4H-thiazine

If the same reaction was carried out in refluxing EtOH using 0.5equiv. of NaOEt in the presence of oxygen, 3-alkyl-5,6-dihydro-4H-thiazine-2-carbonitrile 621 was formed in >90% yield [275],... 

The 3,4-dihydrothiazine-3-thione (236) is converted into the 2/f-thiazine (237) by direct. S-ethylation with triethyloxonium tetrafluoroborate. With methyl iodide S,JV-dimethylation occurs to give the thiazinium salt (238), deprotonation of which yields a 4H-thiazine (239) (69JHC247). 

Chemistry of important flavor compounds, viz., 2-acetyl-l-p)nToline, 6-acetyl-l,2,3,4-tetrahydropyridine, 2-acetyl-2-thiazoline, and 5-ace-tyl-2,3-dihydro-4H-thiazine 06CRV2299. 

Ethyl 9-ethoxycarbonyl- and 9-hydroxymethyl-3-methyl-6-oxo-2/f,6//-pyrido[2,l-Z>][l,3]thiazine-4-carboxylates were isomerized into 4H,6H-pyrido[2,l-b][l,3]thiazine-4-carboxylates by treatment with KOH overnight at room temperature and by treatment with NaOEt at 0 °C for 1 h and room temperature for 3h in EtOH, respectively. In another experiment, when the 9-hydroxymethyl derivative was treated with NaOEt in EtOH at — 10°C for 3h, a 2.5 1 mixture of ethyl 3,4-cw-H-9-ethoxymethyl-3-methyl-6-oxo-3,4-dihydro-2//,6//-pyrido[2,l-Z)][l,3]thiazine-4-carboxylate and the aforementioned 4//,6//-isomer were obtained (00JCS(P1)4373). 

Dihydro-2/7- 74 and -4//-l,2-oxazines and thiazines 75 are interrelated by prototropy, being enamines and imines, respectively. In the case of oxazines, the imine form 75 is favored, and there are several well established examples of this system, including the parent heterocycle 75 (X = O) [84MI2]. No tautomeric equilibrium between the 2H and 4H forms has been observed under normal conditions in solution or in the solid state. However, the formation of intermediate 2H isomers 77 was proposed both for the conversion of 3-phenyl-5,6-dihydro-4//-l,2-oxazine 76 (R = Ph, r = R = H) into 2-phenylpyrrole(89TL3471) under strong basic conditions and for thermal decomposition of cyclopentene-fused 1,2-oxazine 76... 

Chemical Name 2-(4-Chlorophenyl)tetrahydro-3-methyl-4H-1,3-thiazin-4-one 1,1-dioxide Common Name Chloromethazanone Structural Formula ... 

Dihydro-4H-l,3-thiazine werden durch Natriumboranat bei 0-10° in schwach sau-rer athanolischer Losung zu den Tetrahydro-1,3-thiazinen reduziert (vgl. S. 348)2 z.B. ... 

Bei Reduktion mit Natriumboranat in alkalischem Milieu wird der 5,6-Dihydro-4H-1,3-thiazin-Ring aufgespalten4. 

An asymmetric route to the 5,6-dehydro-4H-1,3-thiazine skeleton via an asymmetric /refero-Diels-Alder reaction [95]... 

B. 4H-1,4 -Thiazine 1,1-Dioxide. Caution This step should he carried out in a hood to avoid exposure to hydrogen chloride gas. 

Table 3 Enthalpies, entropies, and melting points of A/-aryl-4H-ben-zo[t/][1,3]thiazin-2-amines 71...

There is an example of a thiazine 174 which at room temperature is in equilibrium with the open-chain starting material 175 it was made from, and at 110°C additionally with thiazoline 176, which slowly decomposes at this temperature (Scheme 10) <1976CC366>. After 4h reflux and cooling, the solvent was removed and the mixture... 

Stirring a chloroform solution of 9a-amino-2-fm-butyl-4,6,7,8,9,9a-hexahy-dropyrido[2,l-b][l,3]thiazin-4-one at 35°C for 64 h afforded 2-tert-butyl-6,7,8,9-tetrahydro-4H-pyrido[l,2-fl]pyrimidin-4-one in 95% yield [89JCS(P1)1231]. 

H- 1,2-Oxazines are stabilized as 4,4-disubstituted derivatives but 4H- and 6if-l,2-thiazines are almost unknown. Possibly the paucity of these compounds simply reflects a lack of interest, for 6if-l,2-oxazines are comparatively common, and 3,5-diphenyl-6if- 1,2-oxazine, for example, is a stable crystalline solid. Similarly, cyano-1,2-oxazines (6 R=alkyl) are formed by the photolysis of azidopyridine oxides (5). However in the case where R3 = H, these products rearrange to pyrroles (7) (81CC36). 

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