Anions are important hydrogen bond acceptors in
a range of biological, chemical, environmental and medical molecular
recognition processes.<sup> </sup>These interactions have been exploited for
the design and synthesis of ditopic resorcinarenes as the hydrogen bond strength
can be tuned through the modification of the substituent at the 2-position.
However, many potentially useful compounds, especially those incorporating
electron-withdrawing functionalities, have not been prepared due to the
challenge of their synthesis: their incorporation slows resorcinarene formation
that is accessed by electrophic aromatic substitution. As part of our broader
campaign to employ resorcinarenes as selective recognition elements, we need
access to these specialized materials, and in this article we report a straightforward
synthetic pathway for obtaining a 2-(carboxymethyl)-resorcinarene, and
resorcinarene esters in general. We discuss the unusual conformation it adopts,
and propose that this arises from the electron-withdrawing nature of the ester
substituents that renders them better hydrogen bond acceptors than the phenols,
ensuring that each of those acts as a donor only. DFT calculations show that
this conformation arises as a consequence of the unusual configurational
isomerism of this compound and interruption of the archetypal hydrogen bonding
by the ester functionality.
Selective recognition of small hydrogen bond acceptors by a calix[6]arene-based molecular container
