Acid-Catalyzed Rearrangements of the Epoxides of Hexamethylbicyclohepta-2,5-dienone

Article abstract of DOI:10.1021/jo01299a013

Epoxy enone 1 rearranges in trifluoroacetic acid (TFA) at 0 deg C to hexamethyl-8-oxabicyclo<3.2.1>octa-3,6-dien-2-one (3).A mechanism involving initial protonation of the carbonyl oxygen of 1, cleavage of the C-C bond of the epoxide ring, and the intermediacy of a dicyclopropylcarbinyl-type carbocation intermediate is suggested and supported by deuterium labeling.Epoxy enone 2 rearranges in TFA at 0 deg C to give products containing the TFA moiety in a form not easily hydrolyzed by base.The products have a structure with a plane of symmetry and are thought to be stereoisomers containing a 7-norbornenone skeleton and an ortho ester type of moiety (5).A mechanism involving intramolecular trapping of a carbocation by neighboring trifluoroacetate is suggested to explain the results.Pyrolysis of 3 (500 deg C) gives pentamethylphenol.