L. Thomas, Archana Gupta, Vandana Gupta
2002
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0
Influential Citations
2
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Journal
Heterocyclic Communications
Abstract
Synthesis of 3,5-dimethyl / 3,7-dimethyl-4H-l,4-benzo-thiazines is reported by the condensation and oxidative cyclization of 2-amino-3-methyl / 5methylbenzenethiols with compounds containing active methylene group in dimethylsulfoxide. The reactions proceed through the formation of intermediate enaminoketones. The compounds containing active methylene group viz. benzoylacetones have been prepared by the Claisen condensation of acetophenones with ethylacetate. The IR, NMR and Mass spectral studies are also included. INTRODUCTION 4H-l,4-Benzothiazines constitute an interesting class of heterocycles. They are anticipated to exhibit pharmacological activities (1,2). These are used as central nervous system depressants, antispasmodics, antiulcer, antidermatosis, antiinflammatories, antihistaminics etc. Besides pharmacological activities, they are having industrial applications (3). Some benzothiazines have shown significant effects against cancer (4,5). A slight change in substitution pattern in benzothiazine nucleus causes marked difference in their activities. Therefore, we have synthesized some hitherto unknown title benzothiazines to make them available for biological screening. RESULTS AND DISCUSSION The title benzothiazines have been synthesized by 2-amino-3-methyl / 5methylbenzenethiols which were prepared by the hydrolytic cleavage of 2-amino-4methy / 6-methylbenzothiazoles respectively by adopting the method reported elsewhere (6). 3,5-Dimethyl / 3,7-dimethyl-4H-l,4-benzothiazines (VIIa-h) have been synthesized by the condensation of ß-diketones (III) (viz. 3-bromo-benzoylacetone, 3methylbenzoylacetone, 4-ethoxybenzoylacetone or 4-ethylbenzo-ylacetone) with 2amino-3-methyl / 5-methylbenzenethiol (I) (Scheme 1) in dimethyl-sulfoxide which causes oxidative cyclization. Each reaction involves the formation of an intermediate enaminoketone (V). Under the experimental conditions 2-aminobenzenethiols (I) are readily oxidised to bis(2-aminophenyl)disulfides(II) which cyclizes to 4H-1,4benzothiazines (VII) by scission of sulphur-sulphur bond due to high reactivity of exposition of enaminoketone systems (III) towards nucleophilic attack.