Mass spectrometric intramolecular cyclization reactions of some 2‐N‐phenyliminoperhydro‐1,3‐oxazines

Mass spectrometric fragmentation of four monocyclic and eight condensed skeleton 2‐N‐phenyliminoper‐hydro‐1,3‐oxazine derivatives have been characterized by metastable ion analysis, collision induced dissociation measurements, exact mass measurements and ion structural studies. Extensive rearrangement reactions, best characterized in terms of intramolecular cyclizations, took place. Namely, when R = H the N‐cyclization was almost exclusive whereas in cases where R > H steric reasons rendered the O‐cyclization more feasible. Part of the fragmentation of the R = H compounds seemed to occur via the amino form. On the other hand the methane chemical ionization spectra of cis‐ and trans‐anellated 5,6‐trimethylene‐2‐N‐phenyliminoperhydro‐1,3‐oxazines proved that at least some imino structure was present in the gas phase.