Oxathiins, and Thiazines

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.  

4-Dithiin (108), an isomer of (107), has been studied theoretically mainly in the form of its dibenzo-derivatives or their hetero-analogues (109a— c). o Phenoxathiin (109a), thianthrene (109b), and phenothiazine (109c) 

Kamiya and Y. Akahari, Chem. and Pharm. Bull. (Japan), 1972, 20, 117. 

Tyutyulkov, D. Simov, and S. Stojanov, Compt. rend. Acad. bulg. ScL, 1970, 23, 1095 A. F. Pozharskii and E. N. Malysheva, Khim. geterotsikl Soedinenii, 1970, 103. 

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