Mass Spectra of New Heterocycles: XVIII. Electron Impact and Chemical Ionization Mass Spectra of Alkyl 5-Amino-3-methyl-4-(1H-pyrrol-1-yl)thiophene-2-carboxylates

Abstract

Electron impact (70 eV) and chemical ionization (methane as reactant gas) mass spectra of alkyl 5-amino-3-methyl-4-(1H-pyrrol-1-yl)thiophene-2-carboxylates have been studied for the first time. All compounds, except for tert-butyl thiophene-2-carboxylate, under electron impact give rise to stable molecular ions which decompose along two paths, depending on the site of positive charge localization (at the ester fragment or amino nitrogen atom). The main fragmentation pathway of the molecular ions is elimination of alkoxy radical from the ester group. Chemical ionization of alkyl 5-amino-3-methyl-4-(1H-pyrrol-1-yl)-thiophene-2-carboxylates involves protonation and electrophilic addition with the base peak corresponding to the [M + H]⁺ ion.