Mass Spectra of New Heterocycles: XXVII. Electron Ionization Study of Polysubstituted 4,4′-Dipyrromethanes

The behavior of a series of polysubstituted 4,4′-dipyrromethanes, namely 1,1′-bis{2-amino-1-[2-(vinyloxy)ethyl]-5-sulfanyl-1H-pyrrol-4-yl}ethanes, under electron impact (70 eV) has been studied for the first time. The title compounds were synthesized in one preparative step from propargylamines, 2-(vinyloxy)ethyl isothiocyanate, and alkylating agents. Except for 5,5′-bis[(allyl-, propargyl-, and cyanomethyl)sulfanyl]­dipyrromethanes, the examined compounds give rise to stable molecular ions which decompose along three main pathways with the formation of four key cations. Two fragmentation pathways involve cleavage of the C–S bonds in the sulfanyl substituent and with the pyrrole ring to produce [M – R²]⁺ and [M – SR²]⁺ ions, respectively. The third pathway is associated with cleavage of the C–C bond between the pyrrole ring and methylene bridge connecting the pyrrole ring. In this case, two ions can be formed with the abundance ranging from 3 to 100%, depending on the substituent structure. The most abundant (up to 100% relative intensity) are radical cations [M – R² – SR²]^+·. The resulting fragment ions are stabilized via cyclization involving the vinyloxyethyl group.