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.