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.