The novel title macrocycles, based
on methylene-bridged 1,5-naphthalene
units, have been obtained by template effect in a thermodynamically
controlled synthesis. In detail, the prism[5]arene
1
or
the prism[6]arene
3
was selectively removed from the
equilibrium mixture by using the complementary ammonium-templating
agent. When only the solvent 1,2-DCE was used, the 1,4-confused derivative
2
was obtained. The prism[5]arene here described shows a deep
π-electron-rich aromatic cavity that exhibits a great affinity
for the quaternary ammonium guests, originating from favorable cation···π
and
+
NC–H···π interactions.
This recognition motif is the basis of the templated synthesis of
the prism[
n
]arenes here reported.
A novel catalytic feature of a hexameric resorcinarene capsule is highlighted. The self-assembled cage was exploited to promote the Friedel-Crafts benzylation of several arenes and heteroarenes with benzyl chloride under mild conditions. Calculations showed that there are catalytically relevant hydrogen-bonding interactions between the bridging water molecules of the capsule and benzyl chloride, which is fundamental for the activation of the C-Cl bond. The capsule controls the reaction outcome. Inside the inner cavity of the capsule, N-methylpyrrole is preferentially benzylated in the unusual β-position while mesitylene reacts faster than 1,3-dimethoxybenzene despite the greater π-nucleophilicity of the latter compound.
The absolute configuration of antiinflammatory marine sesterterpenes belonging to the manoalide and cacospongionolide structural type has been determined by comparison of the CD spectra of the natural compounds with those of analogues that have been stereoselectively synthesized. In the derived acetates the relative stereochemistry of the stereogenic centres in the pyranofuranone moiety is assigned from 1H‐NMR data and the absolute configuration from CD spectra. The absolute configuration of the naturally occurring marine sesterterpenes thorectolide monoacetate, manoalide monoacetate, petrosaspongiolide M and cavernosolide has been determined.
The hexameric resorcinarene capsule reported by Atwood in 1997 is able to act as a supramolecular catalyst. Its inner cavity provides a unique environment, in which organic reactions can be efficiently catalyzed, thanks to the confinement effect of the substrates. In addition, different stereo‐ and regiochemical outcomes can be observed with respect to reactions in the bulk solvent. The hexameric capsule shows some catalytic features reminiscent of natural enzymes. In particular, highlights of the capsule discussed herein include 1) its ability to recognize the substrates (substrate selectivity), 2) the possibility of stabilizing the transition states and intermediates through secondary interactions, 3) an inherent Brønsted acidity, and 4) its ability to act as a hydrogen‐bond catalyst. In addition, it is also shown how the catalytic activity of the hexameric capsule can be modulated in the presence of competitive alkylammonium guests, which show high affinities for its internal cavity. These aspects are discussed through a critical examination of data reported in the literature in recent years.
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