2,6-Diamino-4-hydroxypyrimidine (I) was cyclized with 1,3-dichloroacetone (II) in DMF at room temperature, and the resulting unstable furopyrimidine (III) was rapidly purified by a short column of silica gel and stored at -20 C. Then, the nucleophilic displacement reaction of chloride (III) with 2-naphthalenethiol (IV) in the presence of potassium carbonate in DMSO yielded the desired thioether.