The synthesis of the quinoxaline-bridged resorcin[4]arene cavitand 1 was accomplished from 2-[3,5-di(tert-butyl)phenyl]acetaldehyde via formation of the intermediate octol 2. Such cavitands are known to occur in an open `kite' conformation at low temperature (<213 K) but to adopt a `vase' conformation at elevated temperatures (>318 K). We discovered that protonation of cavitand 1 at room temperature by common acids, such as CF3COOH, also causes reversible switching from `vase' to `kite', and that this conformational change can be conveniently monitored by both 1H-NMR and UV/VIS spectroscopy.
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Skinner et al. (2001) studied this question.