Synthesis and antioxidant properties of some novel 1,3,4,2-oxadiazaphosphepino[6,7-<i>c</i>]quinolinones and pyrazolo[3,4:4′,3′]quinolino[5,1-<i>c</i>][1,4,2]oxazaphosphinine

<p></p> <p>A series of novel 1,3,4,2-oxadiazaphosphepino[6,7-<i>c</i>]quinolinones <b>3</b>–<b>5, 9</b>, and <b>11</b> have been synthesized from treatment of 4-hydroxy-1-methyl-3-[1-(2-phenylhydrazinylidene)ethyl]quinolin-2(1<i>H</i>)-one (<b>2</b>) with some phosphorus sulfides, diethyl phosphite and phenyl phosphonic dichloride, respectively, in dry dioxane. Also, reaction of hydrazone <b>2</b> with tris(2-chloroethyl)phosphite under the same reaction conditions gave pyrazolo[3,4:4′,3′]quinolino[5,1-<i>c</i>][1,4,2]oxazaphosphinine <b>10</b>. However, when hydrazone <b>2</b> was treated with phosphonic acid, phosphorus tribromide or phosphorus oxychloride, 3,5-dimethyl-1-phenyl-1,5-dihydro-4<i>H</i>-pyrazolo[4,3-<i>c</i>]quinolin-4-one (<b>7</b>) was isolated in all cases. The compounds were evaluated for their antioxidant activities. Among the synthesized compounds, 1,3,4,2-oxadiazaphosphepino[6,7-<i>c</i>]quinolinone-2-sulfide <b>5</b> and its analogue 2-oxide <b>11</b> exhibited higher antioxidant activities than the standard antioxidant.