1.3- Dithietane ring

Ab initio calculations have also been carried out <2003JFC(124)99> for the photodimerization reaction of trifluoro-thioacetyl fluoride 13 which affords approximately equal amounts of trans- and >-2,4-difluoro-2,4-bis(trifluoromethyl-1,3-dithietane) 14 (Scheme 1) <1965JOC1375>. The calculations indicate that both dimers are thermodynamically stable relative to the monomer, and of almost equal stability. The Ec and G2gs.is values obtained in the G3(MP2) calculations of the dimers relative to monomers gave 115 and 45 kj mol-1 for cis-14, while the corresponding values for trans-14 were 112 and 44 kj mol-1. For both isomers, the 1,3-dithietane ring was found to be planar <2003JFC(124)99>. 

According to both HF and MP2 calculations on 1,3-dithietane, the geometry of the 1,3-dithietane ring in tram-16 is almost identical to that of the parent 1,3-dithietane 15, while this ring in cis-16 is slightly puckered with one C-atom 9.9° out of the plane formed by the other C-atom and the two S-atoms <2004MI111>. 

Without additional reagents 1,3-Dithietane ring opening... 

Dimerization and analogous cycloadditions of thiocarbonyl compounds also lead to 1,3-dithietans. Adamantanethione on irradiation or on treatment with methanesulphonic acid gave the dimer, containing a 1,3-dithietan ring, and 2-isopropylidene-5,5-dimethyl-6-oxo-l,3-oxathian-4-thione also dimerized on irradiation. Bis(trifluoromethyl)thioketen reacted with a variety of thiocarbonyl compounds, including isothiocyanates, to give 2-(hexafluoroisopropylidene)-l, 3-dithietan derivatives. ... 

Dicyanomethylene-l,3-dithietane rings open with nucleophiles with retention of both sulfur atoms and, while NaH produces hydrogen, the anion does not alkylate (Scheme 46) (64JOC497). 

Tlie present chapter reviews the chemistry of three- and four-membered ring compounds containing an S—S bond in their ring. Dithiiranes 1,2-dithietanes and 1,2-dithietes are the compounds of this type. Although 1,3-dithietanes are four-membered heterocycles which are prepared much more easily and are seemingly more familiar, they have no S-S bond in the ring and hence are not included in this chapter. 

H321). Tliese radical cations exist in a nonplanar conformation. With fra s-3,4-dimethyl substituents, the barrier to ring flip was estimated to be >5 kcal/mol. In connection with reactions of thiirane with the thiirane radical cation, ab initio calculations were reported on the 1,2-dithietane radical cation (93JA12510). 

Progress in the chemistry of three- and four-membered rings containing two sulfur atoms has been rapid in the past few years. An updated survey of the chemistry of dithiiranes, 1,2-dithietanes, and 1,2-dithietes is now provided from a major center in this area by Professor J. Nakayama and Dr. A. Ishii (Saitama University, Japan). 

To date, all saturated and unsaturated three- and larger-membered ring sulfones and sulfoxides (e.g., thiirane (3), thiirene (4), thietane (5), thiete (6), dithietane (7), thiolane (8), thiolene (9), thiane (10), thiene (11), dithiane (12), thiepane (13), thiocane (14), and their unsaturated analogues as well as isomers and closely-related systems) have been synthesized and their chemistry well-established. 

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. 

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. 

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 . 

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