Hydrogen transfer in the retro‐Diels–Alder fragmentation of trans‐4‐amino‐, isopropyl‐amino‐, piperidino‐ and pyrrolidino‐2H‐1‐benzopyran‐3‐ols

The electron impact mass spectra of trans-4-amino-, isopropylamino-, pyrrolidino- and piperidino-2H-1-benzopyran-3-ols show intense peaks corresponding to the retro-Diels–Alder reaction. In addition significant ions due to hydrogen transfer to and from the retro-Diels–Alder fragment ion are observed. The transfer of hydrogen to this retro-Diels–Alder fragment ion is influenced by the nature and location of the aromatic substituents, and the amino group at C(4). The loss of hydrogen from the retro-Diels–Alder ion is subject only to the nature of the amino group at C(4). Hydrogen transfer to the retro-Diels–Alder ion is shown to arise from the gem-dimethyl group at C(2), as it is attenuated by successive removal of the methyl groups.