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Polysubstituted cyclopentadienes undergo oxidation and oxygen-insertion by using molecular oxygen in the presence of protic acid. The unprecedented reaction pathway provides a facile and direct approach for the synthesis of polysubstituted pyrylium salts like alpha-unsubstituted pyrylium salts, which cannot be readily prepared by traditional methods.

A facile and novel synthesis of phenylated pyrylium cations from unstrained cyclopentadiene-ring by the C-C bond oxidation in solution is presented. Phenyl-substituted cyclopentadienes are proved to form phenylated pyrylium cations in the presence of silver(I) perchlorate by insertion of an oxygen atom into the cyclopentadiene-ring.