Thiepin, theoretical studies

Theoretical studies on thiepine-thianorcaradiene (benzene sulfide) valence isomerization have been of continuous interest. In addition, hypervalency of sulfur in thiepines has been theoretically studied. The interest in fused systems, such as dibenzo[/)/]thiepines, toward pharmacologically active compounds is growing. In the last decade, many reports on the synthesis, characterization, and utilization of enantiomerically pure dihydro- and tetrahydrothiepines and thiepanes have appeared. 

The theoretical study of thicno[3,4-z/ thiepine 15 and furo[3,4-rf thiepine 16, as dienes in thiophene or furan moieties, respectively, in the Diels-Alder reaction was investigated with semi-empirical AMI calculations <1995JHC1499>. S-Methylation at the thiophene moiety of thieno[3,4-t/]thiepine 15 was predicted to lower the activation energy and facilitate reaction with less reactive dienophiles, such as ethylene. 

A theoretical study of thieno[3,4-rf]thiepine and furo[3,4-rf]thiepine as dienes in the Diels-Alder reaction has been published <95JHC1499>. 

Thiepines have been studied extensively due to theoretical and biological interest. The theoretical interest arises from whether thiepines with 8jt electrons are nonaromatic or antiaromatic. The subsequent interest is in thiepine-benzene sulfide valence isomerization. Because thiepines are generally thermally unstable and eliminate sulfur, the... 

Other theoretical tests of aromaticity have been studied. The graph theory has predicted thiepine to be antiaromatic <76JA2750>. A new measure of aromaticity has been studied on the basis of absolute hardness >]) known to be an index of stability and reactivity of a molecule. The operation formula is the equation, tj = (/-/l)/2 where / is the ionization potential and A the electron affinity. Alternatively, the equation is rj = (Fhomo- lumo)/2. Absolute hardness has also predicted thiepine (1) and 2-benzothiepine (5) to be antiaromatic and 3-benzothiepine (6) to be nonaromatic. However, the prediction by this approach fails for 1-benzothiepine (2) <89JA737l>. 

---