Pyrolysis reactions of nonafluorobiphenyl-4-yl prop-2-enyl ether: a remarkable rearrangement reaction of an intramolecular Diels–Alder product

The title compound 16 on flash vapour pyrolysis (FVP) at 350 degrees C gives a complex mixture which includes 20, the product of one of the two possible intramolecular Diels-Alder reactions of the cyclohexa-2,4-dienone intermediate 17 formed via a Claisen rearrangement reaction. FVP of 16 at 420 degrees C gives the bicyclic compound 30, formed not from the other possible Diels-Alder adduct 27 but from an isomer 31 having exactly the same carbon skeleton, but produced as a transient intermediate via a rare retro-cyclisation reaction of 20 to a tethered ketene 32 and recyclisation via the alternative mode.