Monocyclic Seven‐Membered Rings Containing Sulfur

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

“…This energy difference is much larger than for the oxygen homologues, because three-membered rings accommodate sulfur better than oxygen [ 40 ]. Nonetheless, bicyclic 6 has never been isolated, probably due to the low activation barrier for sulfur extrusion [ 40 , 48 , 70 ], which occurs through a sequence of low-energy processes involving several sulfur-containing intermediates [ 71 – 72 ].…”

“…2 ), a relatively simple and thermally stable thiepine was obtained, allowing experimental studies of its chemical and physical properties [ 75 ]. A single-crystal X-ray analysis showed 17 to be less curved (α = 49.6° and β = 28.0°) [ 70 ] than the computed structure of cyclohepta-1,3,5-triene ( 1 ; α = 52.9°, β = 25.4°) [ 14 ]; The MP2/6-31G(d) optimized geometry of the parent thiepine ( 5 ) (α = 50.3° and β = 30.8°) [ 40 ] is similar to that of the molecular structure of 17 [ 76 ]. Benzannulation of the thiepine ring on both sides results in the thermally robust dibenzo[ b , f ]thiepines, which are of interest for their potent biological activity, illustrated by the psychosedative and antipsychotic properties of zotepine ( 18 ; Fig.…”