page_title: Fenestrane
section_title: Synthetic approaches
hierarchical_section_title: Fenestrane / Synthetic approaches
caption_attribution_description: AzaFenestraneSynthesis
context_page_description: 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. They can be regarded as spiro compounds twice over. Because of their inherent strain and instability, fenestranes are of theoretical interest to chemists. The name—proposed in 1972 by Vlasios Georgian and Martin Saltzman—is derived from the Latin word for window, fenestra. Georgian had intended that "fenestrane" solely referred to [4.4.4.4]fenestrane, whose skeletal structure looks like windows, and Kenneth B. Wiberg called that specific structure "windowpane". The term fenestrane has since become generalized to refer to the whole class of molecules that have various other ring-sizes. Georgian recommended rosettane for the class, based on the structural appearance as a rosette of flowers.
context_section_description: In one study, a [4.5.5.5]fenestrane was synthesized with one carbon atom replaced by nitrogen because aza- compounds and their salts are more likely to form crystalline compounds suitable for X-ray analysis than low-molecular-weight alkanes. In step 1 the alkyl halide 1-iodo-3-butene 1 is converted to a cyanozinc cuprate 2 (by transmetalation of the organozinc iodide with copper cyanide) which reacts in the next step with 1-nitrocyclopentene 3 in a nucleophilic addition whereby the nitronate 4 is captured by phenylselenenyl bromide to the selenium intermediate 5. Hydrogen peroxide oxidation of 5 yields the nitroalkene 6 as a mixture of syn and anti isomers. A [4+2]cycloaddition with n-butylenol ether in presence of trimethylaluminium gives the nitronate 7 and a second [3+2]cycloaddition by heating in presence of potassium carbonate gives the nitroso acetal 8. 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.
  In the borane salt the N–C–C bond angle is 126°.
  One study describes an unusual 8π disrotatory – 6π conrotatory electrocyclic cascade reaction aiming to minimise the number of steps required to synthesise a fenestrane.
caption: Azafenestrane synthesis 2006
exif: {}