[PH2](O)=O.N([O-])=O.[Na+].N[C:9]1[C:18]2[C:19](=[O:26])[CH:20]=[C:21]([C:23]([OH:25])=[O:24])[O:22][C:17]=2[C:16]([CH2:27][CH2:28][CH3:29])=[C:15]2[C:10]=1[C:11]([Cl:33])=[CH:12][C:13]([C:30]([OH:32])=[O:31])=[N:14]2>S(=O)(=O)(O)O.O.C(O)(=O)C>[Cl:33][C:11]1[C:10]2[C:15](=[C:16]([CH2:27][CH2:28][CH3:29])[C:17]3[O:22][C:21]([C:23]([OH:25])=[O:24])=[CH:20][C:19](=[O:26])[C:18]=3[CH:9]=2)[N:14]=[C:13]([C:30]([OH:32])=[O:31])[CH:12]=1Cold hypophosphorous acid (50%, 20 ml) was added slowly to a solution of sodium nitrite (3.7 g) in sulphuric acid (100 ml) diluted with water (50 ml), maintaining the temperature from -5° to -10°. The reaction mixture was cooled to -15°, and a cooled solution containing 5-amino-6-chloro-4-oxo-10-propyl-4H-pyrano[3,2-g]quinoline-2,8-dicarboxylic acid (0.753 g) in acetic acid (200 ml), added over two hours maintaining the temperature between -10° and -15°. When the addition was complete, the slurry was stirred for an hour, and the mixture allowed to warm to 5° C. The mixture was stored in a refrigerator overnight, with the evolution of nitrogen and oxides of nitrogen. Filtration of the reaction mixture, and recrystallisation from ethyl acetate, gave 0.43 g of the title compound, mp 338°-340° C.
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