The reaction of 5-vinyl-2'-deoxyuridine (I) with benzoyl chloride in the presence of pyridine and diisopropylethylamine gives 3,3',5'-tribenzoyl-5-vinyl-2'-deoxyuridine (II). Subsequent reaction of (II) with phenyl(tribromomethyl)mercury in benzene at reflux yields a mixture of 5-[(1S)-2.2-dibromocyclopropyl]-3,3',5'-tribenzoyl-2'-deoxyuridine (III, m.p. 220 C) and 5-[(1R)-2,2-dibromocyclopropyl]-3,3',5'-tribenzoyl-2'-deoxyuridine (IV, m.p. 228 C) diastereomers which are separated by silica gel column chromatography (1:1 ratio) using a solvent gradient starting with toluene and ending with toluene: ethyl acetate (19:1 v/v). The absolute configuration of 5-[(1S)-2,2-dibromocyclopropyl]-2'-deoxyuridine (V), obtained by treatment of III with ammonia in methanol, was established by single crystal X-ray analysis. Treatment of IV with ammonia in methanol, to remove the benzoyl protecting groups, affords MW-60U.