Synthesis and Electron-Diffraction Structure of all-cis-[5.5.5.5]Fenestrane

The efficient synthesis of all-cis-5.5.5.5]fenestrane ( 2 ) from the readily available intermediate 3 allowed the electron-diffraction analysis of 2 . This structure analysis revealed long C? C bonds in the central C(C)₄ fragment and a twist-envelope conformation for the four cyclopentane substructures. The four bridgehead H-atoms are in a synclinal rather than an ecliptic position with an approximate D₂ symmetry of 2 . Planarizing distortions are evident from the opposite bond angles at the central C-atom being 116.2 ± 0.5° with the remaining four being 103.7 ± 0.2°.