Aryl or tert-butyl substituent in the 6 position of 3,9-dihydro-3-[(2-hydro
xy-ethoxy)methyl]-9-oxo-6-R-5H-imid 1 directs the benzylation reaction part
ly into N-4 position to give 3. Cleavage of the third ring of 3 gives 3-ben
zylacycloguanosine 5, a first 3-aralkilo-9-substituted guanine.