Pj. Skinner et al., Conformational switching of resorcin[4]arene cavitands by protonation - Preliminary communication, HELV CHIM A, 84(7), 2001, pp. 2146-2153
The synthesis of the quinoxaline-bridged resorcin[4]arene cavitand I was ac
complished from 2-[3,5-di(tertbutyl)phenyl]acetaldehyde via formation of th
e intermediate octol 2. Such cavitands are known to occur in an open 'kite'
conformation at low temperature (< 213 K) but to adopt it 'vase' conformat
ion at elevated temperatures (> 318 K). We discovered that protonation of c
avitand I at room temperature by common acids, such as CF3COOH, also causes
reversible switching from 'vase' to 'kite'. and that this conformational c
hange can be conveniently monitored by both H-1-NMR and UV/VIS spectroscopy
.