Reactions of 7- and 9-aminoadenines with 2,4-pentanedione. Formation of new ring systems, pyridazino[6,1-f]purine and pyridazino[1,6-e]purine

Reactions of 7-aminoadenines with 2,4-pentanedione yielded pyridazino[6,1-f]purines and 5-pyrazolylpyrimidines. The structure of the latter was identified by X-ray analysis. Reaction of 9-amino-N6-methyladenine with 2,4-pentanedione gave pyridazino[1,6-e]purine and Schiff base products. Possible reaction mechanisms are discussed.