 Whereas the C–C bond in ethane is 155 pm, in this fenestrane, the bonds extending from the central carbon atom are shortened to 149 pm while those at the perimeter are lengthened to 159 pm.A diterpene called laurenene containing a [5.5.5.7]fenestrane ring system was the first natural fenestrane to be discovered.The first fenestrane ever synthesized was a [4.5.5.6]fenestrane