Preparation and Conformational Studies of Ethylene‐Bridged Calixarene‐Analogous Macrocyclic Metacyclophanes

The novel macrocyclic compounds hexahydroxy[2.1.2.1.2.1]‐ ( 7b ) and octahydroxy[2.1.2.1.2.1.2.1]metacyclophane ( 7c ) have been prepared from anisole in six steps by using the tert ‐butyl function as a positional protective group on the aromatic ring. Base‐catalyzed condensation of 1,2‐bis(5‐ tert ‐butyl‐2‐hydroxy‐phenyl)ethane ( 5 ) with formaldehyde in refluxing 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. AlCl 3 /MeNO 2 ‐catalyzed trans‐ tert ‐butylation of 6b and 6c in toluene gives the desired metacyclophanes 7b and 7c in 60 and 80% yields, respectively, along with tert ‐butyltoluene 8b . The conformations of the systems such as trimer 6b and tetramers 6c, 7c have been evaluated from their dynamic 1 H‐NMR spectra. The tetramer 6c is fixed to form a “pleated‐loop” conformation like the calix[8]arenes due to the much more stronger intramolecular hydrogen bonding among the hydroxyl groups than in the trimer 6b .