Pyrrolopyrimidines. 5. Reaction of 6-Amino-1,3-dimethylpyrrolo[3,4-d]pyrimidine-2,4(1H,3H)-diones with 1,3-Diketones

The reaction of 6-amino-1,3-dimethylpyrrolo3,4-d]pyrimidine-2,4-dione with 1,3-diketones leads to formation of predominantly pyrimido4',5':3,4]pyrrolo1,2-b]pyridazine-2,4(1H,3H)-diones and, to a lesser extent, pyrimido5',4':3,4]pyrrolo1,2-b]pyridazine-1,3(2H,4H)-diones. The ease and direction of the cyclization reaction suggests a very -electron rich pyrrole ring in the initial state, especially in the position 7.