Mass spectra of new heterocycles: VII. Main fragmentation channels of 2-(methylsulfanyl)-4,5-dihydro-3H-azepines under electronic ionization

Abstract

Mass spectra of 3,7-di- and 3,6,7-trisubstituted 2-(methylsulfanyl)-4,5-dihydro-3H-azepines were investigated for the first time. The fragmentation of molecular ions of 3-alkoxy-substituted dihydroazepines follows the rules characteristic of ethers. The fragmentation of [M]+ of 3-phenyldihydroazepine occurred through a sequence of rearrangements; one of them led to the formation of a stable ion [M - MeS]+. A specific feature of the fragmentation of 3-(pyrrol-1-yl)dihydroazepine under the electronic ionization consists in the formation of ion [M - Me]+ with the charge mainly localized on the pyrrole ring. A partial decomposition at heating of 3-alkoxy-4,5-dihydro-3H-azepines (with alkanol elimination) resulted in 7-(methylsulfanyl)-3H-azepines. The latter under the electronic ionization give a stable molecular ion whose primary fragmentation involves the elimination of MeS group or its fragments.