Scott, Michael P.
Description
The work described in this thesis is focused on the synthesis,
functionalisation and study of conformationally restricted
cavitand systems. Cavitands are rigid molecules with a concave
π-basic surface, which bind a variety of guests. Larger
supramolecular systems have been synthesised by covalently
connecting several cavitands together. Two such multi-cavitand
arrays are presented in this thesis, namely superbowls and
cyclotetra-cavitands.
Chapter...[Show more] 1 is a review of resorcinarenes and pyrogallolarenes. The
configurational and conformational possibilities of these
molecules is discussed, along with the various synthetic methods
developed for their preparation and derivatisation. The reported
types of hydrogen-bonded, metal coordinated and covalently-linked
multi-resorcinarene and multi-pyrogallolarene structures are
described. The host-guest chemistry of these structures is
described, as is their use as a catalyst for chemical
transformations.
Chapter 2 is an introduction to the chemistry of superbowls and
related deep-cavity cavitands. The synthesis of superbowls by the
reaction of four ‘wall’ cavitands with one ‘base’
cavitand is described, followed by the methods developed for
their derivatisation. The ability of superbowls to act as hosts
to tetra-alkyl ammonium salts and aspirin is discussed. Finally,
the chemistry of deep-cavity cavitands with introverted
functionality is surveyed.
Chapter 3 describes the synthesis of new ortho-functionalised,
arylated cavitands. These arylated cavitands exist as two
atropisomers due to restricted rotation of the biaryl bond. The
two atropisomers are described as either ‘inside’ or
‘outside’, depending on whether the ortho-functionality
resides inside or outside of the cavity of the cavitand. Methods
for the synthesis and interconversion of these two atropisomers
are investigated. By varying the temperature and solvent, either
the inside or outside atropisomer could be made the predominant
species in solution. The addition of acids to the solution of a
cavitand with an amine substituent resulted in significant
changes to atropisomer equilibrium ratios.
Chapter 4 describes the synthesis of new superbowls by a novel
synthetic route. This route first combines one functionalised
‘wall’ cavitand with the ‘base’ cavitand, followed by the
incorporation of three unfunctionalised wall cavitands. This
novel approach permits the synthesis of sizeable amounts of
previously difficult-to-obtain mono-functionalised superbowls.
The first superbowl with introverted functionality is reported. A
preliminary study of this superbowl’s inside/outside
atropisomerism and host-guest chemistry is described.
Chapter 5 describes how cavitand bowls carrying two
distally-positioned terminal alkyne substituents generate
cyclotetramers from Glaser coupling reactions. The
1,3-butadiynyl-linked cyclotetra-cavitand exists predominantly in
two equivalent saddle shaped conformations. Interchange is rapid
on the human timescale at ambient temperature but is modulated
through manipulation of bowl rim substituents. Conversion of the
four 1,3-butadiynyl-linkers into 2,5-thiophenylene-linkers causes
a switch to a square-shaped cyclotetra-cavitand with the four
sulfurs directed outside of the newly-formed macrocycle.
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