A process is provided for the preparation of branched-chain ribonucleosides of formula (I): ##STR00001## from the 1,2-anhydroderivatives of formula (II). ##STR00002## wherein PG is a hydroxyl protecting group, B is a purine or pyrimidine nucleobase, and R.sup.1 is C.sub.1-6 alkyl. The compounds of formula (I) are inhibitors of HCV polymerase useful in the treatment of HCV infection.