One-pot Synthesis of Mono-substituted Quaternized p-tert-Butylthiacalix[4]arenes

The possibility of one-pot synthesis of mono-substituted quaternized derivatives of p-tert-butylthiacalix[4]arene was demonstrated for the first time by the reaction of distally di-bromopropyl substituted p-tert-butyl thiacalix[4]arene with several nitrogen-containing nucleophiles. The structure and composition of the reaction products were analyzed by modern physical methods, including two-dimensional NMR spectroscopy and high-resolution mass spectrometry. A detailed analysis of the reaction mixtures made it possible to reveal the dealkylation mechanism, which consists in the nucleophilic attack of the bromide ion on the O-CH2 carbon atom, followed by the formation of a brominecontaining adduct, detected by mass spectrometry. Dealkylation does not occur when the classical di-bromopropyl substituted p-tert-butyl calix[4]arene is used as a substrate - the bis-quaternized imidazolium calix[4]arene salt is formed in a high yield. Such a difference in the reactivity of two macrocycles is associated with the difference in the sizes of the macrocycles: in the case of di-substituted thiacalixarene, which has a large size, two unsubstituted hydroxyl groups form a hydrogen bond with only one alkoxy group, while in the classical calix[4]arene, two paired hydrogen bonds are formed. As a result, one of the two alkoxy groups of the thiacalixarene is more accessible for nucleophilic attack; formed thereafter thiacalixarene nucleofuge-anion is stabilized by two hydrogen bonds at once.