Pyrylium salt

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Chemical properties

The carbon to oxygen double bond is also an oxonium ion which due to aromatic stabilization is much less reactive than ordinary oxonium ions. However, the parent compound pyrylium is unstable in neutral water like oxonium salts. Pyrylium cations react with nucleophiles in the 2,4 and 6 positions and may result in ring-opening reactions.

Pyrones

A pyrylium cation with a hydroxyl anion substituent in the 2-position is not the zwitterionic aromatic compound (1) but a neutral unsaturated lactone or an α-pyrone or pyran-2-one (2). Important representatives of this class are the coumarins. Likewise a 4-hydroxyl pyrylium compound is a φ-pyrone or pyran-4-one (4) to which group belongs a compound such like maltol.

Chemical properties

2-Pyrones are known to react with alkynes in a Diels-Alder reaction to form arene compounds with expulsion of carbon dioxide, for example:^[2]

Chromenylium ion

  The benzo-fused pyrylium ion is also called benzopyrilium or according to IUPAC chromenylium ion. This is the charged version of 1-benzopyran or chromene (IUPAC).

Flavylium ion

In biology, the ion 2-phenylchromenylium is referred to as flavylium. A class of flavylium derived compounds are anthocyanins, i.e. pigments which are responsible for the colors of many flowers.

See also

• 6-membered aromatic rings with one carbon replaced by another group: borabenzene,benzene, silabenzene, germanabenzene,stannabenzene, pyridine, phosphorine
• Pyrans are pyrones lacking the ketone group.

References

External links

• "2,6-Di-tert-butyl-4-methylpyrylium trifluoromethanesulfonate" Organic Syntheses, Coll. Vol. 7, p.144 (1990); Vol. 60, p.34 (1981).