Calix[4]arenes as building blocks for molecular receptors

Molecular receptors for organic molecules are described in which calix[4]arene is used as a molecular platform rather than for its cavity. This is illustrated by the synthesis of a receptor for barbiturates, a calix[4]arene in a cone conformation containing two diaminotriazine moieties at the upper rim. This receptor (9) forms a molecular cleft in which phenobarbital complexes by hydrogen bonding both triazine rings. The association constant K is 520 M 1, when the self‐association of the barbiturate is taken into account.