Stability of pyrimidine N-glycosydic bonds in the presence of Lawesson’s reagents: revisit of 2-thiolation of pyrimidine nucleosides

2-Thiolation of O4-phenylthymidine and 4-thiothymidine using Lawesson’s reagents proceeded differently. The glycosydic bond of O4-phenylthymidine quickly dissociated when treated with Lawesson’s reagent, whereas 4-thiothymidine was reasonably stable and can be converted to 2,4-dithiothymidine. A hypothesis that involves a cationic pyrimidine intermediate facilitating SN1 cleavage was proposed.