Reaction of 3,7-dimethyl-6-methylthio-2-oxopurine (1) with Grignard re
agents or organolithiums afforded 8-adducts 2, whereas the correspondi
ng reaction of 3,7-dimethyl-2-oxopurine (6) gave 6-adducts 7. The addu
cts 2 and 7 were converted into 8-substituted theobromines 4 and 6-sub
stituted 3,7-dimethyl-2-oxopurines 8, respectively. 8-Chlorotheobromin
e (5) reacted with Grignard reagents in the presence of a catalytic am
ount of NiBr2(PPh(3))(2) to give 4 in good yields.