1.2.6- Thiadiazine-3,5-dione 1,1-dioxides

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]

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>. 

Examples of C- or N- acylations of the 1,2,6-thiadiazine 1,1-dioxide nucleus are rare. However, acylation of 2,6-dimethyl-4//-l,2,6-thiadiazine-3,5(2H,6//)-dione 1,1-dioxide (140 R = Me) with propionyl chloride in acetonitrile in the presence of triethylamine and magnesium chloride affords the 4-propanoyl derivative (141) (Scheme 10) <89BRP2213145>. 

Disubstituted 4//-l,2,6-thiadiazine-3,5(2//,6//)-diones (140) in the presence of piperidine readily undergo Knoevenagel type condensation with a variety of aldehydes to yield the 4-arylidene derivatives (144) (Scheme 10) <92AP(325)509>. In contrast, however, the corresponding base-catalysed condensation with 3,5-diamino-4//-l,2,6-thiadiazine-l,1-dioxide (145) is successful only with 5-nitrofuran-2-carbaldehyde (145)->(146) (Equation (13)). 

EJM497> and 2,6-diphenyl-4-butyl-4/7-l,2,6-thiadiazine-3,5(2/7,6//)-dione 1,1-dioxide (300) <87CJC298> are reported to have antiinflammatory activity comparable to that of phenylbutazone. 

Decarboxylation of P-keto-esters is facile in aqueous DMSO, but in less reactive cases decarboxylation is accelerated by sodium chloride. Condensation reactions of dibenzocycloheptadienone (334) with aromatic aldehydes have been reported. Syntheses of the heterocyclic carboxylic acids (335) have been described. No effect of the heterocycle s ring current on the chemical shifts of the methylene protons could be detected in the n.m.r. spectrum of the nonamethylene-thiadiazine dioxide (336), which was prepared from cyclododecane-l,3-dione. ... 

C3H5KN2O5S, Potassium 2H-1,2,6-thiadiazine-3,5(4H,6H)-dione 1,1-dioxide monohydrate, 44B, 353... 

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