A novel type of nucleotide analogues, the 2′,3′-O-(1-diethylphosphono)alkylidene derivatives of ribonucleosides was prepared by redox reaction of diethyl chlorophosphite with various nucleoside orthoesters. Some of these compounds undergo interesting rearrangements when treated with nucleophiles. The configuration of the title compounds was determined by 2D-ROESY experiments. Biological activity of