Catalytic oxidative dimerization of <i>β</i> -thioxoketones and aromatic thiols using lanthanide salts

In this study, a catalytic activity of trivalent lanthanide ion was found for an oxidative dimerization of β-thioxoketones (monothio-β-diketones) and thiols under aerobic conditions to yield disulfide compounds. The dimerization reaction was accelerated under the existence of lanthanide salts, such as Ln(OTf)3 (OTf: trifluoromethanesulfonate) (Ln = Ce, Eu, Lu) and Eu(tfa)3(H2O)3 (tfa: trifluoroacetic acid). In particular, dimerization of β-thioxoketones derivatives was completed within <1 h with Eu(OTf)3 in EtOH-d6. The reaction was also applied to thiols, such as 2-naphthylthiol, 4-aminobenzenethiol, and 1-dodecanethiol. While aromatic thiols also afforded disulfide dimers, aliphatic thiols did not react. These acceleration effects could be come from the coordination capability of multiple guest substrates on the lanthanide ions in solutions. This new method of dimerization reaction is quite easy and mild for obtaining disulfide compounds.