Stereochemical studies. Part 67. Saturated heterocycles. Part 52. The mass spectra of some condensed skeleton 1,3‐oxazin‐4‐one derivatives

The mass spectrometric behaviour of twenty saturated heterocyclic compounds with a 1,3‐oxazin‐4‐one moiety fused with cis or trans anellation to a cycloalkane ring (C5‐C8) was studied. The roles of the C‐2 and N‐3 substituent(s) were found to be characteristic, while the size of the cycloalkane ring seemed to be unimportant. Some fragmentation processes involving breakdown of the oxazinone ring of the cis or trans isomers displayed significant stereoselectivity. A striking new decomposition process involving significant chlorine elimination from the molecular ion of some 2‐p‐chlorophenyl derivatives was observed and was studied in some detail.