The selective dealkylations: The formylations of the three easily accessible calix[4]arene conformers immobilized by propyl and isopropyl groups

Article abstract of DOI:10.1016/j.tetlet.2012.02.061

Formyl groups were introduced to the para positions of the three easily accessible calix[4]arene conformers immobilized by four propyl or isopropyl groups by Duff reaction. Propyl group led to exhaustively formylated products due to the weak steric hinderance effect. While as for the isopropoxy calix[4]arenes, with the increase of steric hinderance, 1,3-alternate conformer gave exhaustively formylated product with no alkyl group dealkylating; partial cone conformer gave the tetraformylated proximal A,B-diether in 1,3-alternate conformation; and cone conformer led to triformylated derivatives accompanied by the selective dealkylations of three or two diametrical alkyl groups. The results indicated that the structures of the products were greatly influenced by the steric hinderance effect of the starting compounds.

Full text of DOI:10.1016/j.tetlet.2012.02.061

Tetrahedron Letters 53 (2012) 2167–2170
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Tetrahedron Letters
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The selective dealkylations: the formylations of the three easily accessible
calix[4]arene conformers immobilized by propyl and isopropyl groups
⇑
Weiping Yang, Rong Guo, Wei Wang, Shuling Gong
College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Formyl groups were introduced to the para positions of the three easily accessible calix[4]arene conform-
ers immobilized by four propyl or isopropyl groups by Duff reaction. Propyl group led to exhaustively
formylated products due to the weak steric hinderance effect. While as for the isopropoxy calix[4]arenes,
with the increase of steric hinderance, 1,3-alternate conformer gave exhaustively formylated product
with no alkyl group dealkylating; partial cone conformer gave the tetraformylated proximal A,B-diether
in 1,3-alternate conformation; and cone conformer led to triformylated derivatives accompanied by the
selective dealkylations of three or two diametrical alkyl groups. The results indicated that the structures
of the products were greatly influenced by the steric hinderance effect of the starting compounds.
Ó 2012 Elsevier Ltd. All rights reserved.
Received 28 October 2011
Revised 9 February 2012
Accepted 14 February 2012
Available online 20 February 2012
Keywords:
Selective dealkylation
Formylation
Immobilized conformation
Calixarene
6
Calixarenes which are cyclic oligomers comprising phenolic and
methylene units are ideal host compounds with a unique cavity-
shaped architecture and modifiable lower (phenol OH groups)
and upper (phenol rings) rims.1 Compared with other host com-
pounds, the conformations of calixarenes which result from the
modify the shape of the
p
-electron-rich cavity. Both of these fac-
tors may alter the surroundings of the upper rims and influence the
steric hinderance of the p-positions. Hence, in order to study the
influences of the steric hinderance effect on the functionalization
of calix[4]arenes, propyl and isopropyl groups (same type and dif-
ferent sizes) were employed to fix the conformations of
calix[4]arenes and a series of calix[4]arenes fixed in the three com-
mon conformations were synthesized as the starting compounds.
As followed, formyl groups were introduced to the para positions
of the phenol rings by using an excess of hexamethylenetetramine
(HMTA) and trifluoroacetic acid (TFA) (Duff reaction). Compared
with other formylation methods, Duff reaction is considered good
for the exhaustive formylation of calixarenes with no regio-selec-
tivity. By adopting this method, the number reduction of the
introduced formyl groups caused by other factors besides steric
hinderance can be avoided.
As shown in Schemes 1 and 2, the cone conformational calixa-
rene tetraisopropyl and tetrapropyl ethers 2 (81%) and 10 (84%) were
prepared in NaH/DMF by the reaction of 1 (de-p-tert-butylcalix[4]arene)
free rotation about the
2
r bonds of the Ar–CH –Ar groups are flex-
2
ible. For calix[4]arenes, the relative orientations of the phenol
units can in principle be assumed. Gutsche has introduced the
terms ‘cone’, ‘partial-cone’, ‘1,2-alternate’, and ‘1,3-alternate’,
3
which are generally accepted today, to these conformations.
In the calix[4]arene series, when the groups (Ppropyl) are
introduced to the lower rims, the conformations will be immobi-
lized.3 For the fixed calix[4]arene conformers, the reactive behav-
iors of the calix skeletons, especially the p-position of the phenol
rings, will be evidently influenced by the introduced groups and
their conformations. Generally, the influences of the introduced
groups are in two aspects: for the first one, different types of
groups such as alkyl, ether, and ester will affect the electronic den-
sity distribution of the phenol rings to different degrees and make
it possible to introduce functional groups to the upper rims selec-
5
b
7
with 2-iodopropane and 1-bromopropane, respectively. When the
reaction system was changed to Cs CO /acetone, 1,3-alternate
2 3
4
,5
tively; for the second one, the groups will make the lower rims
more crowded and the phenol rings will be so pinched that the ste-
ric hinderance of the p-positions of the phenol rings will be greatly
influenced. In the case of the influences of conformations on the
reactive behaviors of calix skeletons, the conformations of calixare-
nes can change the spatial orientation of the pendant groups and
8
9
tetraisopropoxy calix[4]arene 3 (52%), partial cone derivative 4
(31%), and a small amount of 1,2-alernate product 510 (2%) could
be easily isolated from the reaction. The syntheses of 11 (50%)
and 12 (34%) were similar to 3 and 4 except that the corresponding
1,2-alternate product was not obtained in this reaction.11 Formyl
groups were introduced to the para positions by Duff reaction to
7
a
12
give the derivatives 6, 7, 8a, 8b, 9, 13, 14, and 15, respectively.
Their structures were characterized by ESI-MS, H NMR, and
1
13
C
⇑
Corresponding author. Tel.: +86 27 68752701; fax: +86 27 68754067.
E-mail addresses: gongsl@whu.edu.cn, lxwhu@sohu.com (S. Gong).
1
3
NMR spectra.
0
040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2012.02.061

2
168
W. Yang et al. / Tetrahedron Letters 53 (2012) 2167–2170
Scheme 1. The formylations of different conformational calix[4]arenes immobilized by isopropyl groups.
(
(
44.45% yield of the isolated product) and a small amount of 8a
only less than 1% pure product obtained) were isolated from the
1
crude product by column chromatography. In H NMR spectrum,
compound 6 showed two singlets for the formyl protons in a ratio
of 2:1, a singlet at d 8.94 ppm (2H) arising from OH groups and two
3 2
doublets (12H) for CH(CH ) groups. Confirmed by the ESI-MS data,
compound 6 was triformylated diisopropoxy calix[4]arene. The
1
conformation of compound 6 was determined by its H NMR spec-
trum (two pairs of doublets at d 3.51 and 3.58 ppm; d 4.35 and
4
.40 ppm for methylene protons) indicating that it was present
in a cone conformation. Compound 8a was determined as tetra-
formylated diisopropoxy calix[4]arene in the cone conformation
1
by H NMR spectrum which exhibited two singlets for the formyl
protons in a ratio of 1:1 (2H, 2H), a singlet for OH groups (2H)
and a pair of doublets for methylene protons. When the reaction
was carried out for 72 h, a new compound 7 (38.21% yield of the
isolated product) and compound 8a were isolated and the yield
Scheme 2. The formylations of different conformational calix[4]arenes immobi-
lized by propyl groups.
1
The formylations of the tetraalkyl ethers were carried out by
Duff reaction. Tetrapropoxy compounds 10, 11, and 12 were
smoothly transformed into the corresponding tetraformyl deriva-
tives 13, 14, and 15 in high yields. Surprisingly, the reactions of tet-
raisopropoxy calixarenes with HMTA did not lead to the expected
but led to more complex products. After refluxing cone tetraiso-
propoxy calixarene 2 with HMTA in TFA for 24 h, compound 6
of compound 8a increased to 25.12%. The H NMR spectrum which
showed two singlets for formyl protons (2H, 1H) and one singlet
for OH groups (3H) and two pairs of doublets for methylene pro-
tons indicated that compound 7 was triformylated mono-isopro-
poxy calix[4]arene in the cone conformation.
The partial cone isomer 4 gave main product 8b in 47.75% iso-
lated yield when refluxed with HMTA in TFA for 72 h. According to

W. Yang et al. / Tetrahedron Letters 53 (2012) 2167–2170
2169
+
the ESI-MS, the [M+Na] peaks of compounds 8a and 8b were both
rings successfully. However, there were still two isopropyl groups
dealkylated. Herein, an interesting conformational behavior was
found that one of the phenol rings inverted and the conformation
transformed to 1,3-alternate. In addition, the two dealkylated iso-
propyl groups were proximal. Generally, influenced by the differ-
ent pKa1–pKa4 values of the four Ar–OH groups and
intramolecular hydrogen bonds, diametrical A,C-dialkylation is
more easily achieved than proximal A,B-dialkylation.3 Proximal
A,B-dialkylation can only be carried out by some special methods
such as direct alkylation with a strong base (e.g., NaH) or by selec-
1
at m/z 643. And the H NMR spectrum of compound 8b showed a
pair of doublets at d 3.92 and d 4.07 ppm (4H) and two singlets
2H, 2H) for the methylene protons which was different from that
of the compound 8a. In addition, the C NMR spectrum of com-
pound 8b showed three kinds of methylene C atoms. All of these
indicated that it should be one of the two proximal A,B-diethers
(
13
a
in Figure 1. As reported, the difference of chemical shift (Dd) be-
tween the high field and low field pairs of resonances of the meth-
ylene protons of the calix[4]arenes is ca. 0.9 ± 0.2 in the cone
conformation and ca. 0.5 ± 0.1 in the flattened cone conforma-
tion. Considering the low
arising from the methylene protons (
must be in 1,3-alternate conformation. According to the H NMR
data, the resonance of OH was at d 8.10 ppm which indicated the
presence of hydrogen bonds and explained why the conformation
could be immobilized at room temperature. In addition, compound
b was an inherently chiral derivative arising from the immobiliza-
tion of the conformation.
As for the formylation of 1,3-alternate isomer 3 in the same
condition, a small amount of dealkylated compound 8b (only less
than 1% pure product isolated) was obtained and the main product
was tetraformylated tetraisopropoxy calix[4]arene 9 (53.83% yield
of the isolated product) which was determined by H NMR (a sin-
glet (4H) for formyl groups and a singlet (8H) for methylene pro-
1
6
tive dealkylation with TiBr
4
.
However, the unusual formation of
3
a
D
d value between the pair of doublets
d = 0.15), compound 8b
compound 8b can be easily explained by the steric hinderance ef-
fect: with the proximal A,B-dealkylation and conformational con-
version, the two isopropyl groups were located on each side of
the cavity and the distance between them was the farthest. Fur-
thermore, the overcrowding of formyl groups at the phenol rings
was also improved. As for the 1,3-alternate isomer 3, the steric hin-
derance effect was the weakest in the three isopropoxy calix[4]ar-
ene conformers and the main product was tetraformylated with no
isopropyl group dealkylating. It was interesting that there was also
a small amount of compound 8b isolated from the crude product
and these selective dealkylations indicated that the steric hinder-
ance effect was the main driving force in the reactions although
the isopropyl group was easier to dealkylate than the propyl group.
To the best of our knowledge, besides the recent reports in thiaca-
lix[4]arene chemistry, similar connection between the conforma-
tions and the results of reaction (chemoselectivity, regioselectivity)
has not been studied systematically in classical calixarene chemis-
D
1
8
1
+
tons) and ESI-MS ([M+Na] 727).
For the tetraisopropoxy calixarenes, the steric hinderance effect
is much stronger than that of the tetrapropoxy isomers. When for-
myl groups were introduced to the formers, dealkylations were
common, while the dealkylated products were not isolated in the
formylations of tetrapropoxy isomers. The overcrowding at the
lower rims of tetraisopropoxy calixarenes can be proved by the
H NMR spectra. For the cone conformational compound 2 which
was substituted by four isopropyl groups, the lower rim was the
most overcrowded in the three isopropoxy calix[4]arene conform-
1
7
try before. Compared with isopropyl group, the steric hinderance
effect of propyl group is much weaker. So tetrapropoxy compounds
could be smoothly transformed into the corresponding tetraformyl
derivatives and no alkyl group was dealkylated.
1
The finding of selective dealkylations in Duff reaction is applica-
ble in the syntheses of calixarene derivatives. In the past, partially
substituted compounds were always employed directly as the
starting reactants in the syntheses of functionalization of partially
lower-substituted calixarenes. However, in the preparation of the
starting compounds, the reaction conditions must be controlled
carefully, and the separations were always troublesome compared
with the syntheses of tetrasubstituted calix[4]arenes.18 Most
importantly, the electronic density distribution is not equal be-
tween the substituted and unsubstituted phenol rings. Therefore,
the exhaustive functionalization of partially substituted calixarene
1
ers. The H NMR spectrum of compound 2 which was similar to
that of the known thiacalix[4]arene derivatives possessing the
cone conformation, was heavily diffused at 293 K: some character-
istic signals were not clear enough until these signals appeared
again with doubled multiplicity at lower temperatures. This indi-
cated an additional dynamic process ascribed to the pinched
cone–pinched cone interconversion between two identical con-
formers possessing lower C2v symmetry.14 Moreover, the pinched
cone structure of compound 2 was confirmed by X-ray crystallog-
5
is difficult to achieve directly. The finding of functionalization and
1
5
raphy. Therefore, when formyl groups were introduced to it in
4 h, triformylated derivative was the main product, and two iso-
dealkylation in one step can also be served in the preparation of
thiacalix[4]arene derivatives. The study of this has been in process
in our laboratory.
2
propyl groups diametrically A,C-dealkylated. As the reaction time
was prolonged, the yield of tetraformylated calix[4]arene was
slightly improved. However, the main product was still a trifomy-
lated derivative in which one more alkyl group dealkylated. It indi-
cated that the upper rim of compound 6 had been extremely
overcrowded and the introduction of the forth formyl group was
quite difficult.
Compared with the cone conformer 2, the overcrowding of par-
tial cone compound 4 was slightly better, and consequently four
formyl groups were introduced to the para positions of the phenol
In conclusion, formyl groups were introduced to the para posi-
tions of the three common calix[4]arene conformers immobilized
by propyl and isopropyl groups by Duff reaction. The steric hinder-
ance effect plays an important role in the reactions. Propyl group
led to exhaustively formylated products due to the weak steric hin-
derance effect. While as for the isopropoxy calix[4]arenes, with the
increase of steric hinderance, 1,3-alternate conformer gave exhaus-
tively formylated product with no alkyl group dealkylating; partial
cone conformer gave the tetraformylated proximal A,B-diether in
1
,3-alternate conformation; and cone conformer led to triformylat-
ed derivatives accompanied by the selective dealkylations of three
or two diametrical alkyl groups.
Acknowledgments
We are grateful to the National Natural Science Foundation of
China (20772092) and the Hubei Province Natural Science Fund
for Distinguished Young Scholars (2007ABB021) for financial
support.
Figure 1. The two possible structures of compound 8b.

2
170
W. Yang et al. / Tetrahedron Letters 53 (2012) 2167–2170
ArH), 6.79 (t, 1H, J = 7.2 Hz, ArH), 4.30–4.52 (m, 2H, OCHMe
J = 13.2 Hz, ArCH Ar), 4.35 (d, 2H, J = 13.2 Hz, ArCH Ar), 3.58 (d, 2H, J = 13.2 Hz,
ArCH Ar), 3.51 (d, 2H, J = 13.2 Hz, ArCH Ar), 1.54–1.59 (m, 12H, CH ). ESI-MS
2
), 4.40 (d, 2H,
Supplementary data
2
2
2
2
3
Supplementary data ( H NMR, 13C NMR and ESI-MS data of the
compounds) associated with this article can be found, in the online
version, at doi:10.1016/j.tetlet.2012.02.061. These data include
MOL files and InChiKeys of the most important compounds de-
scribed in this article.
1
+
m/z: 615 [M+Na] .
Compound 7: 1H NMR (CDCl
3
, 300 MHz): d 9.83 (s, 2H, CHO), 9.79 (s, 1H, CHO),
9
.77 (s, 3H, ArOH), 7.66 (s, 2H, ArH), 7.63 (s, 4H, ArH), 7.15 (d, 2H, J = 7.5 Hz,
ArH), 6.94 (t, 1H, J = 7.5 Hz, ArH), 4.56–4.68 (m, 1H, OCHMe ), 4.43 (d, 2H,
Ar), 3.69 (d, 2H, J = 14.1 Hz,
2
J = 13.2 Hz, ArCH
ArCH Ar), 3.59 (d, 2H, J = 13.2 Hz, ArCH
NMR (CDCl
2
Ar), 4.30 (d, 2H, J = 14.1 Hz, ArCH
2
13
2
2
Ar), 1.64 (d, 6H , J = 6.0 Hz, CH
3
).
C
3
, 75 MHz) : d 190.5 (CHO), 156.7, 154.3, 149.1, 133.8, 131.7, 131.2,
1
30.4, 130.2, 129.9, 128.8, 127.8, 126.3 (Ar), 80.0 (OCMe
2
), 31.8, 31.5
References and notes
À
(
ArCH
2
Ar), 21.9 (CH
3
). ESI-MS m/z: 549 [MÀH] .
1
3
Compound 8a: H NMR (CDCl , 300 MHz): d 9.84 (s, 2H, CHO), 9.69 (s, 2H,
1
.
(a) Gutsche, C. D.; Dhawan, B.; No, K. H.; Muthukrishnan, R. J. Am. Chem. Soc.
981, 103, 3782; (b) Gutsche, C. D. Acc. Chem. Res. 1983, 16, 161; (c) Van Dienst,
E.; Iwema Bakker, W.; Engbersen, J. F. J.; Verboom, W.; Reinhoudt, D. N. Pure
Appl. Chem. 1993, 65, 387; (d) Bhmer, V. Angew. Chem., Int. Ed. Engl. 1995, 34,
CHO), 8.71 (s, 2H, ArOH), 7.71 (s, 4H, ArH), 7.52 (s, 4H, ArH), 4.43–4.56 (m, 2H,
OCHMe ), 4.40 (d, 4H, J = 13.2 Hz, ArCH Ar), 3.61 (d, 4H, J = 13.2 Hz, ArCH Ar),
1.58 (d, 12H, J = 6.6 Hz, CH ). C NMR (CDCl , 75 MHz): d 190.9, 190.6 (CHO),
159.1, 155.3, 134.2, 133.5, 131.1, 131.0, 129.0, 128.0 (Ar), 80.4 (OCHMe ), 31.8
1
2
2
2
13
3
3
2
+
7
13.
(ArCH
Compound 8b: H NMR (CDCl
CHO), 8.10 (s, 2H, ArOH), 7.73 (s, 4H, ArH), 7.64 (s, 2H, ArH), 7.61 (s, 2H, ArH),
4.40-4.52 (m, 2H, OCHMe ), 4.14 (s, 2H, ArCH Ar), 4.07 (d, 2H, J = 15.3 Hz,
ArCH Ar), 3.92 (d, 2H, J = 15.3 Hz, ArCH Ar), 3.83 (s, 2H, ArCH Ar), 0.97 (d, 6H,
J = 6.0 Hz, CH ), 0.92 (d, 6H, J = 6.0 Hz, CH , 75 MHz): d 190.5,
190.3 (CHO), 157.0, 156.9, 134.5, 133.2, 132.0, 131.4, 130.3, 129.7, 128.1, 127.3
2
Ar), 22.0 (CH
3
). ESI-MS m/z: 643 [M+Na] .
1
2
3
.
.
Iwamoto, K.; Araki, K.; Shinkai, S. J. Org. Chem. 1991, 56, 4955.
(a) Gutsche, C. D. Calixarenes Revisited; Royal Society of Chemistry: Cambridge,
3
, 300 MHz): d 9.93 (s, 2H, CHO), 9.81 (s, 2H,
1
998; (b) Gutsche, C. D.; Dhawan, B.; Levine, J. A.; Hyun No, K.; Bauer, L. J.
2
2
Tetrahedron 1983, 39, 409.
2
2
2
13
4
.
.
(a) Arduini, A.; Fanni, S.; Manfredi, G.; Pochini, A.; Ungaro, R.; Sicuri, A. R.;
Ugozzoli, F. J. Org. Chem. 1995, 60, 1448; (b) Molenveld, P.; Stikvoort, W. M. G.;
Kooijman, H.; Spek, A. L.; Engbersen, J. F. J.; Reinhoudt, D. N. J. Org. Chem. 1999,
3
3 3
). C NMR (CDCl
(Ar), 74.2 (OCHMe
2
), 39.1, 34.9, 31.2 (ArCH
2
Ar), 21.4, 20.8 (CH
3
). ESI-MS m/z:
+
64, 3896.
643 [M+Na] .
5
(a) Verboom, W.; Durie, A.; Egberink, R. J. M.; Asfari, Z.; Reinhoudt, D. N. J. Org.
Chem. 1990, 55, 5639; (b) Arora, V.; Chawla, H.; Santra, A. Tetrahedron 2002, 58,
Compound 9: 1H NMR (CDCl
3
, 300 MHz): 9.69 (s, 4H, CHO), 7.53 (s, 8H, ArH),
4.42 (hept, 4H, J = 6.0 Hz OCHMe ), 3.74 (s, 8H, ArCH Ar), 1.33 (d, 24H,
, 75 MHz): d 191.5 (CHO), 159.2, 134.3, 131.4,
), 35.7 (ArCH Ar), 22.5 (CH ). ESI-MS m/z: 727
2
2
13
5
591.
3 3
J = 6.0 Hz, CH ). C NMR (CDCl
6
7
.
.
Talanova, G. G.; Talanov, V. S.; Hwang, H. S.; Park, C.; Surowiec, K.; Bartsch, R. A.
Org. Biomol. Chem. 2004, 2, 2585.
(a) Dondoni, A.; Marra, A.; Scherrmann, M. C.; Casnati, A.; Sansone, F.; Ungaro,
R. Chem. Eur. J. 1997, 3, 1774; (b) Gagnon, J.; Vezina, M.; Drouin, M.; Harvey, P.
D. Can. J. Chem. 2001, 79, 1439.
130.5 (Ar), 74.9 (OCHMe
2
2
3
+
[M+Na] .
Compound 15: 1H NMR (CDCl
, 300 MHz): d 10.00 (s, 1H, CHO), 9.99 (s, 1H,
CHO), 9.45 (s, 2H, CHO), 7.82 (s, 2H, ArH), 7.73 (s, 2H, ArH), 7.50 (s, 2H, ArH),
6.69 (s, 2H, ArH), 4.09 (d, 2H, J = 13.5 Hz, ArCH Ar), 3.92 (t, 2H, J = 7.2 Hz,
Et), 3.80 (s, 4H, ArCH Ar), 3.62–3.70 (m, 2H,
Et), 3.25 (d, 2H, J = 14.1 Hz, ArCH Ar), 2.06–
Me), 1.91–1.98 (m, 6H, CH CH Me), 1.11–1.20 (m, 9H,
). C NMR (CDCl , 75 MHz): d 191.3, 191.0
(CHO), 162.8, 162.2, 160.8, 137.1, 134.4, 134.0, 132.2, 131.5, 131.1, 130.9,
130.8, 130.4 (Ar), 76.6, 75.8, 75.5 (OCH Et), 35.1, 30.3 (ArCH Ar), 24.0, 23.7,
22.3 (CH CH Me), 10.6, 9.1 (CH ). ESI-MS m/z: 727 [M+Na] .
3
2
8
.
.
Compound 3: 1H NMR (CDCl
3
, 300 MHz): d 7.01 (d, 8H, J = 7.2 Hz, ArH), 6.61 (t,
H, J = 7.2 Hz, ArH), 4.14 (hept, 4H, J = 6.0 Hz, OCHMe ), 3.61 (s, 8H, ArCH Ar),
.21 (d, 24H, J = 6.0 Hz, CH ).
OCH
OCH
2
Et), 3.79–3.87 (m, 2H, OCH
Et), 3.23–3.30 (m, 2H, OCH
CH
), 0.62 (t, 3H, J = 7.5 Hz, CH
2
2
4
1
2
2
2
2
2
3
2.14 (m, 2H, CH
CH
2
2
2
2
1
13
9
Compound 4: H NMR (CDCl
3
, 300 MHz): d 7.17 (d, 2H, J = 7.8 Hz, ArH), 7.08 (d,
H, J = 7.5 Hz, ArH), 6.97 (d, 2H, J = 7.5 Hz, ArH), 6.91 (t, 1H, J = 7.2 Hz, ArH),
.78 (t, 1H, J = 7.2 Hz, ArH), 6.40 (t, 2H, J = 7.5 Hz, ArH), 6.18 (d, 2H, J = 7.2 Hz,
), 4.14 (d, 2H, J = 12.6 Hz, ArCH Ar),
), 3.70 (s, 4H, ArCH Ar), 2.98 (d, 2H, J = 13.2 Hz,
Ar), 1.28–1.34 (m, 18H, CH ), 0.94 (d, 6H, J = 6.0 Hz, CH ).
, 300 MHz): d 7.06 (d, 4H, J = 7.8 Hz, ArH), 7.02 (d,
H, J = 7.5 Hz, ArH), 6.80 (t, 4H, J = 7.5 Hz, ArH), 4.32 (d, 2H, J = 12.6 Hz,
ArCH Ar), 3.90 (s, 4H, ArCH Ar), 3.83 (hept, 4H, J = 6.0 Hz, OCHMe2), 3.09 (d,
H, J = 12.6 Hz ArCH Ar), 0.93 (d, 12H, J = 5.7 Hz, CH3), 0.64 (d, 12H, J = 6.0 Hz,
CH ).
3
3
3
2
6
2
2
+
ArH), 4.30 (hept, 1H, J = 6.0 Hz, OCHMe
.91–4.07 (m, 3H, OCHMe
ArCH
0. Compound 5: H NMR (CDCl
2
2
2
2
3
3
2
2
14. (a) Himl, M.; Pojarova, M.; Stibor, I.; Skora, J.; Lhotak, P. Tetrahedron Lett. 2005,
46, 461; (b) Cajan, M.; Lhotak, P.; Lang, J.; Dvorakova, H.; Stibor, I.; Koca, J. J.
Chem. Soc., Perkin Trans. 2 2002, 1922; (c) Lhotak, P.; Himl, M.; Stibor, I.; Sykora,
J.; Dvorakova, H.; Lang, J.; Petrickova, H. Tetrahedron 2003, 59, 7581.
15. Chester, R.; De Marco, R.; Mocerino, M.; Ogden, M.; Skelton, B.; White, A.
Supramol. Chem. 2009, 21, 479.
16. (a) Brunink, J. A. J.; Verboom, W.; Engbersen, J. F. J.; Harkema, S.; Reinhoudt, D.
N. Recl. Trav. Chim. Pays-Bas. 1992, 111, 511; (b) Pappalardo, S. New. J. Chem.
1996, 20, 465; (c) Groenen, L. C.; Ruël, B. H. M.; Casnati, A.; Timmerman, P.;
Verboom, W.; Harkema, S.; Pochini, A.; Ungaro, R.; Reinhoudt, D. N. Tetrahedron
Lett. 1991, 12, 2675; (d) Arduini, A.; Casnati, A.; Dodi, L.; Pochini, A.; Ungaro, R.
J. Chem. Soc., Chem. Commun. 1990, 1597.
17. (a) Desroches, C.; Kessler, V. G.; Parola, S. Tetrahedron Lett. 2004, 45, 6329; (b)
Kundrat, O.; Cisarova, I.; Böhm, B.; Pojarova, M.; Lhoták, P. J. Org. Chem. 2009,
74, 4592; (c) Kundrat, O.; Dvorakova, H.; Cisarova, I.; Pojarova, M.; Lhoták, P.
Org. Lett. 2009, 11, 4188; (d) Kundrat, O.; Dvorakova, H.; Eigner, V.; Lhoták, P. J.
Org. Chem. 2010, 75, 407.
2
3
3
1
1
3
4
2
2
2
2
3
1
1
1
1. Iwamoto, K.; Shinkai, S. J. Org. Chem. 1992, 57, 7066.
2. Lhotak, P.; Shinkai, S. Tetrahedron Lett. 1996, 37, 645.
3. Preparation of 6 and 8a: A mixture of calixarene 2 (0.45 g, 0.76 mmol),
hexamethylenetetramine (3.84 g, 20.19 mmol), and trifluoroacetic acid
(
3
20 mL) was stirred at 100 °C for 24 h. Then the mixture was poured into
0 mL of ice-water and extracted with chloroform. The chloroform solution
was washed with water and dried over MgSO and then filtered and
4
,
concentrated under vacuum. The residue was purified by column
chromatography to give 6 and 8a.
The procedures of preparing 7, 9, 8b, 13, 14, and 15 were similar to 6 except
that the reaction time was 72 h.
18. (a) Lhoták, P.; Bílá, A.; Budka, J.; Pojarová, M.; Stibor, I. Chem. Commun. 2008,
1662; (b) Bitter, I.; Csokai, V. Tetrahedron Lett. 2003, 44, 2261.
Compound 6: 1H NMR (CDCl
8
, 300 MHz): d 9.81 (s, 2H, CHO), 9.71 (s, 1H, CHO),
.94 (s, 2H, ArOH), 7.66 (s, 4H, ArH), 7.52 (s, 2H, ArH), 6.98 (d, 2H, J = 7.2 Hz,
3