Mass Spectra of New Heterocycles: XXIV. Electron Impact and Chemical Ionization Study of Methyl N-[3-Alkoxy- and 3-(1H-Pyrrol-1-yl)thiophen-2-yl]carbamimidothioates

Previously unknown methyl N-(3-substituted thiophen-2-yl)carbamimidothioates were synthesized in one preparative step from hetero-substituted allenes (methoxy-, 1-ethoxyethoxy-, and 1H-pyrrol-1-ylallenes) and aliphatic, cycloaliphatic, and aromatic isothiocyanates, and their behavior under electron impact (70 eV) and chemical ionization (reactant gas methane) was studied for the first time. Unstable molecular ion derived from the title compounds under electron impact decomposes mainly via C-N bond cleavage in the carbamimido-thioate fragment with charge localization on the imide nitrogen atom. A similar fragmentation pathway is observed in the chemical ionization mass spectra of these compounds. Characteristic but low-intense ion peaks in the electron impact mass spectra of methyl N-(3-methoxythiophen-2-yl)carbamimidothioates become predominating in their chemical ionization mass spectra. The base peak in the chemical ionization mass spectra of methyl N-[3-(1H-pyrrol-1-yl)thiophen-2-yl]carbamimidothioates is that of the [M - SMe](+) ion. The most abundant ion in the chemical ionization mass spectrum of methyl N-[3-(1-ethoxyethoxy)thiophen-2-yl]-carbamimidothioate was generated by successive elimination of ethoxyethene and methanethiol molecules from the [M + H](+) ion.