Acid catalyzed rearrangement of β-ionone epoxide

Rearrangement of β-ionone epoxide with aqueous formic acid gave 1,2-dihydro-1,1,6-trimethylnaphthalen (2), 1-(1,2,2-trimethylcyclopent-1-yl)-2-penten-1,4-dione (3), 4-(5,5-dimethyl-2-acetyl-1-cyclopenten-1-yl)-2-butanone (5), 4-(1,3,3-trimethyl-2-cyclohexanon-1-yl)-3-buten-2-one (6), 4-(2,3,6-trimethylphenyl)-2-butanone (7) and 6,6-dimethyl-2,5-10-undecatrione (8). NMR assignments are made for each compound while a computer assisted analysis of the A₂B₂ portion of 7 has been completed. Possible mechanistic pathways leading to these compounds are discussed.