Phosphorylation of the easily accessible 3',5'-diesters 1a-d with diphenyl phosphorochloridate, followed by selective 5'-deacylation, affords the phosphotriester derivatives 2a-d in good yields. Alkaline treatment of 2a-d results in the formation of the 2',3'-cyclic phosphates (3a-d). The usefulness of the phosphotriester derivatives 2a-d is also demonstrated in the synthesis of the nucleotidyl-(3'-5')nucleoside 3'-phosphates U-Up (10a), U-Ap (11a), U-Cp (12a) and A-Gp (13a). The fully protected dinucleoside diphosphates 5c-8c, prepared by the phosphotriester method, are deprotected in two ways: (a) by a purely chemical method, affording the dinucleoside diphosphates in a circa one to one mixture of 2'- and 3'- isomers, 10b-13b and 10a-13a, respectively, and (b) by a mixed chemical-enzymatical approach which gives the pure 3'-phosphates (10a-13a).