The acylation of 3',5'-di-O-(chloroacetyl)-5-fluoro-2'-deoxyuridine (I) with 3,4-methylenedioxybenzoyl chloride (II) by means of triethylamine in dichloromethane gives 3',5'-di-O-(chloroacetyl)-3-(3,4-methylenedioxybenzoyl)-2'-deoxy-5-fluorouridine (III), which is then hydrolyzed with triethylamine in methanol-THF.