Nitrenium ion induced tandem S–S coupling, 1,2-prototropic shift and reduction

Diazotization of 4-amino-1,2,4-triazole-5-thiones in the presence of tetrafluoroboric acid generates the corresponding transient nitrenium ions that induce tandem oxidative S–S coupling, 1,2-proton shift and reduction leading to the formation of bis(1,2,4-triazol-5-yl)disulfides. The activation energy barrier for the conversion of 5-thioxo-3-phenyl-1,2,4-triazole-4-diazonium tetrafluoroborate into the corresponding nitrenium ion, namely 5-thioxo-3-phenyl-1,2,4-triazolenium tetrafluoroborate, calculated at the DFT level (B3LYP/6-31+G∗∗), is found to be 9.51 kcal mol−1 only. The X-ray crystal structure as well as theoretically optimized geometry of the resulting disulfide reveals that the two halves of the molecule are oriented orthogonally to minimize repulsion between the lone pairs of electrons on the two sulfur atoms.