1.2.4.6- Thiatriazine

The analogous sulfur-containing ring system, 1,3,4,5-thiatriazine, is also prepared by a ring expansion reaction (80JOC2604). Reaction of diphenylthiirene dioxide (255) with lithium azide in acetonitrile gives, among other products, the thiatriazine (14). The proposed... 

A new and unexpected synthesis of the 1,3,4,5-thiatriazine ring system is given by the treatment of substituted 1,2,3-thiatriazolium-l-imides with dry hydrogen sulfide. The mechanism suggested for this transformation is shown in Scheme 6 [94JCR(S)350],... 

Thiatriazines 1 and 1,3,4,5-thiatriazines 2 are not naturally occurring compounds. The compounds, originally 3 regarded as 2,4,5-trisubstituted 2//-l,2,3,6-thiatriazines 1 were subjected to 13C NMR spectroscopy and crystallographic scrutiny4,5 and shown to possess the structure of symmetrically 2,6-disubstituted 1,3,4,5-thiatriazines 2. In 1980. the first example of a 1,3,4,5-thiatriazine was reported in the oxidized sulfone form 3, formed by the reaction of 2,3-diphenylthiirene 1,1-dioxide with azide ion6 in very low yield. 

Compounds 2 are obtained as pale-yellow or orange crystals, not stable in acidic solutions. An X-ray crystal structure determination of 2,4,6-triphenyl-4//-l,3,4,5-thiatriazine shows a boatshaped 1,3,4,5-thiatriazine ring with equatorial orientation of the substituents.7 The nomenclature of the thiatriazines 1-3 is based on the 1UPAC rules and Chemical Abstracts.1,2... 

The 1,3,4,5-oxa- and 1,3,4,5-thiatriazine ring systems (and also the 1,2,3,5-tetrazines) are 8tc six-atom rings and thus do not obey the Huckel 6tc electron rule for aromaticity. Both ring systems adopt a boat-shaped conformation with the substituents on the N-4 atom taking up equatorial positions (Figure 1). 

The notable feature of the 1,3,4,5-thiatriazines (15 X = S) is their ready desulfurization with ring contraction, to yield 1,2,3-triazoles. Even chromatography on alumina is sufficient to cause desulfurization, but MCPBA is more effective <90JCS(Pl)2527>. 

The NMR spectrum of 1,3,4,5-thiatriazines 45 (At = substituted Ph) showed only nine signals due to the... 

Thiatriazines. Ring transformation of 4,5-diaryl-l,2,3-triazolium-A-aryl imides with H2S (Scheme 47) - good yields of 2,4,6-triaryl derivatives only. 

The thermodynamic stabilities of three possible annular tautomers of the parent 1,2,4,5-thiatriazine 134 were compared using ab initio HF/6-31G calculations (OOJOC931). The 4H isomer 134a appears to be the most stable (it is more stable than 134b by 11.6 kcal/mol and more stable than 134c by 15.5 kcal/mol), presumably because it allows low-energy distortion from planarity and formation of the boat conformation. 

The 1,2,4,6-thiatriazine system is the most common in all the oxa- and thi-atriazine series, and some investigations of the tautomeric behavior of 1,2,4,6-thiatriazine 1,1-dioxides 135, which can exist as N[2(6)]H 135a and N(4)H 135b tautomers (Scheme 39), have been performed. 

The parent thiatriazine 135 (R = H) exists predominantly in the 4H form 135b, as shown by its H NMR spectrum or by comparing its and N NMR data with... 

The pyrido[l,2,4,6]thiatriazine-5(6/7)-one 1,1-dioxide 2 was found to be useful in the treatment of nitric oxide synthase-mediated diseases and disorders <1996W018617>. 

Synthesis of pyrazolo[l,2-f][l,2,3,4]thiatriazine was discussed in CHEC-II(1996) <1996CHEC-II(8)747> and no article dealing with this subject has been published since. 

Reactions of arylchloromethyl-p-tolyl sulfoxides with tetrasulfur tetranitride (S4N4) yield 3,5-diaryl-1,2,4,6-thiatriazine 1-oxides <00T7153>. [4+2] Cycloadditions of thiazyl... 

Eight ring systems pyrazolo[3,2-r/][l,2,3,5]tetrazine 1, imidazo[5,l-r7][l,2,3,5]tetrazine 2, imidazo[l,2-A [l,2,4,5]-tetrazine 3, 4//-imidazo[5,l-r7][l,2,3,5]thiatriazine 4, 4//-pyrazolo[5,l -, whereas research on the other four has appeared only recently. In several cases, partially saturated forms of these rings have been obtained. The most substantial literature relates to derivatives of ring system 2 because of the antitumor activity of these compounds. 

X-Ray structure analysis of the recently synthesized pyrazolo[ 1,2,3,5]thiatriazine derivative 10 (Scheme 3) (cf. Section 11.20.7.2) has been carried out <2004SL2037>. The crystalline form of 10 proved to be nearly planar, and the five-membered and the six-membered rings made an angle of 1.68°. 

Dialkyl phosphoramidates react with sulphonyl di-isocyanate to give the phos-phorylated thiatriazine dioxide derivatives (33),28 while TMPT and formaldehyde together afford l,5-dioxo-2,4,6,8,9,ll-hexakis(methylamino)-l,5-diphosphabicyclo-[3,3,3]undecane (34).28... 

Of the thiatriazines, the 1,2,4,6-system has been the most studied. There has been particular interest in TV-alkyl-1,2,4,6-thiatriazine 1,1-dioxides because of their herbicidal, fungicidal, and histamine H2-antagonist activity (86TL123,87S170). The preparation of l-chloro-l,2,4,6-thiatriazines (576) by reaction of imidoylamidines (575) with an excess of sulfur dichloride was reported (80JOU1303). 

Sulfonyl diisocyanate gives the thiatriazine (577) on treatment with ammonia (58CB1200). Ketones and 86% hydrogen peroxide give 3,3,6,6-tetrasubstituted 1,2,4,5-tetroxanes (578) (80JCR(S)35). 

Reaction of 1,2,4,5-tetrazines (39) with AMhionitrosodimethylamine (217) and N-sulfinylanilines (218) led to the isolation of 4-dimethylamino-4// -1,2,4-triazoles (219) and 4-aryl-4//-1,2,4-triazoles (220), respectively. The formation of these products was explained by a [4 + 2] cycloaddition to give bicyclic intermediates, then elimination of nitrogen to yield the 1,2,4,5-thiatriazines, which form the products by extrusion of sulfur and sulfur oxide, respectively (Scheme 12) (79CZ230, 77AP269). 

N-Sulfinylamines are useful N—S two-atom fragments and react readily with a-ketoketenes to give l,2,3-oxathiazin-4-one 2-oxides (77JCS(P1)904,79CB1012). Reaction with azoalkenes gives 1,2,3,6-thiatriazines (77S305) as shown in Scheme 23. 

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