Fenestrane

A fenestrane in organic chemistry is a type of chemical compound with a central quaternary carbon atom which serves as a common vertex for four fused carbocycles.

The smallest member of the family, consisting of four fused cyclopropane rings, is [3.3.3.3]fenestrane, which has systematic name tetracyclo[2.1.0.01,3.02,5]pentane and is also called pyramidane.

In an extreme case[clarification needed] the central carbon atom, which would ordinarily have tetrahedral molecular geometry for its four bonds gets completely flattened.

If the central carbon were to be tetrahedral, it would have the form of spiropentadiene, but with additional bonds between the two cyclopropyl rings rather than double-bonds within them.

The analogous germa- and stannapyramidanes, with trimethylsilyl groups bonded to the corners, Ge[C4(SiMe3)4] and Sn[C4(SiMe3)4] on the other hand have been synthesised.

Hydrogenation with Raney nickel gives the diol 9 which on a double Mitsunobu reaction (with an amine proton donor) gives the azafenestrane 10 as the borane salt.

One study describes an unusual 8π disrotatory – 6π conrotatory electrocyclic cascade reaction aiming to minimise the number of steps required to synthesise a fenestrane.