1.2- Dithiete theoretical studies

Very recently a theoretical study of the tautomerism between 1,2-dithiins and dithiones was published139. Contrary to 1,2-dithiete, 1,2-dithiin (34a) is a nonplanar heterocycle with an energy barrier of inversion via the fully conjugated planar structure of 8.3 kcal mol 1, estimated attheMP2/6-31G(d) level. Similarly to what was found for 1,2-dithiete with respect to 1,2-dithioglyoxal, the cyclic unsubstituted 1,2-dithiin is predicted to be about 15 kcal mol 1 more stable than the open-chain dithiones (34b-34d). 

There are some theoretical studies concerning the stability of 1,2-dithietenes and ethane-1,2-dithiones <1996IJQ859>. The valence isomerization of a series of 1,2-dithietes 19 to the open-chain dithiones 20 was studied by CASSI multiconfiguration methods, including the CASPT2 perturbational treatment <1996IJQ859>. 

Theoretical studies on the ring-opening reaction of 1,2-dithiete by using unrestricted density functional theory (DFT) with fractionally occupied frontier orbitals were reported. The topic addressed in these studies was the question of the relative energies of the sulfur species 1,2-dithiete 19a and dithioglyoxal trans-20a <1999JCP7705>. 

Formal substitution of two benzene double bonds by sulfur atoms leads to the four-membered heterocycle 1,2-dithiete (37). This compound has not been synthesized, although derivative 38 is known,59,80 and dicyano-l,2-dithiete (39) is very probably an intermediate in some reactions of thiacyanocarbons (see below). Models of both compounds have been studied theoretically,23,91 but the calculations are... 

Theoretical and experimental studies on the reaction of 3,4-bis(methoxycarbonyl)-1,2-dithiete with alkenes and alkynes yielding cycloadducts have been carried out. The activation energy of the interconversion of the 1,2-dithiete to 1,2-dithione was estimated by MO calculations. These calculations (MP2/6-31G(d)) show that the dithiete 19f is 5.8 kcal mol-1 more stable than the ethane-1,2-dithione cis-20f, and the tautomerization energy is 28.5 kcal mol-1 from the thiete 19f and this value of the activation energy supports the possibility of the tautomerization between the 1,2-dithiete 19f and ethane-1,2-dithione cis-20f, at least at high temperature <1996IJQ859>. 

MO calculations of the reaction of 3,4-bis(methoxycarbonyl)-l,2-dithiete (150) with alkenes to produce 2,3-dihydro-1,4-dithiins (152) confirmed that the reaction is a reverse-electron-demand hetero-Diels-Alder type between the valence isomer 1,2-bis(methoxycarbonyl)ethane-l,2-dithione (151) and the dienophiles (Scheme 58). Sulfur dioxide has been shown to promote its hetero-Diels-Alder and chelotropic additions to 1,2-dimethyUdenecyclohexane. The competition between hetero-Diels-Alder and chelotropic addition of sulfur dioxide with substituted 1,3-dienes has been investigated by studying the theoretical and experimental effects on the relative stability of sultines and sulfolenes. ... 

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See also in sourсe #XX -- [ , ]

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