Reactivity of phenoxathiin-based thiacalixarenes towards C-nucleophiles.

A starting thiacalix[4]arene can be easily transformed into oxidized phenoxathiin-based macrocycles 9 and 9', representing an unusual structural motif in calixarene chemistry. The presence of electron-withdrawing groups (SO2, SO) and the considerable internal strain caused by the condensed heterocyclic moiety render these molecules susceptible to nucleophilic attack. The reaction with various organolithium reagents provides a number of different products resulting from the cleavage of either the calixarene skeleton or the phenoxathiin group or both ways simultaneously. This enables the preparation of thiacalixarene analogues with unusual structural features, including systems containing a biphenyl fragment as a part of the macrocyclic skeleton. The above-described transformations, unparalleled in classical calixarene chemistry, clearly demonstrate the synthetic potential of this thiacalixarene subgroup.

The Unexpected Chemistry of Thiacalix[4]arene Monosulfoxide.

Thiacalix[4]arene monosulfoxide 4 possesses a very unusual chemistry, as demonstrated by several unprecedented derivatives in calixarene chemistry. Interestingly, compound 4 cannot be prepared by the dealkylation of its corresponding tetramethoxy derivative using BBr3. Instead, the borate complex is formed with a boron bound by the two neighboring phenolic oxygens and a sulfoxide group. A similar type of borate complex with a spirodienone fragment was then isolated as a by-product. The oxidation of monosulfoxide with Chloramine-T did not provide the expected spirodienone moiety, but rather a complex oxathiane-based spiroheterocyclic part containing a chlorine atom. X-ray analyses confirmed the structures of the unusual products and feasible formation mechanisms were proposed. These results provide further evidence of the distinction between thiacalixarene chemistry and the chemistry of classical CH2 analogues.