Equilibrating C-S bond formation by C-H and S-S bond metathesis. Rhodium-catalyzed alkylthiolation reaction of 1-alkynes with disulfides

In the presence of a catalytic amount of RhH(PPh₃)₄ (2 mol %) and 1,1′-bis(diphenylphosphino)ferrocene (dppf) (3 mol %), silylacetylenes reacted with dialkyl disulfides giving 1-alkylthio-2-trialkylsilylethynes in high yields. Alkanethiols liberated in this reaction did not interfere with the reaction, and the addition to silylacetylene forming 1-alkylthio-1-alkenes could be minimized under the conditions. Alkylacetylenes and arylacetylenes also reacted with disulfides when the alkyl or aryl groups were bulky. Diaryl disulfides gave arylthio derivatives under slightly modified conditions. The C-S bond-forming reaction is reversible: A reaction of a thiol and a 1-alkylthio-1-alkyne in the presence of the rhodium catalyst gave a 1-alkyne; alkylthio exchange reaction proceeded between a 1-alkylthio-1-alkyne and a disulfide. This is an equilibrating oxidative reaction of organic molecules with C-H and S-S bond metathesis forming C-S and S-H bonds.