Syntheses of 6- or 8-Carbon-Substituted 2-Oxopurines

Reaction of 3,7-dimethyl-6-methylthio-2-oxopurine (1) with Grignard reagents or organolithiums afforded 8-adducts (2), whereas the corresponding reaction of 3,7-dimethyl-2-oxopurine (6) gave 6-adducts (7). The adducts (2) and (7) were converted into 8-substituted theobromines (4) and 6-substituted 3,7-dimethyl-2-oxopurines (8), respectively. 8-Chlorotheobromine (5) reacted with Grignard reagents in the presence of a catalytic amount of NiBr 2 (PPh 3 ) 2 to give (4) in good yields