1,4-Oxathiin, structure

In this chapter, the structures and chemistries of 1,3-dioxins, 1,3-oxathiins, and 1,3-dithiins are described, including both their fully saturated forms (1, 7, and 13) as well as their benzo analogs (6, 11, 12, and 17). The formally fully unsaturated monocyclic structures (4, 9, 10, and 16) contain only one endocyclic double bond with further unsaturation being accomodated by exocyclic double bonds (2, 3, 5, 8, 14, and 15), for example, by the introduction of a carbonyl group. Well known and intensively studied are the Meldrum s acid derivatives 18 and 19. In addition, 1,3-dioxane, 1,3-oxathiane, and 1,3-dithiane moieties can be part of spiro structures as well as hi- and tricyclic analogs. And finally, both the structures and chemistries of the corresponding sulfoxides and sulfones are also reported. 

Many crystal structures of host compounds or solvate compounds with 1,4-dioxane as well as a wide range of organic structures bearing a 1,4-dioxin, 1,4-oxathiin, or 1,4-dithiin core have been determined by single crystal X-ray diffraction. 

Various dihydro-1,4-oxathiins and dihydro-1,4-dithiins are reported to be useful in areas other than agriculture. Thus, 2,3-dihydro-l,4-dithiin-5,6-dicarboximides display a wide spectrum of biological activity (77SST(4)332) while derivatives of the basic structure (243) have been patented as tranquilizers, anticonvulsants and hypnotics (76GEP2550163). Sedative, myorelaxant and cataleptic properties are associated with certain 2,1-benzoxathiane 2,2-dioxides (75BRP1383459). 

Mathre, D.E. (1971) Mode of action of oxathiin systemic fungicides. Structure-activity relations. J. Agric. Food Chem. 19(5), 872-874. McCall, P.J., Swann, R.L., Laskowski, D.A., Unger, S.M., Vrona, S.A., Dishburger, H.J. (1980) Estimation of chemical mobility in soil from liquid chromatographic retention times. Bull. Environ. Contam. Toxicol. 24, 190-195. 

Dihydro-2-methyl-l,4-oxathiin-3-carboxanilide (92), known as Carboxin (a fungicide), rearranges to the enamine (93) when refluxed in toluene with / -toluenesulfonic acid. The structural assignment of (93) are made on the basis of crystal x-ray diffraction analysis <84MI 609-02>. 

Whereas 1,4-dioxin is planar, 1,4-dithiin 173 and 1,4-oxathiin are significantly distorted from planarity [98JST11]. For 173 a planar nonequilibrium structure was computed to be destabilized by about 2.5 kcal/mol with respect to the boat con-former. The half-chair and boat conformations of 3,4-dihydro-l,2-dithiin, 3,6-dihydro-1,2-dithiin, 4//-l,3-dithiin, and 2,3-dihydro-1,4-dithiin 174 were investigated at the MP2/6-31G level [98JCC1064] (see the structures of the corresponding dioxines in Scheme 114). The half-chair conformers are stabilized with respect to the corresponding boat conformers, and the most stable structure was found to be the half-chair conformer of 174. 

Formatira and Chemical Properties.— The structure of one of the adducts obtained from azibenzil and sulphur dioxide has been determined to be an oxathiin instead of the thietan-3-(me 1,1-dioxide proposed earlier. Derivatives of 3-aminothietan 1,1-dioxide have been obtained by additicm of... 

Dithiins, Oxathiins, and Thiazines. Six-membered cyclic compounds with one or two sulphur atoms have a non-planar structure. Thus, in general, ir-type calculations take into account the twisting of the p,-orbitals. HMO and PPP calculations have provided a negative ir-bond order between the sulphur atoms in 1,2-dithiin (107). EHT calculations, however, predicted a (T-bond between the sulphur atoms. Consequently the cyclic structure should be more favoured than acyclic valence tautomers. This was supported by spectral data the weak long-wavelength absorption is thought to correspond to a ir <- ir transition of (107) rather than a ir n transition of acyclic thione structures. ... 

---