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

Abstract

Mass spectral fragmentations of four norbornaneleoe di-em-and di-endo-fused 1,3-oxazin-2( lH)-ones and four 1,3-oxazine-2(1H)-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. ~~ ~~ RESULTS AND DISCUSSION EI spectraThe 70 eV EI mass spectra of the compounds studied are presented in Table 1. Comparison of the spectra of saturated and unsaturated compounds revealed striking differences. Compounds 1 and 2 gave rise to the hardly visible molecular ion peaks. With these compounds the presence of the double bond in the carbobicyclic moiety makes a retro-Diels-Alder (RDA) reaction possible. Since this is known to be a very favoured process for

Electron Ionization Mass Spectra of Some Diexo Norbornane- and Norbornene-fused Phenyl-substituted 1,3-Oxazines and Related Systems. Competitive retro-Diels-Alder Fragmentations in 4-Phenyl-4a,5,8,8a-tetrahydro-5,8-methano-4H-benzo[e]1,3-oxazines

“…Surprisingly, the corresponding heterocyclic fragment ions were almost totally absent from the spectra of norbornene-fused 1,3-oxazine-2(1H)-ones and showed only a moderate abundance in the spectra of the thione analogs. 2 The same type of RDA fragmentation was operational in norbornene-fused 1,3-oxazines 2 and 6 ( Fig. 1(b) and Fig.…”

“…2 This process occurred with hydrogen transfer from the dienophilic (heterocyclic) part of the molecule to yield abundant cyclopentadiene cation radicals C 5 H 6 + .…”

Electron ionisation induced fragmentation of fused norbornene analogues containing SiMe2 or GeMe2 and oxygen bridges. Migration of SiMe2 and GeMe2 groups

“…The electron ionisation (EI) induced fragmentation of polycyclic rings fused together, and/or to aromatic or heterocyclic rings, is often accompanied by complex fission processes, which are in most cases the result of retro‐Diels‐Alder (RDA) reactions 1–3. An interesting case is provided by the mass spectrum of 1 which showed formation of an ion of m/z 222 4.…”