Bicyclo octene-2,8-diones

The corresponding bicyclo[2.2.2]octene derivatives provided an equilibrium mixture (8 1) with only minor amounts of the retro-Claisen product36. The Diels - Alder adduct from diphenylful-vene and (Z)-hex-3-en-2,5-dione rearranged completely to the corresponding dihydropyran at 45°C in ethanol37. 

Dipolar cycloaddition of 3//-1.2.4-triazole-3,5(4// )-diones to strained bicyclic alkenes generally leads to the formation of rearranged 1,2,4-triazolidines (Section7.2.10.1.), although bicyclo[2.2.2]-octene does not react and cyclopentadiene dimer gives exclusively the cne reaction product24. 

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