Thiopyrylium salts benzene ring

Pyrylium salts, especially the 2,4,6-triaryl substituted, react with a wide variety of nucleophiles some of which lead to the formation of rings other than benzene or pyridine. Sodium sulphide, for instance, attacks the pyrylium ring at C-2 to produce the blue-coloured dienone (78) which then cyclizes on treatment with add to the thiopyrylium salt (79) (56HCA207). 

Zimmermann and Klaus (1996) have reported a method in which the ring of the pyryUum and thiopyrylium salts (135) have been transformed to substituted benzene ring (136,137) by treatment with anhydrobases derived from IH-benzimidazolium and benzothioazolium salts (Scheme-37) (Zirrimerrnann Schrnidt 1996). 

Scheme 37. Conversion of pyrylium and thiopyrylium salts to substituted benzene ring...

---