The structure of substituted spirans derived from benzo-1,5-dithiepine and benzo-1,5-dioxepine systems. Ring-reversal isomers

Structural studies of newly synthesized substituted spirans, derived from methyl- and tert-butylbenzenes, containing either 1,5-dioxepine or 1,5-dithiepine system are reported. Crystal structures of two representative compounds were determined by X-ray diffraction. One of spirans containing 1,5-benzodithiepine appears in two isomeric forms equivalent by inversion of both spirorings. Energy calculations were carried out to find the preferred conformations. For spiran with sulfur atoms, the minimum-energy conformation is virtually identical with that in the solid state, whereas for the 1,5-dioxepine system they are different. q 2003 Elsevier B.V. All rights reserved