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.
The preparation and the X-ray structure analysis of cis, trans, cis, cis-10-hydroxy-[4.5.5.5]fenestrane-1-methanol (8b) is reported. The measured bond angles and bond lengths of the central C(C)4 fragment are better reproduced by calculations with the AM 1 than by the MNDO method.