Fragmentation of Cyclic Carboxonium Ions, IV. - Synthesis of β-Oxa-γ, δ-enones
The proton-catalyzed fragmentation of 4-methylene-1,3-dioxolanes 2 by weak acids (pK > 4.3) or weak acidic ion exchangers leads in good yields to β-oxa-γ, δ-enones 5 which are thus easily and generally available for the first time.