Dioxin, 1,4-Dithiin, 1,4-Oxathiin

The parent compounds 1,4-dioxin 1 and 1,4-dithiin 2 are known 1,4-oxathiin 3 is not known. 

X-Ray analysis (e.g. 2 bond lengths C=C 129 pm, C-S 178 pm bond angles C-S-C 100.2°, S-C-C 122.6° and 124.4°) shows that the systems 1 and 2 have the planar geometry of a slightly distorted hexagon. The NMR data (e.g. H-NMR, 1 5 = 5.50, 2 5 = 6.13) prove 1 and 2 to be a cyclic vinyl ether and a vinyl thioether, respectively, with no ring current effects. 

X-Ray crystal analyses of the dibenzo derivatives dibenzo[ 1,4] dioxin 4, thianthrene 5 and phenox-athiin 6, show that 4 is planar but that 5 and 6 have a folded structure. 

Among the reactions of 1,4-dioxins and 1,4-dithiins, oxidation of their tetraphenyl and dibenzo derivatives is important. This reaction leads to the formation of radical cations 7 and dications 8 

Tetraphenyl-1,4-dioxin, with SbCl5, forms a blue-violet radical cation. On further oxidation, a green dication is obtained. However, tetraphenyl-1,4-dithiin with SbCl5 yields a violet dication as a hexachloroantimonate. The dications 8 can be regarded as Huckel aromatic 67c-systems, in contrast to the antiaromatic parent compounds 1-3. 

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The UV photoelectron spectra of 1,4-dioxin, 1,4-dithiin, 1,4-oxathiin, and their dibenzo derivatives as well as the saturated compounds were detailed in CHEC(1984) <1984CHEC(3)958>. 

Dioxins, Oxathiins, Dithiins, and their Benzo Derivatives ... 

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