Synthesis of pyrimido [4,5-c] pyridazine (4-deazafervenulin), pyrazolo[3,4-d] pyrimidine and 6-(pyrazino-1-yl)pyrimidine derivatives

The synthesis of several pyrimido4,5-c]pyridazine (4-deazafervenulin) ( 1 ), pyrazolo3,4-d]-pyrimidine ( 2 ) and 6-(pyrazino-1-yl)pyrimidine ( 9 ) analogs has been accomplished from 6-hydrazinouracil ( 3 ). This compound could not be used as starting material for the preparation of indolo3,2-c]pyridazino3,4-d]pyrimidine derivatives ( 8 ) because it yielded the corresponding hydrazones ( 7 ).