Synthesis, Properties, and Redox Ability of Optically Active 3-Carba- moyl-1,6-dimethylpyrimido[4,5-c]-pyridazine-5,7(1H,6H)-dione and Related Pyrimido-annulated Pyridine Analogues

Abstract

Optically active 3-carbamoyl-1,6-dimethylpyrimido[4,5-c]pyridazine-5,7(1H,6H)-dione (13a) and related pyrimido-annulated pyridine analogues (13b,c) were prepared via the corresponding 3-ethoxycarbonyl-1,6-dimethylpyrimido[4,5-c]pydazine-5,7(1H,6H)-dione (11a) and the related compounds (11b,c). The properties of lla-c, 13a-c, and the related 1,3,6-trimethylpyrimido[4,5-c]pyridazine-5,7(1H,6H)-dione (18a) as well as 7-phenyl-and 3,7,8-trimethyl-pyrido[2,3-d]pyrimidine-2,4(3H,8H)-dione (18b,c) having no carbamoyl or ester function were studied by the UV-VIS spectra and redox potentials. Although pyridazine derivative (13a) was not reduced, pyridine derivatives (11b,c), (13b), and (18b) were reduced by Na 2 S 2 O 4 to give dihydrogenated compounds (20b,c), (21b), and (22b), respectively. The photo-induced oxidation reactions of 13a,b and 18a-c toward some amines under aerobic conditions were studied to give the corresponding imines in more than 100% yields [based on compounds 13a,b and 18a-c], suggesting that the oxidation proceeds in an autorecycling process.