Abstract: A process for the production of a 5-substituted derivative of a 2,3'-anhydro-2'-deoxyuridine preferably corresponding to the following general formula: ##STR1## wherein R.sup.1 represents H, alkyl, aryl, halogeno or CF.sub.3 ; characterized in that it comprises heating a 5-substituted derivative of a 2'-deoxyuridine preferably corresponding to the following general formula: ##STR2## wherein R.sup.1 is as defined above; in the presence of a sulphite transfer reagent and preferably a solvent is disclosed.This process improves the production of valuable intermediates and hence facilitates and reduces the cost of production of pharmacologically-interesting compounds.