DFT investigation of the regioselective allylation of pyrimidine 2'-deoxynucleosides.

To understand the regioselectivity observed in the allylation of pyrimidine nucleosides and to identify the factors directing the reaction, a theoretical study of the regioselective allylation was carried out. Several key points were considered such as: the structure of the deprotonated nucleobase in the presence of Na+; the effect of the solvent on the dissociation and aggregation reactions of thymidine/Na+ ion pair; and the likely allylation reaction mechanisms involved. The results showed that the regioselectivity observed experimentally can be attributed to a greater stability of a dimeric form coupled to an increase of the reaction barrier in THF due to larger Na+ binding to the nucleobase.