DFT study of the rearrangement of 5-oxymethyl-1,3-oxathiolane-2-imine to thiiran-2-ylmethyl carbamate

Rearrangement of 5-oxymethyl-1,3-oxathiolane-2-imine under alkali conditions was studied by B3LYP/6-311+G(d) method. Calculations showed that only the pathway leading to formation of thiirane is possible. Oxymethyl-1,3-oxathiolane-2-imine intermediate can be formed by deacylation of the corresponding acyloxymethyl derivative or after cyclization of unstable 2-oxyranylmethyl N,N-dimethylthiocarbamate. The deacylation pathway includes anionic species whereas the rearrangement via thiocarbamate goes through zwitterionic and neutral species. For the first way, the rearrangement of oxymethyl-1,3-oxathiolane-2-imine to (2-imino-1,3-dioxolan-4-yl)methanethiol through bicyclic transition state has the highest energy barrier. For the second way, the rearrangement of 2-oxyranylmethyl thicarbamate to oxymethyl-1,3-oxathiolane-2-imine has the highest energy barrier. The anionic and neutral bicyclic structures are differing in CO and CS bond lengths and in ellipticity of the carbon–nitrogen double bond.