Electron impact and chemical ionization mass spectra of norbornane/ene di‐<i>exo</i> and di‐<i>endo</i>‐fused 1,3‐oxazin‐2(1<i>H</i>)‐ones and 1,3‐oxazine‐2(1<i>H</i>)‐thiones

Abstract

Abstract Mass spectral fragmentations of four norbornane/ene di‐ exo ‐ and di‐ endo ‐fused 1,3‐oxazin‐2(1 H )‐ones and four 1,3‐oxazine‐2(1 H )‐thiones were examined by means of metastable ion analysis, the collision‐induced dissociation technique and exact mass measurement. Under electron impact (EI) conditions all the saturated compounds gave rise to complicated fragmentations, including several rearrangements. For the unsaturated compounds, a retro‐Diels‐Alder (RDA) process was the most favoured fragmentation pathway, which took place with hydrogen rearrangement to yield RDA + H fragments. The EI mass spectra did not permit isomeric differentiation. Under chemical ionization conditions, stereochemical effects were more perceptible, but isomeric differentiation was still difficult.