Michaela Pojarová

Uncommon regioselectivity in thiacalix[4]arene formylation.

To reveal the alternative ways for upper-rim thiacalixarene derivatization, the formylation reactions (Gross and/or Duff conditions) of the corresponding tetrapropoxythiacalix[4]arene immobilized in the 1,3-alternate conformation were systematically studied. Surprisingly, albeit using an excess of the formylation agent, only two formyl groups were introduced exclusively into the meta positions of thiacalixarene skeleton. Unexpected regioselectivity of these reactions opens the door for a unique substitution pattern in thiacalixarene chemistry. The formation of meta-substituted aldehydes is another illustration showing remarkably different reactivity of the thiacalix[4]arene system compared with that of a classical calyx[4]arene analogue.

Unusual Intramolecular Bridging Reaction in Thiacalix[4]arene Series

Thiacalix[4]arene immobilized in the cone conformation undergoes a direct formylation reaction giving unusual products in high yields. The Duff reaction (urotropine/TFA) leads to unprecedented intramolecularly bridged compounds possessing two formyl groups on the opposite para- or para-/meta-positions. The comparison with the corresponding classical calix[4]arene analogues indicates an amazingly different reactivity of the thiacalix[4]arene system.

Systematic approach to new ligands for anion recognition based on ureido-calix[4]arenes

Mono, di-, tri- and tetraureido-calix[4]arenes in the cone, partial cone and 1,3-alternate conformations have been synthesised and their complexation ability towards selected anions has been studied. The structure–anion complexation ability relationship has been systematically monitored. A new type of very efficient ligands based on diureido-calix[4]arene in a 1,3-alternate conformation with pronounced bonding ability towards carboxylates was designed.

Simple synthesis of calix[4]arenes in a 1,2-alternate conformation

The least accessible calix[4]arene conformers-1,2-alternates-can be very easily prepared using a proximal dialkylation and subsequent peralkylation reaction sequence.