The amino functions of the common 2′-deoxyribo- and ribonucleosides were blocked by the (2-cyanoethoxy)carbonyl group on treatment with 2-cyanoethyl carbonochloridate (5) or 1-[(2-cyanoethoxy)carbonyl]-3-methyl-1H-imidazolium chloride (6) leading to 7, 18, 8, 19, 9, and 20. In 2′-deoxyguanosine, the amide group was additionally blocked at the O6 position by the 2-cyanoethyl (27) and 2-(4-nitrophenyl)ethyl