The phosphorylating reagents CF3P (NMe2) Cl and CF3P (NEt2) Cl are used to phosphorylate the 3′-hydroxyl moiety of several protected 2′-deoxynucleosides yielding the corresponding nucleoside trifluoromethyl phosphonamidites. Their scope and limitations towards amidite activation are investigated but, however, their behavior is completely different to commonly used nucleoside phosphorus amidites.