“…However, another strong electron-withdrawing group, the nitroso group, has received little attention as an activator of nucleophilic substitution, even when it is one of the most widely employed to introduce a nitrogen functionalisation at C (5) in pyrimidine derivatives during the synthesis of azaheterocycles fused with pyrimidine (i.e., purines, 8-azapurines, pteridines, etc.). There are some precedents [5][6] indicating that a 5-nitroso group can act as strong activator of nucleophilic substitution of alkylthio groups from pyrimidines. However, the studies have not been, to our knowledge, extended to the activation of other leaving groups.…”