Synthesis, spectroscopy and computational studies of some novel phosphorylated derivatives of quinoline-5,8-diones

The neutral phosphorus nucleophiles such as R2P(Y)M [1a–f, YO or lone pair; R = Ph, tBu, OCH2C(CH3)2CH2O, PriO, EtO or MeO; M = H or SiMe3] allowed the radical addition to 2-methyl-5,8-dioxo-5,8-dihydroquinoline-7-amine (2a) and N-(2-methyl-5,8-dioxo-5,8-dihydroquinolin-7-yl)acetamide (2b) giving exclusively O-phosphorylated products, i.e.: 7-acetylamino-5-hydroxy-2-methylquinolin-8-yl diphenylphosphinate (3a), 7-acetylamino-5-hydroxy-2-methylquinolin-8-yl-tbutylphenylphosphinate (3b), 7-acetylamino-5-hydroxy-2-methylquinolin-8-yl diisopropyl phosphate (3c), 7-acetylamino-5-hydroxy-2-methylquinolin-8-yl diethyl phosphate (3d), N-{8-[(5,5-dimethyl-2-oxido-1,3,2-dioxaphosphinan-2-yl)oxy]-5-hydroxy-2-methylquinolin-7-yl}acetamide (3e), 7-amino-5-hydroxy-2-methylquinolin-8-yl dimethyl phosphate (3f) and 7-amino-5-hydroxy-2-methylquinolin-8-yl-tbutylphenylphosphinate (3g), respectively, with high yield. All products were quantitatively prepared and characterized by microanalysis, and multinuclear NMR spectroscopy. Seven of them, i.e.: 2a, 2b, 3a, 3b, 3d, 3e and 3g have been characterized by single crystal X-ray diffraction method. The geometries of the studied compounds were optimized in singlet states using the density functional theory (DFT) method with B3LYP functional. The redox properties of 2a and 2b have been studied using cyclic voltammetry. The reduction corresponds to the electrochemical behaviour of naturally occurring quinones.