Substituent-directed aralkylation and alkylation reactions of the tricyclic analogues of acyclovir and guanosine

Aryl or tert-butyl substituent in the 6 position of 3,9-dihydro-3-[(2- hydr oxyethoxy)methyl]-9-oxo-6-R-5H-imidazo[1,2-a]purine (6-R-TACV)(1) 1 partly directs aralkylation reactions into unusual positions: N-4 to give 3 and C- 7 to give N-5,7-disubstituted or N-4,7-disubstituted derivatives. In the ca se of alkylation the effect is limited to aryl substituent and position N-4 . Replacement of acyclic moiety of 1 with a ribosyl one like in 7 prevents N-4 substitution. Cleavage of the third ring of 3b to give 3-benzylacyclovi r 10 is an example of a new short route to 3-aralkyl-9-substituted guanines .