PREPARATION AND CONFORMATIONAL STUDIES OF ETHYLENE-BRIDGED CALIXARENE-ANALOGOUS MACROCYCLIC METACYCLOPHANES

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.