Aromaticity in heterocyclic systems V. Bromination studies of certain purines,pyrrolo[3,2-d]pyrimidines and pyrazolo[4,3-d]pyrimidines

The bromination of certain selected purines, pyrrolo3,2-d]pyrimidines and pyrazolo4,3-d]-pyrimidines has been studied and the reactivity of these systems compared. Displacement of a carboxyl group by bromine was noted in the case of 6-carboxypyrrolo3,2-d]-2,4-pyrimidinedione. In contrast to xanthine, 2,6-diethoxypurine readily brominated at position 8. Pyrazolo-4,3-d]-7-pyrimidone was readily brominated at position 3.