The synthesis of pyrimido[4,5-c] pyridazines and pyrido[2,3-d]pyrimidines related to toxoflavin and fervenulin

4-Deazatoxoflavin (1,6-dimethyl-1,5,6,7-tetrahydropyrimido[4,5-c]-5,7-pyridazinedione) ( 7 ) and several other 4-deazatoxoflavin and 4-deazafervenulin analogs have been prepared with the required intermediates. 3,5,7-Trimethyl-1,2,3,4-tetrahydropyrido[2,3-d]-2,4-pyrimidinedione ( 19 ) and 8-phenyl-3,5,7-trimethyl-2,3,4,8-tetrahydropyrido[2,3-d]-2,4-pyrimidinedione ( 20 ) were also prepared.