Photochemistry of Triptycene-1,4-quinone

Photolysis of 9,10-dihydro-9,10[1',2']benzenoanthracene-1',4'-quinone, C₂₀H₁₂O₂, in oxygenated acetone gives the novel photoproduct 9,10-dihydro-9,10-ethanoanthracene-11-one-12-spiro-2'-cyclopent-4'-ene-1',3'- dione, C₂₀H₁₂O₃. The reactant quinone molecule has ideal mm symmetry and lies on a crystallographic mirror plane in Pnma; the photoproduct molecule has ideal m symmetry, which is not utilized in packing in Pna2₁. This product is formed only in the presence of oxygen and a mechanism for its formation is proposed. Unreactivity in attempted solid-state photolysis can be rationalized in terms of crystal packing.

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