H. Takemura et al., SYNTHESIS AND PROPERTIES OF N-SUBSTITUTED AZACALIX[N]ARENES, Journal of inclusion phenomena and molecular recognition in chemistry, 19(1-4), 1994, pp. 193-206
Side arm modifications of hexahomotriazacalix[3]arene (1) were achieve
d by simple synthetic methods. Compound 5 has picolyl side arms and li
quid-liquid extraction experiments showed that the alkali cation affin
ity of 5 is much stronger than that of 1. A chiral group was also intr
oduced into the azacalixarene structure. Calix[4]arene was converted i
nto dihomoazacalix[4] arene (2) in 8% yield. Clathrate formation of 2
with various solvents is described. MM3 calculations were carried out
on p-substituted analogs of 2. The 'self-filled' structure, in which t
he benzyl side arm is placed in its cavity, is the most stable structu
re when the p-positions of the aromatic rings carry small substituents
. Strong hydrogen bonds between nitrogen and phenolic hydroxyl groups
in dihomoazacalix[4]arene (2) were observed at low temperatures. The H
-1-NMR signals of phenolic hydroxyl groups appeared as six singlets in
the range of 9.8 similar to 17.1 ppm at -70 degrees C.