synthesizing 3',5'-dithio-2'-deoxypyrimidine nucleosides 6 and 13 from normal 2'-deoxynucleosides. 2,3'-Anhydronucleosides 2 and 9 are applied as intermediates in the process to reverse the conformation of 3'-position on sugar rings. The intramolecular rings of 2,3'-anhydrothymidine and uridine are opened by thioacetic acid directly to produce 3'-S-acetyl-3'-thio-2'-deoxynucleosides 3 or 5. To cytidine