Disulfide bonds of 2-isocyanatophenyl methyl disulfide and 2-endo-isocyanato-6-endo-(methyldisulfanyl)bicyclo[2.2.1]heptane showed neighboring group participation in the formation of thiocarbamates. Natural Bond Orbital (NBO) analyses revealed that the unusual nucleophilicity requires a rigid through-space interaction between a lone pair of the disulfide bond and an antibonding orbital of isocyanate.