Pyrone dyes

Structurally related to the triarylmethanes is the xanthene chromogen (1.30), in which two of the aryl nuclei are linked by an oxygen atom to form a pyrone ring. Similar terminal groupings (amino, hydroxy, or both) are usually present. Xanthene dyes have mainly... 

Dye-sensitized photooxygenation of a-pyrones and a-pyrans offers the simplest access to 1,2,4-trioxanes. Examples are the conversions of (36) to (37), and (40) to (41). The photooxygenation of a-pyran (164) in methylene chloride at 0°C using tetraphenylporphin as sensitizer and a 400 W sodium lamp gives (165) (Equation (20)) <78AG(E)2ii>. 

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