A process for preparing 2',3'-didehydro-2',3'-dideoxynucleosides and 2',3'-dideoxynucleosides is described, which comprises the reductive elimination reaction of a compound of formula (I) in which X, Y, P' and B have the meanings given in the description, by reaction with zinc metal and a suitable activating agent, characterized in that the divalent zinc is removed by precipitation, from an organic phase, of the corresponding zinc sulfide, by adding a solution of a mineral sulfide to the said organic phase.