Hydrogen transfer in the retro Diels-Alder fragmentation of oxygen-containing heterocyclic Compounds. I—chromanones and 4-hydroxychromans

The mass spectra of 2,2-dimethylchromanones and 2,2-dimethyl-4-hydroxychromans show peaks corresponding to the ions formed by the retro Diels-Alder reaction with or without hydrogen transfer to the ion. The hydroxychromans also show peaks corresponding to an ion formed by the loss of hydrogen from the ion formed by the retro Diels-Alder reaction. Deuterium labelling showed that the hydrogen transferred in the chromanones arises from the gem-dimethyl groups on C-2, and the hydrogen atom lost in the case of the hydroxychromans is from C-4, the carbinyl carbon.