cis,cis,cis,cis-[4.5.5.5]Fenestrane 11 was prepared by a novel route. The energy hypersurface of some stereoisomeric and substituted [4.5.5.5]fenestranes and -fenestrenes was explored by DFT calculations. The impact of some structural modifications, which enhance the planarizing deformation in the central C(C)4 substructures are discussed.
The systematic description of planarizing distortions of tetracoordinate carbon is outlined and specifically discussed for C(C)4 moieties which form the central part of fenestranes. Recent synthetic developments of the preparation of stereoisomeric [4.5.5.5]fenestranes and [5.5.5.5]fenestranes are described. Transformations with the aim of increased planarizing distortions are presented. The interaction of Fe2(CO)9 with a fenestradiene led to three structurally well defined Fe-carbonyl complexes.