Primary and secondary electrophilic radicals such as : .CHRCO2CH3(R=H,CH3,CO2CH3) and tertiary .CCl3, radical were added directly at C-8 of, the model purine compound, caffeine to give the corresponding 8-substituted derivatives in fairly good yields. Unexpected reaction of caffeine with oxy radicals from the initiators (PhCo2., t-BuOO.) gave rise to C-5 substituted 1,3,7-trimethyl-5,7-dihydrouric