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 r eadily available intermediate 3 allowed the electron-diffraction analy sis of 2. This structure analysis revealed long C-C bonds in the centr al C(C)4 fragment and a twist-envelope conformation for the four cyclo pentane 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-degrees with the remaining four being 103.7 +/- 0.2-degrees.