4 ppm.
using petroleum ether/ethyl acetate (v/v = 80:1) as the eluent to give
the product as a white solid (0.25 g, 43%). 1H NMR (400 MHz,
CDCl3, room temperature): δ = 6.66 (s, 10 H), 3.86 (s, 10 H), 3.79
(t, J = 6.2 Hz, 20 H), 1.71–1.58 (m, 20 H), 1.39 (m, 20 H), 1.29–
1.27 (m, 40 H), 0.87 (t, J = 6.9 Hz, 30 H) ppm.
Synthesis of 5b: A mixture of 2,5-dihydroxybenzaldehyde (5.52 g,
40 mmol), K2CO3 (16.56 g, 120 mmol) and bromohexane (22.5 mL,
160 mmol) in CH3CN (250 mL) was heated to reflux overnight.
After cooling, the mixture was filtered to obtain a black solution.
The solution was concentrated and purified by silica gel flash col-
umn chromatography (petroleum ether/ethyl acetate, v/v = 10:1) to
obtain the product as a brown oil (15 g). The brown oil (10.33 g,
33.7 mmol) was dissolved in CH2Cl2/MeOH (v/v = 1:1, 200 mL)
Synthesis of 65c and 66c: To a solution of 5c (7.29 g, 20 mmol) in
CH2Cl2, BF3·O(C2H5)2 (5.04 mL, 20.0 mmol) was added. After the
mixture was stirred at room temperature for 3 min, the mixture was
washed twice with deionized water (100 mL). The organic layer was
dried with anhydrous Na2SO4 and evaporated to afford the crude
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Preparation of Pillar[n]arenes by Cyclooligomerization
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product, which was isolated by flash column chromatography using
petroleum ether/ethyl acetate (v/v = 200:1) as the eluent to give the
products, 65c and 66c, both of which were white solids (65c: 1.00 g,
14%; m.p. 97.9–99.5 °C. 66c: 0.92 g, 13%; m.p. 76.0–79.1 °C).
Compound 65c was separated first and then 66c was eluted. 65c: 1H
NMR (400 MHz, CDCl3, room temperature): δ = 6.85 (s, 10 H),
3.84 (s, 20 H), 3.73 (s, 10 H), 1.81 (s, 20 H), 1.53–1.47 (m, 20 H),
1.35–1.23 (m, 80 H), 0.85 (t, J = 6.8 Hz, 30 H) ppm. 13C NMR
(100 MHz, CDCl3, room temperature): δ = 149.86, 128.30, 114.23,
68.28, 32.18, 30.38, 30.01, 29.63, 29.42, 26.67, 22.95, 14.34 ppm.
ESI-MS: m/z 1749.9 [M + NH4]+ (100%). HRMS: m/z calcd. for
[M + NH4]+ C115H194N1O10, 1749.47027; found 1749.47080, error
0.3 ppm. 66c: 1H NMR (400 MHz, CDCl3, room temperature): δ =
6.70 (s, 12 H), 3.76–3.72 (m, 36 H), 1.72–1.68 (m, 24 H), 1.42 (s,
24 H), 1.32–1.23 (m, 96 H), 0.87 (t, J = 6.7 Hz, 36 H) ppm. 13C
NMR (100 MHz, CDCl3, room temperature): δ = 150.70, 127.94,
115.20, 68.75, 32.22, 31.18, 30.18, 29.91, 29.66, 26.64, 22.97, 14.35
ppm. ESI-MS: m/z 1749.9 [M + NH4]+(100%). LRESIMS: m/z
2078.3 [M + H]+ (100%). HRMS: m/z calcd. for [M + NH4]+
C138H232N1O12, 2095.75745; found 2095.75517, error –1.09 ppm.
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Acknowledgments
This work was supported by the National Natural Science Founda-
tion of China (NSFC) (grant numbers 20834004 and 91027006),
the Fundamental Research Funds for the Central Universities
(2010QNA3008), the Zhejiang Provincial Natural Science Founda-
tion of China (R4100009), the MOE Key Laboratory of Macromo-
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Received: May 19, 2011
Published Online: August 2, 2011
Eur. J. Org. Chem. 2011, 5331–5335
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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