N-Isopropenylazoles: II. Fragmentation of N-Isopropenylazoles under Electron Impact

Fragmentation under electron impact of all N-isopropenylazoles, except for N-isopropenyl-2- phenylpyrrole, involves elimination of propyne or allene with formation of the corresponding NH azoles. N-Isopropenylpyrrole, N-isopropenyl-4,5,6,7-tetrahydroindole, and N-isopropenylindole give rise to rearrangement of the molecular ion into azepine structure, while the fragmentation of N-isopropenyl-2-phenylpyrrole is accompanied by transfromation into 5-methyl-5,6-dihydropyrrolo2,1-a]isoquinoline. Retrodiene decom- position is the main fragmentation pathway of the molecular ions derived from N-isopropenyl-4,5,6,7-tetrahydroindole and its 2-methyl-substituted analog. In the decomposition of 2,3-di- and 2,3,5-trimethyl-N-isopropenylpyrrole, the major fragment ions are formed from the M - H]⁺ ion having a pyridinium structure rather than from the molecular ion. N-Isopropenyldi- and -triazoles undergo fragmentation along competing pathways involving cleavage of the heteroring.