From rotaxanes to knots. Templating, hydrogen bond patterns, and
cyclochirality*
Carin Reuter, Roland Schmieder, and Fritz Vögtle
Kekulé-Institut für Organische Chemie und Biochemie der
Universität Bonn, Gerhard-Domagk-Str. 1, D-53121 Bonn, Germany
Abstract: Rotaxanes of the amide type have been accessible in
preparative yields by a variety of reactions. Beneath SN2- and SN2t-mechanisms
we developed a synthesis of [2]rotaxanes that comes off a Michael addition.
The motif of the attractive interactions between an axle-shaped and
a macrocyclic wheel part to form rotaxanes consists of multiple hydrogen
bonds in the nonionic strategy (threading), as well as in a new high
yield anionic template synthesis (trapping). We introduce new synthetic
routes for the preparation of [n]rotaxanes using nonionic as well as
anionic templates. Furthermore, we report on the latest results of the
statistical synthesis (slipping) by melting together axle and wheel
to form rotaxanes. The chiroptical properties of a homologous series
of cycloenantiomeric [1]rotaxanes as well as a cyclodiastereomeric [3]rotaxane
have been described. The differences in the Cotton effects obtained
show that small structural changes have an impact on the chiroptical
properties of rotaxanes. The first X-ray structures obtained of cycloenantiomerically
chiral amide-based [2]- and [1]rotaxanes as well as of the first topologically
chiral amide-based knot compound were solved which show networks of
H-bonds between the entities of the rotaxanes and the segments of the
knot-shaped molecule. Our investigations in template effects based on
hydrogen bonding for the synthesis of supramolecular structures open
up a variety of strategies for the preparation of catenanes, rotaxanes
andrecentlyeven molecular knots.
*Plenary lecture presented at the 15th
International Conference on Physical Organic Chemistry (ICPOC 15), Göteborg,
Sweden, 8 13 July 2000. Other presentations are published in this
issue, pp. 2219 2358.
**Corresponding author
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