Experimental and theoretical study of the gas-phase interaction between ionized nitrile sulfides and pyridine

The gas-phase reactivity of ionized nitrile sulfides, R-C≡N⁺-S^·, towards neutral pyridine was studied both experimentally (six sector hybrid mass spectrometer) and theoretically (density functional theory and Møller-Plesset ab initio calculations). An ionized sulfur atom transfer and a cycloaddition process respectively yielding ionized pyridine N-thioxide and a thiazolopyridinium cation were observed. Whereas the very efficient S^·+ transfer reaction probably involves the intermediacy of several ion-molecule complexes, the thiazolopyridinium ion formation is likely to be initiated by an electrophilic attack of the R-C≡N⁺-S^· ion on the nitrogen atom of pyridine; the resulting intermediate then undergo an intramolecular substitution of an α-hydrogen atom by the sulfur atom.