T. Yamato et al., PREPARATION AND CONFORMATIONAL STUDIES OF ETHYLENE-BRIDGED CALIXARENE-ANALOGOUS MACROCYCLIC METACYCLOPHANES, Chemische Berichte, 126(11), 1993, pp. 2501-2504
The novel macrocyclic compounds hexahydroxy[2.1.2.1.2.1]-(7b) and octa
hydroxy[2.1.2.1.2.1.2.1]metacyclophane (7c) have been prepared from an
isole in six steps by using the tert-butyl function as a positional pr
otective group on the aromatic ring. Base-catalyzed condensation of 1,
2-bis(5-tert-butyl-2-hydroxyphenyl)ethane (5) with formaldehyde in ref
luxing xylene does not afford the dimeric product, tetrahydroxy[2.1.2.
1]metacyclophane 6a, but furnishes the larger macrocycles 6b and 6c in
70-90% yield. AlCl3/MeNO2-catalyzed trans-tert-butylation of Ob and 6
c in toluene gives the desired metacyclophanes 7b and 7c in 60 and 80%
yields, respectively, along with tert-butyltoluene 8b. The conformati
ons of the systems such as trimer 6b and tetramers 6c, 7c have been ev
aluated from their dynamic H-1-NMR spectra. The tetramer 6c is fixed t
o form a ''pleated-loop'' conformation like the calix[8]arenes due to
the much more stronger intramolecular hydrogen bonding among the hydro
xyl groups than in the trimer 6b.