Reactivity of nucleophilic uracil derivatives

The reactivity of uracil derivatives bearing acidic methylene groups at N1 was investigated. On treatment with strong base, compounds with nitrile as the activating group underwent extensive dimerisation to give new tricyclic systems. Ester-activated compounds also produced dimers in the absence of an external electrophile, but their monomeric carbanions could be trapped by prompt addition of benzyl bromide to give normally alkylated products.