A new and efficient synthetic approach to dichlorofluoflavines. Study of the stability of isomeric fluoflavines by HF and B3LYP procedures

The first method for the synthesis of 7,10-dichloro-5,12-dihydroquinoxalino[2,3-b]quinoxalines is reported. Treatment of 3,3,6,6-tetrachloro-1,2-cyclohexanedione with diaminomaleonitrile leads to 5,8-dichloro-2,3-dicyanoquinoxaline in near quantitative yields. This compound has been found to be an excellent synthetic equivalent of unavailable 2,3,5,8-tetrachloroquinoxaline. It reacts with o-phenylenediamines providing the corresponding dichlorofluoflavines in fair to high yields. These compounds have been identified by NMR spectroscopy and X-ray crystallography. Molecular structures, chemical hardness, ΔG298≠-values, and relative stabilities of all possible isomeric products have been calculated by HF and B3LYP density functional theory methods.