Chemoselective oxidation of phenoxathiin-based thiacalixarene and the stereoselective alkylation of products†
Phenoxathiin-based thiacalixarene, accessible via acid-catalysed rearrangement of the starting spirodienone derivative, was subjected to the oxidation of sulfur bridging groups. Using an excess of the oxidation agent, systems bearing four sulfonyl groups or three sulfonyl and one sulfoxide group are available in high yields, depending on the reaction conditions. Although four different conformations can be obtained, the alkylation with various alkylating agents led stereoselectively to derivatives being immobilized in the partial cone conformation. The structure of products was assigned using a combination of NMR techniques and single crystal X-ray analysis. All compounds represent inherently chiral building blocks potentially useful in the design of novel thiacalixarene-based receptors.