Procedures are described for the synthesis of nucleoside 5 '-diphosphates, methanediphosphonates, and di-fluoromethanediphosphonates. The general strategy involves protection of the nucleosides as amidine, 2', 3 '-methoxymethylidene, and 3'-(tert- butyldimethylsilyl) derivatives prior to tosylation with tosyl chloride and (N, N- dimethy1amino) pyridine. Deprotection, followed by displacement of the tosyl moiety with ...