1,2,6-Thiadiazine 1,1-dioxides structure

The single crystal X-ray structure of 3-methyl-4//-pyrido[2,3- ] l>2,4-thiadiazine 1,1,-dioxide 13 was compared to that of diazoxide 14 in order to determine the predominant tautomeric form and it was found that both these thiadiazine-dioxides exist in the AH tautomeric form in the solid state <1995AXG2064>. 

Other thiadiazine dioxides have been investigated (70CRV593). The 2//-tautomer (48) is favoured over the 4JT-tautomer (49) and structure (50) in which the tautomeric proton is on oxygen. The dihydro-1,2,6-thiadiazine dioxides are also thought to exist in the tautomeric equilibrium (51) i(52). 

Synthesis and structural studies of new 3-alkylamino-pyrido[43-e][l,2,4]thiadiazine 1,1-dioxides have been reported <99T5419>. 

Table 2 X-ray structure of bicyclic 1,2,6-thiadiazine-1,1-dioxide derivatives (25) and (26).

The nucleophilic substitution, amination, aldol-type condensation, oxidation, and hydrolysis of the l//-pyrazino[2,3-c][l,2,6]thiadiazine 2,2-dioxide system, structurally related to pteridine, were studied in detail <03HCA139>. Chlorinated pyrazines were directly oxidized to their corresponding iV-oxides using dimethyldioxirane in a completely regioselective fashion <03HEC221 >. 1,6-Dibenzoyl-5//, 10//-diimidazo[ 1,5-a 1, 5 -[Pg.374]

The oxidation of isothiazolium chlorides 135 with hydrogen peroxide in acetic acid at room temperature gave the 1,2,3-thiadiazine 1-oxides 408a,b in 15-51% yield. They were also converted into 1,2,3-thiadiazine 1,1-dioxides 409a-c in 16-43% yield. The structure 408b was confirmed by X-ray diffraction (00SUL109, Scheme 137). 

Formal condensation of a benzene ring onto a 1,3,4-thiadiazine, a 1,2,4-thiadiazine, a 1,2,6-thiadiazine, or a 1,2,5-thiadiazine leads to the benzothiadiazine structures G-J. Two benzo derivatives of 1,2,3-thiadiazines are known 1,2,3-benzothiadiazine (K) and 3,1,2-benzothia-diazine (L). Both benzo derivatives occur mainly as, S,S-dioxides for review articles see refs 1 and 2. 

Proton NMR spectroscopic and dipole moment measurements indicate that the heterocyclic ring of 5-amino-4,4-dibenzyl-47f-l,2,6-thiadiazin-3(2//)-one 1,1-dioxide (36) has the same planar structure in solution as in the solid state <88CJC2477>. 

Amino-4//-l,2,6-thiadiazin-3(2//)-one 1,1-dioxide (48) has a monoclinic crystal structure with a flattened boat conformation. The SOz prow and the 4-CHz stern subtend angles of 27.5° and 25.3°, respectively, with the planar hull as defined by Nj—C3—C5—<86AX(C)892>. Boat conformations have also been determined for 4//-l,2,6-thiadiazine-3,5(2//,6//)-dione 1,1-dioxides (49 R = cycloQH, or Ph) <87CJC298>. 

Likewise, A-methylsulfamide and 2-acetylcycloalkanones (243 n = 1 or 2) yield mixtures of the isomeric cycloalkano[l,2,6]thiadiazine 1,1-dioxides (244) and (245). However, with sulfamide the condensations are regioselective and with 2-acetylcyclopentanone (243 n = 1) yield exclusively the 2//-3-methyl derivative (246), whereas with 2-acetylcyclohexanone (243 n = 2) the 2/7-5-methyl derivative (247) is the sole product (Scheme 31) <94JCS(P2)i56l>. The structures of these products have been confirmed by detailed NMR spectroscopic data (see Section 6.16.4.2). 

Benzo[e]-l,2,4-thiadiazine 1,1-dioxide has been shown to prefer the AH-structure (432). A new, simple route to 3-oxo-derivatives of this system has been developed anilines are added to CSI (CSI is CISO2NCO) and the resultant N-chlorosulphonyl-ureas cyclized with AICI3. Yields are good to excellent, and... 

Several 1,2,3-thiadiazine 1-oxides were prepared in moderate yields by oxidation of 2-benzenesulfonylaminothia-zolium salts and the corresponding imines with hydrogen peroxide at 0° C (Scheme 4) <1999JHC1081>. The X-ray crystal structure of the 1,2,3-thiadiazine 1-oxide 27e, where R = R = CH3 and R = 4-Br, has also been reported. The structures of the products were confirmed by IR and H and NMR spectroscopy. Conversion of the 1,2,3-thiadiazine 1-oxides to the more common 1,2,3-thiadiazine 1,1-dioxides was achieved by treatment with meta-chloroperbenzoic acid (Scheme 4). 

N-Substitution at the N-3 position of the bicyclic thiadiazine 2,2-dioxide ring system 47 ( = 1, 2) produces a 6 ppm downfield shift of the methyl carbon. This observation should help with future structural elucidations <1995BMC179>. 

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