Remarkably Stable S-Oxides of Calix[4]thiophenes and Their Sulfonium Ylide from Reaction of S-Oxide with Acetylene Derivative

The oxidation of macrocyclic thiophenes, such as the calix[4]thiophenes, with m-chloroperbenzoic acid in the presence of BF3·OEt2 afforded the remarkably stable mono- and bis-S-oxides based on their X-ray crystal structures. The stable mono-S-oxide of the calix[4]thiophene reacted with dimethyl acetylenedicarboxylate at 160 °C to form the thiophene-S,C-sulfonium ylide, indicating that the cycloaddition reaction did not occur.