4-Hydroxyquinolones-2. 247*. 4-hydroxy-2-oxo- 1,2-dihydroquinoline or 4-hydroxy-2,2-dioxo- 1н-2λ6,1-benzothiazine

Abstract

During the base-catalyzed heterocyclization of alkyl 2-[2-(alkoxycarbonyl)phenylsulfamoyl]acetates into the esters of 1-R-4-hydroxy-2,2-dioxo-1Н-2λ6,1-benzothiazine-3-carboxylic acids [2] it was observed that formation of 2,1-benzothiazine ring was somewhat more difficult than formation of quinolines from alkyl 2-[2-(alkoxycarbonyl)phenylcarbamoyl]acetates. In the current investigation, we attempted to confirm this observation with objective experimental data. For this purpose, we performed a simple and elegant experiment, allowing to estimate quantitatively the differences of how easily the structurally related 4-hydroxy-2-oxo-1,2-dihydroquinoline and 4-hydroxy-2,2-di-oxo1Н-2λ6,1-benzothiazine heterocycles were formed. The starting material for this study was the dianilide of sulfoacetic acid 2 obtained by the reaction of methyl N-methylanthranylate (1) with (chlorosulfonyl)acetyl chloride. The acylation in these experiments was performed under conditions designed to exclude even partial intramolecular cyclization by avoiding sufficiently strong bases (such as tertiary alkylamines) commonly used in reactions of this type for neutralization of HCl evolved. Dianilide 2 can theoretically convert by the action of basic catalysts into either benzothiazine 3 or quinoline 4, or a mixture of these compounds, and the unique structure of compound 2 creates identical conditions for formation of both heterocycles, that would be difficult to achieve otherwise. Further, the experiment involves essentially a qualitative and quantitative analysis of the reaction mixtures formed by treatment of dianilide 2 with bases. This study relies of unequivocal structural