Dithietane oxides

Tire reaction of 1,3-dithietanes 14 with OXONE produced dithiirane 1-oxides 15 directly (95TL1867). Dithiirane 1-oxides 15 would be formed through the initially formed 1,3-dithietane oxides. 

The structures of four-membered rings are of considerable interest, owing in part to the low-frequency ring puckering vibration203. The comparison of the structures and conformational preferences of thietane oxides and dioxides discussed above with those of dithietane oxides and dioxides is therefore appropriate and will follow. 

FIGURE 1. Sulfur lone-pair and %<, ionization patterns in 1,3-dithietane, thietane oxide and 1,3-dithietane oxide. 

Dithietane oxides, Thietane oxides, Thiete oxides... 

Dithienothiophene dioxides, ESR spectra of 1050, 1051 Dithietane oxides formula of 382 PE spectra of 436 Dithietanes, perhalogenated 446 Dithietane tetroxides formula of 382... 

The preparation and investigation of the thietane oxide system (5a) is largely associated with stereochemical and conformational studies . The investigation of the thietane dioxides (5b) is substantially related to the chemistry of sulfenes , the [2 -I- 2] cycloaddition of which with enamines is probably the method of choice for the synthesis of 5b . The study of the thiete dioxide system (6) evolved, at least in part, from the recognition that the unstable thiete system 183 can be uniquely stabilized when the sulfur in the system is transformed into the corresponding sulfone , and that the thiete dioxide system is very useful in cycloadditions and thermolytic reactions. The main interest in the dithietane oxides and dioxides (7) appears to lie in the synthetic challenge associated with their preparation, as well as in their unique structural features and chemical behavior under thermolytic conditions . ... 

The conversion of cyclic sulfides to sulfones is accompbshed by more energetic oxidations. Perhalogenated thiolanes [106] and 1,3-dithietanes [107] are oxidized to sulfones and disulfones, respectively, by a mixture of chromium trioxide and nitric acid (equation 98) The same reagent converts 2,4-dichloro-2,4-bis(tnfluoromethyl)-l,3-dif/u cto cs to disulfone derivatives [107], whereas trifluoromethaneperoxysulfonic acid converts the starting compound to a sul-fone-sulfoxide derivative [2(equation 99). 

A one-pot synthesis of alkyl perfluoroalkyl ketones has been developed. Phosphoranes, generated in situ, are acylated with a perfluoroacyl anhydnde, and the resultmg phosphonium salts are hydrolyzed with alkali [4S (equation 48) Hydrolysis of a carbon-sulfur bond in 2-chloro-2,4,4-trifluoro-1,3-dithietane-S-trioxide, which can be obtained from 2,2,4,4-tetrachloro-l,3-dithietane by fluor-mation with antimony trifluoride followed by selective oxidations, opens the nng to produce 2-chloro-1,1,2-trifluorodimethyl sulfone [49] (equation 49)... 

Propanethial 5-oxide (78), the lachrymatory factor of the onion, functions as both a 1,3-dipole and a dipolarophile to give the first isolab le 1,2-dithietane 77, produced by rearrangement of the initially formed unstable... 

Similarly, a series of thial 5-oxides 83 dimerized upon standing to give 1,2-dithietane 1,1-dioxides 84, which were reduced to the corresponding alkenes on treatment with LiAlFLt (93SL839 96BSF515). 

Tlie thioketone 5-oxide 85, generated from allene 86 and SOCk in situ, decomposes to give the alkene 87. A mechanism, involving the transient formation of the 1,2-dithietane 88 (by dimerization of 85 followed by rearrangement), was proposed (85AGE855). 

The gas-phase structure of 1,3-dithietane 1-oxide (189) has been determined from its microwave spectrum and the spectra of eight isotopic modifications192. The ring is puckered, the angle between the two CSC planes being 39.3° with the oxygen equatorial. 

TABLE 6. Bond lengths" and bond angles in selected thietane oxides R1 5(5 186) and 1,3-dithietane tetroxide... 

The three highest occupied orbitals of sulfoxides are the lone pairs ns and n0, as well as the 7iso bond210. The 1,3-dithietane 1-oxide adds a lone-pair ionization and destabilizes the n0 and nso radical-cation states compared with thietane oxide. According to a hyperconjugative MO model, the ns+ combination in 1,3-dithietane is destabilized by about leV relative to the basis orbital energy a(ns) due to the combination with the... 

Thermolysis of the dicarbamic acid silyl ester (CH2 N[SiMe3]C02SiMe3)2) gives the 1,3-diazetane derivative 26 <96JOM93>. Alkylation of the 1,3-dithietane tetraoxide 27 with a,co-dihaloalkanes yields the dispiro compounds 28 (n = 1-4) <95ZOR589>. The first 1,2-dithiete S-oxide 29 is reported <95TL8583>. 

It is difficult to decide whether the discrepancy between the calculated and experimental data is due to a different conformational preference of the thietane dioxides in the liquid and the solid phase, or to the crude approximations included in the Karplus-Barfield equation. However, the relationship between vicinal coupling constants and dihedral angles appears qualitatively valid in thietane oxides and dioxides, particularly if trends instead of exact values are discussed . At any rate thietane dioxides, 1,3-dithietane dioxides and tetroxides maintain either planarity or a slightly distorted average vibrating conformation with a low barrier to ring planarity . 

The flash vacuum pyrolysis of 1,3-dithietane 1-oxide has been observed to give sulflne (76JA1264) which has been isolated and characterized in a matrix (79JPC1890). 

Dithietanes, dimers of thioketones, are best stabilized by electron withdrawing groups on the ring. They are oxidized to bis-sulfoxide derivatives quite readily, and in at least one case the intermediate dioxide was isolated (Scheme 29) (80AG(E)203). 

Thioaldehyde oxides are reported to be one of the lachrymatory agents in onions and are speculated to dimerize via an initial [4+2] cycloaddition to a five-membered ring that rearranges to a 1,2-dithietane dioxide. The latter has also been isolated from extracts of onions (80JA2490) and is reported to be the only characterized derivative of a 1,2-dithietane (Scheme 121). 

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