Under electron impact the fragmentation of 7-chloro-4,5-dioxo-2-cyclohexyl-4H, 5H-pyrano[3,4-e] [1,3] oxazine (I), 7-chloro-4,5-dioxo-2-(1'-Phenyl cyclopentyl)-4H, 5H-pyrano [3,4-e] [1,3] oxazine (11) and 7-chloro-4,5-dioxo-2t,butyl-4H, 5H-pyrano[3,4-e] [1,3] oxazine (111) has been studied. The most prominent fission in these three compounds involves the breaking of bond (alpha) to the oxazine ring giving abundant ions of substituentat C2 and a bicyclic pyrano oxazine m/e 198. In compounds II and III the ions from substituent at C2 make the base peaks of the spectra. The ion of mass 198 loses CO2 in all these compounds. Fragmentation similar to retro Diels-Alder reaction has also been observed of variable importance in these compounds. The higher mass regions in the spectra of compounds II and III have smaller peaks due to facile fragmentation of side chains. Chlorine is retained till last stages of fragmentation.
F H SAEED ,N A ZAIDI ,J M AL-KATTI ,
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