Regioselective intramolecular bridging of p-tert-butylcalix[7]arene

The first examples of singly bridged calix[7]arenes 2–4 have been obtained by base-promoted direct O-alkylation of p-tert-butylcalix[7]arene with a variety of bis-electrophiles including BrCH2Cl, oligoethylene glycol ditosylates, and 1,4-bis(bromomethyl)benzene. 1,2-Bridging was favored with ‘short bite’ spanning elements, while the 1,4-isomer predominated with the others (yields up to 72% in the presence of Cs2CO3). Assignment of bridging pattern was mainly based on chemical shift of OH groups, in some cases confirmed by 2D NMR experiments. A hampered conformational mobility, depending on the position and nature of the bridge, was observed for compounds 2–4.