PLANOID DISTORTIONS IN BRIDGED SPIROCOMPOUNDS FORMATION OF (ALL-CIS)-FENESTRANE IN THE ATTEMPTED SYNTHESIS OF THE (CIS,CIS,CIS,TRANS)-ISOMER

Article abstract of DOI:10.1016/S0040-4020(01)87585-2

Molecular distortions in bridged <4.4>spirononanes and fenestranes are discussed in terms of symmetry deformation coordinates.This analysis reveals that the central, quaternary carbon atom in most of these compounds shows mainly a decrease of the two opposite ring bond angles, whereas the distortions in fenestranes are dominated by an increase of the two opposite bond angles.Dicyclopentadienone 8 serves as the starting material for the preparation of <5.5.5.5>fenestranes.In the key step of the synthesis, the Pd-catalyzed reductive transannular reaction of the enaminonitrile 13 and the ketolactone 17, (all-cis)-<5.5.5.5>fenestrane 6 is formed instead of the (cis,cis,cis,trans)-isomer 7.