Chelation-controlled regioselective alkylation of pyrimidine 2′-deoxynucleosides

Protection-deprotection steps, which are usually needed for regioselective alkylation of pyrimidine deoxynucleosides, can be avoided by choosing the appropriate solvent. The combined effects of low dielectric constant and possible sodium chelation by pyrimidine nucleosides may account for the unexpected regioselectivity observed in THF.