4H,l,3-Benzothiazin-4-ones

Reaction of 2-cyanomethyl-4H-l,3-benzothiazin-4-one with benzoylace-tonitrile at 160°C yielded 8-cyano-7-imino-9-phenyl-7//,ll//-pyrido[2,l-6][l,3]benzothiazin-l 1-one (85MI1 86MI2). Reaction of 2-ethoxy-2,3 dihydro-4//-l,3-benzothiazin-4-one with 1,2,3,4-tetramethylbutadiene and 2,4-dimethyl-l,3-pentadiene in the presence of boron trifluoride in diethyl ether gave rise to 6,7,8,9-tetramethyl- and 7,9)9-trimethyl-5a,6,9,ll-tetrahydropyrido[2,l-6][l,3]benzothiazin-ll-one, respectively (73JHC149). 

NaOH added to 2,3-dihydro-2-imino-4H-l,3-benzothiazin-4-one, heated several min. on a steam bath to effect complete soln., cooled to 0°, and ethylene oxide added —crude o-(2-hydroxyethylthio) benzoyl cyanamide. Y 90%. F. e. s. J. C. Howard, J. Org. Chem. 29, 761 (1964). 

Thiosalicylic acid added to dicyclohexylcarbodiimide whereupon an exothermic reaction takes place, dry benzene added to make the thickening mixture more fluid, allowed to stand 3 hrs. at room temp., then heated 20 hrs. on a steam bath 3-cyclohexyl-2-cyclohexylimino-2,3-dihydro-4H,l,3-benzothiazin-4-one. Y 56%. F. e. s. B. Loev and M. Kormendy, J. Org. Ghem. 27, 3365 (1962). 

Oxidation of 3-acyl-4-hydroxy-2H-l,2-benzothiazine 1,1-dioxide (9) in methanol by silver carbonate or terf-butyl hypochlorite produced 3-methoxy-4H-l,2-benzothiazin-4-one 1,1-dioxide (35),32 apparently by a free radical mechanism with participation of solvent. 

Ring closure with diazo compds. 2,3-Dihydro-4H-l,2-benzothiazin-4-one 1,1 dioxides... 

Formic acid added all at once at 21° to o-diazoacetyl-N-phenylbenzene-sulfonamide, and the product isolated after 5 min. 2,3-dihydro-2-phenyl-4H-l,2-benzothiazin-4-one 1,1-dioxide. Y 70%. Also with p-toluenesulfonic acid, and 2-methyl analog s. G. Heyes, G. Holt, and A. Lewis, Soc. Perkin I 1972, 2351. 

A soln. of 4-diloro-N-methyl-2-sulfamoylphenylacetic acid and a little p-toluene-sulfonic acid in dry toluene refluxed 1 hr. under a Dean-Stark trap -> 7-diloro-2-methyl-4H-l,2-benzothiazin-3(2H)-one 1,1-dioxide. Y 81%. F. e. s. J. G. Lom-bardino and E. H. Wiseman, J. Med. Chem. 14, 973 (1971) with PCI5 s. P. Catsou-lacos, J. Heterocyclic Chem. 8, 947 (1971). 

Benzo-l,4-thiazines and Related Compounds.— The chemical behaviour of the Vilsmeier product (111), derived from l,4-benzothiazin-3(4H)-one, has been the subject of detailed studies. Hydrolysis under different conditions affords the acid (112), the aldehyde (114), or the chloro-aldehyde (113), depending on the method of hydrolysis. Treatment of the perchlorate of (111) with DMSO leads to the displacement of the chlorine atom to give the dimethylsulphoxonium derivative (115), while reaction with pyridine proceeds with selective attack at the aminomethylene function, yielding the pyridinium salt (116). This latter reacts readily with aniline in acetic acid medium to give, along with 2-formyl-3-anilino-l,4-benzothiazine (117), the anilinomethylene derivative (120), whose formation probably involves an intramolecular rearrangement of the intermediate pyridinium salt (118), as depicted. 

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