The four possible 3′-uracil-1-yl and 3′-thymin-1-yl derivatives of 3′-deoxythymidine and the four analogous derivatives of 2′-deoxyuridine have been synthesised from thymidine and uridine, respectively. Advantages of the 2-(methoxycarbonyl) vinyl group to prevent the formation of anhydronucleosides and of SnCl2/PhSH/Et3N in relation to H2/Pd for the reduction of most azido groups are disclosed.