A novel ring-enlargement oxidation of polyphenyl substituted cyclopentadienes in air (or molecular oxygen) promoted by perchloric acid was described, in which an oxygen atom was inserted into the cyclopentadiene-ring, forming a six-membered pyrylium salts. The structure of the resulting pyrylium salts was confirmed by FT/IR, ¹H NMR, ¹³C NMR, MS spectroscopies and elemental analyses.

Key words: polyphenyl substituted cyclopentadiene, cleavage of carbon-carbon bond, ring-enlargement reaction, pyrylium salt