1,2,3-Dithiazoles and new routes to 3,1-benzoxazin-4-ones, 3,1-benzothiazin-4-ones and N-arylcyanothioformamides

Abstract

Treatment of methyl anthranilate with 4,5-dichloro-1,2,3-dithiazolium chloride 3 in dichloromethane at room temperature, followed by addition of pyridine, gave the imino derivative 7(R = Me) as expected; anthranilic acid, however, gave 4-oxo-4H-3,1-benzoxazine-2-carbonitrile 5. If triphenylphosphine was added to the reaction mixture instead of pyridine, methyl anthranilate gave methyl N-(cyanothioformyl)anthranilate 12(X =o-CO₂Me) whilst anthranilic acid gave 4-oxo-4H-benzo-3,1-thiazine-2-carbonitrile 6. These differences are explained mechanistically. When anthranilic acid was treated with the dithiazolium chloride 3 without the addition of pyridine, the delicate imino derivative 4 of the free carboxylic acid could be isolated (60%). This when heated in boiling toluene gave the benzoxazinone 5 quantitatively, and with triphenylphosphine at room temperature it gave the benzothiazinone 6 quantitatively. These reactions provide a good route to benzo substituted 2-cyanooxazinones and 2-cyanothiazinones from the corresponding anthranilic acids. With triphenylphosphine in dichloromethane at room temperature the imines 11 in general (i.e. without an o-CO₂H group) gave the corresponding N-arylcyanothioformamides 12 in very high yields, thus providing a good route to these compounds in two mild steps from the corresponding anilines.