1,3,2,4,6-Dithiatriazines

Weak interactions may occur between molecules (intermolecular association) as well as within a molecule (intramolecular) for chalcogen-nitrogen ring systems. This behaviour is especially significant for odd electron species, e.g., [EsNa]" (4.14, E = S, Se) and [PhCNaEa] (4.15, E = S, Se), both of which are seven r-electron molecules. As mentioned in the previous section, it also occurs for the eight r-electron dithiatriazines 4.10... 

Ab initio molecular orbital calculations for the model systems RCN3S2 (R = H, NH2) show that these dithiatriazines are predicted to be ground state singlets with low-lying triplet excited states (Section 4.4). The singlet state is stabilized by a Jahn-Teller distortion from C2v to Cj symmetry. In this context the observed dimerization of these antiaromatic (eight r-electron) systems is readily understood. 

Only a few reactions of benzodithiadiazines have been investigated. In common with dithiatriazines 12.8, the anti-aromatic system 12.12 (R = H) undergoes a reversible 5,5 -cycloaddition with norbornadiene. The reaction of 12.12 (R = F) with triphenylphosphine results in a ring contraction to give the imino 2 -phosphane 12.13. ... 

The polyazapolysulfur ring system 1,3,2,4,6-dithiatriazine 15 is obtained by reacting 1-aryl-2,2,2-trifluoroethanone oximes with tetrasulfur tetranitride in refluxing toluene. However, the yield is only moderate <%JHC295>. 

The molecular structure of the bicyclic framework in 108 is best described as a dithiatriazine bridged by an -N=S=N- group. The aryl-substituted derivatives 108 (R=aryl) form 2 1 inclusion complexes with aromatic fluorocarbons or hydrocarbons.266 In solution, the phenyl derivative 108 (R=Ph) is fluxional.258... 

The reactions of l-aryl-2,2,2-trifluoroethanone oximes 378 with tetrasulfur tetranitride (S4N4) in toluene at reflux gave 5-aryl-5-trifluoromethyl-4//-l,3,2,4,6-dithiatriazines 379, l-aryl-2,2,2-trifluoroethylideneaminosulfenamides 380 and sulfur (equation 165) . ... 

The NH groups of sulfonamide functions are also readily alkylated. The 1,2,6-thiadiazine dioxide (74) gives the 2-methyl derivative on treatment with iodomethane in acetone in the presence of potassium carbonate <65CI(L)182). The 1,3,2,4,6-dithiatriazine (75) forms a silver salt (64MI22800), and reaction of the salt with iodomethane gives the expected TV-methyl compound. 

Electrophilic sulfur species such as thionyl chloride are frequently used in the synthesis of sulfur-containing heterocycles and, for example, reaction with N-N 1,5-dinucleophiles is a direct route to 1,2,6-thiadiazine 1-oxides. Thus the thiadiazines (138 n-1) are readily prepared by treatment of (231) with thionyl chloride in pyridine (81JCS(Pl)l89l), and the benzothiadiazine (232) is similarly made from (233) (64JOC2717). Reaction of (234) with thionyl chloride gives the dithiatriazine (235) (74ZOR488). 

Thiadiazines can also be prepared from [3 + 3] condensations involving sulfur diimides. Thus reaction of bis(lV-tosyl)sulfur diimide (69TL4117) with 1,3-diaminopropane gives the thiadiazine (18). Bis(trimethylsilyl)sulfur diimide reacts with CSI to give a 1,3,2,4,6-dithiatriazine (74CB1,.74ZN(B)799) (Scheme 27). 

The only reported synthesis of a 1,2,3,4,6-dithiatriazine (256) involves the reaction of disulfur dichloride with a silatriazole (78ZC336). The product is described as a red-brown crystalline solid but no other data are given. 

The intensity and array of colors is consistent with similar observations for structural relatives such as the dithiazoles <1989CC1134>, dithiatriazines <1989CC96>, and dithiatetrazocines <1981JA1540, 1989J(P 1)2495, 1989CC1137>. Compounds 26-28 represent one example from each family. 

The disulfide bond in radical 35 and dimer 36 can incorporate atomic nitrogen, allowing a ring-expanded dithiatriazine dimer 53 (Scheme 1). Two mechanisms have been proposed for this plasma reaction with one involving the initial formation of compound 52 <1989JCD1705>. 

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