FRAGMENTATION AND INTRAMOLECULAR CYCLIZATION IN CYCLOPENTANE-4,5-FUSED 2-N-PHENYLIMINOPERHYDRO-1,3-OXAZINES AND RELATED THIAZINES UNDER ELECTRON-IMPACT IONIZATION

The influence of cyclopentane fusion on the fragmentation behaviour of 1,3-oxazines and related thiazines was studied. The differences obser ved in the rearrangement reactions between the hydrogen atom at the or tho position of the aromatic ring and one of the hetero atoms in the c yclohexane ring were also investigated. These rearrangements occur if the cyclohexane ring contains an electrophilic atom and the carbon ato m next to it is substituted by a benzyl or arylamino group. The compou nds examined were cis and trans isomers of the title compounds substit uted with methyl and benzyl (in the latter case only the cis isomers) on the ring nitrogen. All the compounds exhibited a large [M - H]+ ion peak which decreased with increasing size of the substituent. This in dicates an intramolecular cyclization prior to further fragmentation o f the molecule. Methyl substitution seems to change the character of t his intramolecular cyclization. The main routes of fragmentation resem ble those of the cyclohexane-fused analogues more than those of the co rresponding 5,6-fused compounds. The stereoisomers fragment so similar ly that they cannot be distinguished from each other, except in the ca se of methyl substituted oxazines.