The present invention relates to a process for preparing a compound of formula 682-4, said process comprising the steps of: (i) converting a compound of formula 682-1 into a compound of formula 682-2'; (ii) converting said compound of formula 682-2' into a compound of formula 682-3; and (iii) converting said compound of formula 682-3 into a compound of formula 682-4. Further aspects of the invention relate to the use of the above process in the preparation of 2'-cyano-2'-deoxy-N