Preparation of bis‐pyrylium salts

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Abstract
Six methods are described for the preparation of bis‐pyrylium salts: (1) treatment of 4,4′‐bi‐2‐flavene or 4‐(4H‐flav‐2‐en‐4‐yl)flavylium perchlorate with triphenylmethyl perehlorate; (2) reaction of an aromatic o‐hydroxyaldehyde and 1,4‐deacetylbenzene under acidic conditions; (3) reaction of o‐hydroxyacetophenone, 1,4‐diacetylbenzene, perchloric acid and acetic acid; (4) reaction of a 2‐ or 4‐methylpyrylium salt with 2‐ or 4‐pyrone in the presence of phosphorus oxychloride; (5) oxidation of a 1,2‐ethanediylidenebis‐flavene or ‐thiaflavene, a bis‐flavenylidene or ‐thiaflavenylidene, and a bis‐pyranylidene or ‐thiapyranylidene by means of cupric perchlorate; and (6) reaction of 4‐methylflavylium and ‐thiaflavylium perchlorate with bromine in acetic acid.

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