A flexible synthesis of the four stereoisomeric enantiomerically pure 5 -nor carbocyclic adenosine analogues 4b, ent-4b, 5b and ent-5b starting from the common enantio-merically pure allylic monoacetate 3 has been developed. Each of the nucleoside analogues was transformed into the corresponding 4 -phosphonates and subsequently into the diphosphoryl-phosphonates 4e, ent-4e, 5e, and ent-5e, respectively.