Synthesis and characterization of p-tert-butylcalix[6]-1,4-crown-4-2,6-crown-5, p-tert-butylcalix[6]-1,4-benzocrown-4-2,3-crown-5

Article abstract of DOI:10.1246/cl.2000.1208

Two new types of calix[6]-bis-crowns, p-tert-butylcalix[6]-1,4-crown-4-2,6-crown-5 and p-tert-butylcalix[6]-1,4-benzo-crown-4-2,3-crown-5, have been synthesized and characterized. The conformation of p-tert-butylcalix[6]-1,4-crown-4-2,6-crown-5 may be (u,

Full text of DOI:10.1246/cl.2000.1208

1208
Chemistry Letters 2000
Synthesis and Characterization of p-tert-Butylcalix[6]-1,4-crown-4-2,6-crown-5,
p-tert-Butylcalix[6]-1,4-benzocrown-4-2,3-crown-5
Yuan-Yin Chen* and Hai-Bing Li
Department of Chemistry, Wuhan University, Wuhan 430072, P. R. China
(Received July 10, 2000; CL-000659)
Two new types of calix[6]-bis-crowns, p-tert-butylcalix[6]-
treated with HCl(10%, v/v) and then extracted with ethyl
acetate. After purification by column chromatography, p-tert-
butylcalix[6]-1,4-crown-4-2,6-crown-5 2a and p-tert-butyl-
calix[6]-1,4-benzocrown-4-2,3-crown-5 2b were isolated as
white solids in 32% yield, mp 314-316 °C and in 46% yield, mp
283–285 °C, respectively.
1,4-crown-4-2,6-crown-5 and p-tert-butylcalix[6]-1,4-benzo-
crown-4-2,3-crown-5, have been synthesized and characterized.
The conformation of p-tert-butylcalix[6]-1,4-crown-4-2,6-
crown-5 may be (u,d,d,u,d,d) or (u,d,u,u,u,d), and can not be
further assigned, the latter adopts (u,u,u,u,u,u) conformation at
room temperature.
Calixcrowns are a family of calixarenes in which the phe-
nolic oxygens are linked via flexible poly(oxyethylene) chains
intramolecularly. As they possess well preorganized structures
and more rigid binding sites in comparison with calixarenes and
crown ethers, they exhibited superior recognition ability toward
alkali metal ions and other ions by the co-operation effect of
calixarene and crown moieties. For example, the Na+/K+ selec-
tivity attainable with crown ethers has been saturated at the 102
order, with calixarenes the selectivity can reach 103.1, but it is
105.3 for diethoxycalix[4]crown-4 in a partial cone conforma-
tion.1 And also, calix[4]arene crown-6 hosts have been investi-
gated in the sequestration and removal of radioactive 137Cs from
aqueous waste mixtures.2 Therefore, much attention has been
paid to the more sophisticated molecules: calix-bis-crowns. All
possible types of calix[4]-bis-crowns have been synthesized,3–9
and their recognition properties toward Cs+, K+ etc. have been
studied.10–14 However, in contrast to the extensive investigation
on calix[4]-bis-crowns, nothing is known about calix[6]-bis-
crowns until we synthesized the first calix[6]-bis-crown, p-tert-
butylcalix[6]-1,4-2,5-bis-crown–4s15 and meanwhile, Blanda et
al. reported another example of calix[6]-bis-crowns, 1,4-dially-
loxy-calix[6]-2,6-3,5-bis-crown-4s.16 There are eight possible
positional isomers of calix[6]-bis-crowns. Thus, only a small
part of calix[6]-bis-crowns have been synthesized.
In this paper, we wish to report the synthesis and character-
ization of two new types of calix[6]-bis-crowns, p-tert-butyl-
calix[6]-1,4-crown-4-2,6-crown-5 2a and p-tert-butyl-calix-[6]-
1,4-benzocrown-4-2,3-crown-5 2b. The new calix[6]-bis-
crowns are also the first examples of calix[6]-bis-crowns with
inequivalent crown loops in length. Their extraction behavior
towards some picrate salts was also investigated. The synthetic
route is depicted as Scheme 1:
Reacting p-tert-butyl-calix[6]arene with triethylene glycol
ditosylates or 1,2-bistosyloxyethoxybenzene in the presence of
9 equivs of K2CO3 in toluene for 24 h under a nitrogen atmos-
phere, 1,4-p-tert-butylcalix[6]crown-4 1a and 1,4-p-tert-butyl-
calix [6]benzocrown-4 1b were obtained in 40 and 55% yield,
respectively.15 To the DMF solution of 1, NaH was added at
room temperature, followed by 1.2 equivs of tetraethylene gly-
col ditosylates with stirring at 60 °C for 12 h. The excess of
NaH was quenched by addition of a minimal quantity of
methanol (caution!). Distilling off the solvent, the residue was
Two compounds gave satisfactory elemental analysis
results and exhibited the expected molecular ion peaks. The
structures of these compounds were also confirmed by NMR
spectra.18 In the NMR spectrum of 2a, four singlets for the tert-
butyl groups (1:2:2:1), three pairs of doublets (one is mixed
with ethylene protons) (1:1:1) for methylene protons and a sin-
glet for hydroxyl protons can be assigned. This is in good
accordance with the structure of p-tert-butylcalix[6]-1,4-crown-
4-2,6-crown-5 2a and not in accordance with other structures
such as p-tert-butylcalix[6]-1,4-crown-4-2,5-crown-5 or p-tert-
butylcalix[6]-1,4-crown-4-2,3-crown-5, which should have
three singlets for the tert-butyl groups (1:1:1). However, as the
(u,d,d,u,d,d) 2a’ and (u,d,u,u,u,d) 2a” conformations will give
similar NMR data for methylene protons, it is not possible to
further assigned, although we believe that the former is more
plausible. In the NMR spectrum of 2b, three singlets for the p-
tert-butyl groups (1:1:1), four pairs of doublets (one is mixed
with ethylene protons) (1:2:2:1) for methylene protons, a singlet
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1209
for hydroxyl protons can be assigned. This is consistent with
the structure of p-tert-butylcalix[6]-1,4-benzocrown-4-2,3-
crown-5 and not with other structures such as p-tert-butylcal-
ix[6]-1,4-benzocrown-4-2,6-crown-5, which should have four
singlets for p-tert-butyl (1:2:2:1) or p-tert-butylcalix[6]-1,4-
benzocrown-4-2,5-crown-5 which should have three pairs dou-
blets (1:1:1) for methylene protons. The cone (u,u,u,u,u,u)
conformation of 2b at room temperature is easily deduced from
the methylene protons in calixarene skeleton showing four
pairs of doublets in a ratio of 1:2:2:1.
Examination of the CPK molecular models reveals that
compounds 2a, 2b are well preorganized for binding cations.
1,4-p-tert-Butylcalix[6]crown-4 1a and 1,4-p-tert-butylcalix-
[6]-benzocrown-4 1b are used as reference compounds.
Percentage extraction of hosts 2a, 2b towards several picrate
salts from water into CHCl3 at 25 °C are summarized in Table
1. Comparing with compounds 1a and 1b, the extraction level
of p-tert-butylcalix[6]-1,4-benzocrown-4-2,3-crown-5 (2b) is
much higher, this can be attributed to the beneficial influence of
a second bridging subunit generally increases the rigidity of
calix[6]arene framework and compound 2b adopts a cone con-
formation at the room temperature. Besides, the seletivity
towards the alkali metal ions for compounds 2a and 2b is also
different for that of compounds 1a and 1b. This may be attrib-
uted to two polyethylene glycol chains co-operation effect.
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18 1H NMR ( 300 MHz, CDCl3): 2a.1.17(s, 9H, C(CH3)3),
1.24(s, 18H, C(CH3)3), 1.26(s, 18H, C(CH3)3), 1.32(s, 9H,
C(CH3) 3), 2.35(t, 4H, J = 9.0 Hz, OCH2CH2), 2.70(d, 2H,
J = 10.8 Hz, OCH2CH2), 2.88(q, 4H, J = 10.5 Hz,
COCH2CH2), 3.16(q, 4H, J = 10.5 Hz, OCH2CH2), 3.31(t,
4H, J = 9.0 Hz, OCH2CH2), 3.44(d, 2H, J = 10.2Hz,
ArCH2Ar), 3.53–3.64(m, 12H, OCH2CH2 and ArCH2Ar),
3.87(d, 2H, J = 10.2 Hz, ArCH2Ar), 4.08(d, 2H, J = 13.5
Hz, ArCH2Ar), 4.17(d, 2H, J = 13.5 Hz, ArCH2Ar), 4.47(d,
2H, J = 17.7 Hz, ArCH2Ar), 6.54(d, 2H, J = 2.7 Hz, ArH),
6.72 (d, 4H, J = 2.7 Hz, ArH), 6.95(d, 4H, J = 2.7 Hz,
ArH), 7.14(s, 2H, ArOH), 7.34(d, 2H, J = 2.7 Hz, ArH).
MS(FAB): 1,244 (M+, 20%). Anal. Calcd for C80H108O11:
C, 77.13; H, 8.74%. Found: C, 77.15; H, 8.71%.
2b. 1.16(s, 18H, C(CH3)3), 1.22(s, 18H, C(CH3)3), 1.26(s,
18H, C(CH3)3), 2.44(t, 2H, J = 9.0 Hz, OCH2CH2), 2.73(q,
4H, J = 10.2 Hz, OCH2CH2), 2.92(q, 4H, J = 10.2 Hz,
OCH2CH2), 3.11(t, 4H, J = 9.0 Hz, OCH2CH2), 3.26-
3.59(m, 11H, OCH2CH2 and ArCH2Ar), 3.82(d, 1H, J =
10.2 Hz, ArCH2Ar), 3.90(d, 1H, J = 10.2 Hz, ArCH2Ar),
4.03(d, 2H, J = 17.4 Hz, ArCH2Ar), 4.14(d, 2H, J = 13.8
Hz, ArCH2Ar), 4.19(d, 1H, J = 12.9 Hz, ArCH2Ar), 4.34(d,
2H, J = 13.8 Hz, ArCH2Ar), 4.43(d, 2H, J = 17.4 Hz,
ArCH2Ar), 6.44(s, 4H, ArH), 6.62(d, 4H, J = 2.7 Hz),
7.05(d, 4H, J = 2.7 Hz, ArH), 7.36(d, 4H, J = 2.7 Hz,
ArH), 8.15(s, 2H, ArOH). MS(FAB): 1,293 (MH+, 10%).
Anal. Calcd for C84H108O11: C, 77.98;H, 8.41%. Found: C,
77.95; H,8.45%.
Financial support from the Natural Science Foundation of
China is gratefully acknowledged.
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