New fragmentation pathways in the electron impact mass spectrometry of derivatized pyrano‐1,3‐diphenylprop‐2‐enones

The fragmentation patterns of closely related chalcones, cinnamoylchromans and cinnamoylchromenes, are reported to be strikingly different. The mass spectra of the first group show peaks typical of the fragmentation of simple chalcones balanced by additional fragmentation routes competing effectively with the typical chalcone fragmentation. For the other group with the introduced double bond the fragmentation is considerably changed. Initial loss of a methyl group gives rise to formation of the base peak in three of four examples. The [M – CH3]+ ion decomposes further, eliminating a styrene yielding the m/z 187 ion. This process may be rationalized as a retro‐Diels–Alder fragmentation of a flavanone formed on intramolecular rearrangement of the molecular ion.