A case of unusual sterically driven C-tritylation reaction of tricyclic analogues of acyclovir

Article abstract of DOI:10.1016/S0040-4020(98)83029-9

3,9-Dihydro-3-[(2-hydroxyethoxy)methyl]-6-methyl-9-oxo-5H-imidazo[1,2-a]purine (1) and its silylated derivative (2) when tritylated under conditions suitable for regioselective N-5 alkylation underwent instead C-substitution to give 7-trityl (12, 3) and 7-(4-benzhydrylphenyl) (13, 4) derivatives as major and minor products, respectively. Substrates lacking 6-Me group (5, 6) yielded 5-tritylated (10, 7) and 5,7-ditritylated (11, 8) major products and 7-tritylated (9) minor product. The regioselectivity of the reaction seems to be driven mainly by steric hindrance of the 6-Me substituent.