Scheme 1 Calix[n]arene templated synthesis of thiacalix[n]arenes.
the reaction. Though 5n were detected in the reaction mixture, carcerand type structure, and thus, this approach can be
it was not possible to isolate them, and hence a better method
was required for sulfurization. An already known sulfurization
technique is the one using SCl2 (D in Scheme 1), which
incidentally was used for the first synthesis of 14 in a step-wise
manner.7 In present case, sulfurization of 4n with SCl2 gave
excellent results in all the cases, and CnA–TCnA pseudo
dimers 5n were obtained in good yields.8 The 1H NMR spectra
of all variants 54–8 showed similar unrestrained structures.9
The final step to achieve the TCnA derivatives was exhaus-
tive halo-dealkoxylation10 of 5n in aqueous ethanol using
LiI, to cleave the ether linkages between two macrocycles
(1n and 2n), followed by their chromatographic separation or
fractional crystallization (based on differential solubility). As
can be inferred from the data listed in Table 1, all TCnA
variants have been achieved in very good yields, and though
being a multi-step synthesis, satisfactory overall yields promise
its application on relatively larger scales. Further, the CnA
templates may be recuperated with high overall % recovery
ranging from ca. 60–75%.
employed to produce some more exciting carcerands as well.
In conclusion, an alternative approach to synthesize higher
heteracalixarenes, in particular thiacalixarenes, has been
developed and demonstrated successfully. Further, the carcer-
and like intermediates (pseudo-dimers) achieved in this fash-
ion have dimensions on the nano scale, and are promising
candidates for supramolecular nano-tubes, which will be
further explored in due course to fulfil a variety of purposes
already described in the nano-sciences.
We are grateful to the University Grant Commission (UGC,
New Delhi) for providing a senior research fellowship (SRF)
to M. H. Patel.
Notes and references
1 Z. Asfari, V. Bohmer, J. Harrowfield and J. Vicens, in Calix-
arenes 2001, Kluwer Academic, Dordrecht, 2001; for recent re-
views on thiacalixarenes see: N. Morohashi, F. Narumi, N. Iki,
T. Hattori and S. Miyano, Chem. Rev., 2006, 106, 5291; P. Lhotak,
Eur. J. Org. Chem., 2004, 1675.
The present strategy, viz. pre-organization of individual
aromatic units with the help of other similar assembly and
subsequent cyclization to produce pseudo dimers, is modular in
the sense that it can be applied to synthesize other supra-
molecular assemblies of the calix family in numerous ways.11
For instance, the strategy can be extended (a) to prepare various
heteracalixarenes, with hetero-atom bridges other than sulfur,
by employing different reagents for cyclization of appended
phenol units, (b) to synthesize TCnA derivatives with various
para-substitutions (for which cyclization is not possible via
direct sulfurization), as long as they are sufficiently activating
to permit meta-substitution. It may be noticed that 5 possesses a
2 M. Patel, V. Patel and P. Shrivastav, Tetrahedron Lett., 2008, 64,
3087.
3 H. Kumagai, M. Hasegawa, S. Miyanari, Y. Sugawa, Y. Sato,
T. Hori, S. Ueda, H. Kamiyama and S. Miyano, Tetrahedron Lett.,
1997, 38, 3971.
4 N. Kon, N. Iki and S. Miyano, Tetrahedron Lett., 2002, 43, 2231;
N. Iki, C. Kabuto, T. Fukushima, H. Kumagai, H. Takeya,
S. Miyanari, T. Miyashi and S. Miyano, Tetrahedron, 2000, 56,
1437; S. Shokova, V. Tafeenko and V. Kovalev, Tetrahedron Lett.,
2002, 43, 5153; P. Lhotak, T. Smejkal, I. Stibor, J. Havlicek,
M. Tkadlecova and H. Petrıckova, Tetrahedron Lett., 2003, 44,
8093; Y. Kondo, K. Endo, N. Iki, S. Miyano and F. Hamada,
J. Inclusion Phenom. Macrocycl. Chem., 2005, 52, 45; Y. Kondo and
F. Hamada, J. Inclusion Phenom. Macrocycl. Chem., 2007, 58, 123.
5 M. Patel and P. S. Shrivastav, J. Inclusion Phenom. Macrocycl.
Chem., DOI: 10.1007/s10847-006-9520-7.
6 J. Lang, J. Vagherova, J. Czernec and P. Lhotak, Supramol. Chem.,
2006, 18, 371.
7 T. Sone, Y. Ohba, K. Moriya, H. Kumada and K. Ito, Tetra-
hedron, 1997, 53, 10689.
Table
Scheme 1)
1
%yields of products (Xn) in individual steps (as per
Intermediates/products (X)
8 Compound 54 has already been prepared by reacting tetra-
((2-tosyl)-ethyl)ether of calix[4]arene with thiacalix[4]arene.
Conformational preferences of various 54 derivatives and their
comparative study with bis(calix[4]arenes) has also been reported.
E. Khomich, M. Kashapov, I. Vatsuro, E. Shokova and
B. Kovalev, Russ. J. Org. Chem., 2007, 43, 192.
9 The work of Beer et al. may be of particular interest for study
of conformational analysis of bis(calix[4]arene) tubes and their
various derivatives, by NMR spectroscopy as well as X-ray
diffraction. P. Schmitt, P. Beer, G. Michael and P. Sheen, Angew.
Chem., Int. Ed., 1997, 36, 1840; S. Matthews, P. Schmitt, V. Felix,
3a
4 (A/B)a,b
5
1
n
4
5
6
7
8
86
42
—
—
—
76/82
70/78
—/70
—/59
—/37
62
58
57
54
32
85
84
79
73
64
a
b
Isolated yields of cone conformer only. According to Routes A and B.
ꢀc
This journal is The Royal Society of Chemistry 2009
Chem. Commun., 2009, 586–588 | 587