ORGANIC
LETTERS
2009
Vol. 11, No. 18
4184-4187
Glycoluril Trimers: Selective Synthesis
and Supramolecular Properties
Marek Stancl, Martin Hodan, and Vladimir Sindelar*
Department of Chemistry, Masaryk UniVersity, Kotlarska 2, 611 37 Brno, Czech Republic
Received August 3, 2009
ABSTRACT
The first selective synthesis of glycoluril trimers is described. Trimers framed by o-xylylene walls represent new supramolecular hosts which
are able to encapsulate bispyridinium ethylene and methylviologen guests in the solid state and aqueous solution.
Glycoluril and its derivatives are rigid heterocycles which
are used as building blocks for the construction of various
supramolecular objects. Glycolurils that are terminated by
two xylylene units and contain a bulky substituent on their
convex face are known to behave as molecular clips.1 The
connection of glycoluril units with aromatic spacers also
leads to molecules which can self-assemble into pseudo-
spherical structures.2 Among these supramolecular objects,
the most attention has been paid to the macrocyclic molecules
known as cucurbit[n]urils (CBn).3 These macrocycles are
prepared by the polycondensation reaction between glycoluril
and formaldehyde in mineral acid. With the exception of
CB6, which can be readily prepared in conc. H2SO4 and
temperatures above 100 °C as the sole macrocyclic product,3c
mixtures of CBn homologues are obtained under milder
reaction conditions, and difficult separation is required to
obtain a unique macrocycle.3e Recently it was also demon-
strated that the choice of a suitable formaldehyde/glycoluril
ratio, reaction time, and other reaction conditions allows for
the preparation of CB analogues as diastereomeric inverted
CB[n],4 bis-ns-CB[10],5 and/or (()-bis-ns-CB[6].6 Using the
same approach, Isaacs group has been able to isolate not
only a previously described glycoluril dimer7 but also higher
acyclic oligomers with a number of glycoluril units ranging
from 2 to 6.6,8 They also demonstrated the ability of
pentamers and hexamers to bind organic guests bearing
positive charge. Inspired by these studies, we decided to
investigate the possibility of creating a stepwise approach
for the synthesis and characterization of glycoluril oligomers.
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(b) Sijbesma, R. P.; Nolte, R. J. M. Top. Curr. Chem. 1995, 175, 25–56.
(c) Rowan, A. E.; Elemans, J. A. A. W.; Nolte, R. J. M. Acc. Chem. Res.
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Ind. Eng. Chem. Res. 2000, 39, 3419–3428. (e) Wang, Z.-G.; Zhou, B.-H.;
Chen, Y.-F.; Yin, G.-D.; Li, Y.-T.; Wu, A.-X.; Isaacs, L. J. Org. Chem.
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Fettinger, J. C.; Isaacs, L. J. Org. Chem. 2003, 68, 6184–6191.
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(3) (a) Lee, J. W.; Samal, S.; Selvapalam, N.; Kim, H.-J.; Kim, K. Acc.
Chem. Res. 2003, 36, 621–630. (b) Lagona, J.; Mukhopadhyay, P.;
Chakrabarti, S.; Isaacs, L. Angew. Chem., Int. Ed. 2005, 44, 4844–4870.
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Hu, M.; Xiao, H.; Day, A. I. Chin. Sci. Bull. 2004, 49, 1111–1116.
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10.1021/ol9017886 CCC: $40.75
Published on Web 08/25/2009
2009 American Chemical Society