Structure of the diene originating from a retro‐Diels–Alder cleavage, of the natural product kuwanon g

Fragmentation of a natural Diels–Alder adduct, kuwanon G, has been examined using fast-atom bombardment and collision-induced dissociation (CID) techniques. The CID spectrum of a diene ion originating from a retro-Diels–Alder cleavage of the [M + H]+ ion gave an intense peak arising from the fragmentation of the diene moiety, as well as characteristic peaks arising from the fragmentation of a tautomeric 2,2-dimethylpyran ring structure. The results obtained suggest that the diene can be irreversibly converted into the 2,2-dimethylpyran ring structure under gas-phase mass spectrometric conditions.