Abstract The phosphonyl radical generated from the reaction of dimethyl phosphite with manganese(III) acetate adds selectively to the 3-position of pyridin-2-ones or the 5-position of pyrimidin-4-ones to afford phosphonylated products in good yields. The phosphonyl radical generated from the reaction of dimethyl phosphite with manganese(III) acetate adds selectively to the 3-position of pyridin-2-ones