Synthesis and complexing properties of 1,5:3,7-doubly bridged calix[8]arenes with mixed spanning elements

Two different bridges were introduced at the 1,5:3,7-positions of p-tert-butylcalix[8]arene 1 using a two-step alkylation procedure. A probable cation template effect in the introduction of the second bridge was evidenced. The obtained bis-bridged derivatives 3 possess encapsulating properties toward alkali cations modulated by the length and nature of the bridges.