Sulfur-containing systems

Unlike the O—N-bond-containing heterocycles, the pivotal sulfur-containing systems can also rearrange by elimination of a small species, according to the generalized pathway 211 213 (Scheme 35). The reverse... 

Two thirds of the 34 possible systems containing at least one nitrogen atom and oxygen and/or sulfur are known and well described. Of these, six of the possible oxathiazines (Table 1) have been reported. A general feature of this and other sulfur-containing systems is that they are often only known with the sulfur atom in its higher oxidation states. Thus, for example, 1,2,5-oxathiazines are only known as the 2,2-dioxides. Of the six possible dioxazines (Table 2) only the 1,2,3-isomer is unknown. All six of the possible dithiazines... 

Analogous transformations are found in the corresponding sulfur-containing systems. Ring cleavage and rearrangement have been observed on irradiation of substituted thiolane-2,4-diones in the presence of base,175 whereas irradiation of thiolane-2,4-dione itself (215) in fluorosulfonic acid affords the novel 3-oxo-3//-l,2-oxathiole (216).176 The thioxanthene (217)... 

The only comparable sulfur-containing system investigated is that found in thiabenzene187 and thianaphthalene.188 In both cases, 1,2-aryl migrations have been observed on irradiation, as shown, for example, in the triphenyl-thianaphthalene (237). No evidence for any ring transposition reaction in these compounds has been reported. 

Since in many instances we shall try to compare the properties of thiocarbonyl compounds with their carbonyl analogs, we recall that, in general, the theoretical treatment of sulfur containing systems is more demanding, essentially because of the larger number of electrons in the sulfur atom. This has restricted the ab initio calculations to relatively small compounds or to the use of small basis sets. Until quite recently, high level ab initio calculations were only reported for a few, small thiocarbonyl systems. 

The isobutane yield was constant in both systems resulting in significantly higher iC /nC and iC /LPG volume ratios in the sulfur-free system. Although converting more of the feed, the sulfur-containing system produced significantly less C + C2 than the sulfur-free system. 

Sulfur-Containing Systems. Irradiation of S02, SF4, or SFe gives no observed volatile products. Sulfuryl fluoride on the other hand was found to produce a number of products these include 02, OF2, SFe, SOF4, and some species with the probable stoichiometric formula F2S04 (the compound FS02-00F is known). 

Obviously, [2,3]-sigmatropic rearrangements of sulfur-containing systems comprise a class of reactions with a considerable constitutional scope. But the configurational consequences of the concerted suprafacial reaction mode are even more exciting, both from a stereochemical point of view and for synthetic reasons. 

The alkaline hydrolysis of l,2-dithiol-3-ones is complex the reaction products1553 include the two sulfur-containing systems 107 and 108. 

Dianions derived from sulfur and oxygen containing polycyclic systems have not been reported until very recently. The weak carbon-sulfur bond could discourage attempts to prepare such dianions. Sulfur removal studies by alkali metals were successful due to the properties of the carbon-sulfur bond 182,183). Reductive alkylation studies on model compounds which are relevant to sulfur containing systems demonstrated the stability of hydrocarbon dianions 182). A spectroscopic study performed under mild conditions afforded the characterization of sulfur and oxygen containing dianions 184 186). Benzo[b]thiophene, (73), 1,3-diphenylbenzo[c]thiophene (74) and l,3-diphenylbenzo[c]furan (75) form the respective dianions at low temperature. 

It is interesting to note that sulfur containing systems, such as 2-thiophene methanol are successfully oxidised to the aldehyde with little evidence of catalyst poisoning by the sulfur (activities similar to non sulfur containing systems). Both Pt/C and Ru/C are active, but Ru/C retains a higher activity on recycle than the Pt/C catalyst (yields of 85/70/45 compared to 65/45/15 for 3 cycles), thus showing better poison resistance than the Pt/C catalyst. 

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