The first synthesis of allenic nucleosides derived from natural ribonu
cleosides is reported. 2'-Deoxy-2'-(ethenylidene)cytidine (8) and 2'-d
eoxy-2'-(ethenylidine)adenosine (21) were prepared by a modification o
f the method developed by Tsuji and co-workers for the synthesis of al
lenes. The biological rationale for the synthesis of these compounds i
s discussed.