AbstractThe synthesis of the crystalline and easily accessible phosphorylating agent 4‐nitrophenyl 4‐morpholinylphosphonochloridate is reported. Its application to the preparation of 5′‐phosphorylated ribonucleosides (e.g.pA, ppA and pppA) as well as RNA fragments (e.g.pUpU and ppUpU) is demonstrated. Further, special attention is paid to the mild removal of the 4‐nitrophenyl group from fully protected phosphotriester inte