Quinolone analogues 7 [1-6]. Synthesis of 3-Heteroaryl-1-methylpyridazino[3,4-b]quinoxalin-4(1H)-ones

The 3-heteroaryl-1-methylpyridazino[3,4-b]quinoxalin-4(1H)-ones 6a-e were synthesized by the oxidative-hydrolytic ring transformation of the 3-heteroaryl-1,2-diazepino[3,4-b]]quinoxaline-5-carbonitriles 9a-c, which were obtained by the 1,3-dipolar cycloaddition reaction of the 2-(2-heteroarylmethylene-1-methylhydrazino)quinoxaline 4-oxides with 2-chloroacrylonitrile. The assignment of the thiophene and furan ring protons was carried out through the data of the NOE, decoupling, and coupling constants.