Editing Cubane (section)

==Synthesis==
The classic 1964 synthesis starts with the conversion of [[2-cyclopentenone]] to 2-bromo[[cyclopentadienone]]:<ref name="eaton-1964"/><ref name=eaton1964 />

[[File:Cyclopentenone to 2-bromocyclopentadienone.png|500px|class=skin-invert]]

[[Allylic]] [[bromination]] with [[N-Bromosuccinimide|''N''-bromosuccinimide]] in [[carbon tetrachloride]] followed by addition of molecular bromine to the [[alkene]] gives a 2,3,4-tribromocyclopentanone. Treating this compound with [[diethylamine]] in [[diethyl ether]] causes [[elimination reaction|elimination]] of two equivalents of [[hydrogen bromide]] to give the diene product.

[[File:CubaneSynthesis.png|thumb|left|500px|Eaton's 1964 synthesis of cubane]]{{clear left}}

The construction of the eight-carbon cubane framework begins when 2-bromocyclopentadienone undergoes a spontaneous [[Diels-Alder reaction|Diels-Alder dimerization]]. One ketal of the [[Endo-exo isomerism|''endo'' isomer]] is subsequently selectively deprotected with aqueous [[hydrochloric acid]] to '''3'''.

In the next step, the ''endo'' isomer '''3''' (with both [[alkene]] groups in close proximity) forms the cage-like isomer '''4''' in  a [[photochemical]] [2+2] [[cycloaddition]]. The [[haloketone|bromoketone]] group is converted to ring-contracted [[carboxylic acid]] '''5''' in a [[Favorskii rearrangement]] with [[potassium hydroxide]]. Next, the thermal [[decarboxylation]] takes place through the [[acid chloride]] (with [[thionyl chloride]]) and the [[tert-butyl|''tert''-butyl]] [[perester]] '''6''' (with [[Tert-Butyl hydroperoxide|''tert''-butyl hydroperoxide]] and [[pyridine]]) to '''7'''; afterward, the acetal is once more removed in '''8'''. A second Favorskii rearrangement gives '''9''', and finally another decarboxylation gives, via '''10''', cubane ('''11''').

A more approachable laboratory synthesis of disubstituted cubane involves bromination of the ethylene ketal of [[cyclopentanone]] to give a tribromocyclopentanone derivative.  Subsequent steps involve dehydrobromination, Diels-Alder dimerization, etc.<ref>{{Cite journal|doi=10.1071/C97021|title=Dimethyl Cubane-1,4-dicarboxylate: A Practical Laboratory Scale Synthesis|year=1997|last1=Bliese|first1=Marianne|last2=Tsanaktsidis|first2=John|journal=Australian Journal of Chemistry|volume=50|issue=3|page=189}}</ref><ref>{{Cite web|author =Fluorochem, Inc|date=July 1989|title=Cubane Derivatives for Propellant Applications|url=https://apps.dtic.mil/sti/pdfs/ADA210368.pdf|url-status=live|archive-url=https://web.archive.org/web/20210709185435/https://apps.dtic.mil/sti/pdfs/ADA210368.pdf |archive-date=2021-07-09 }}</ref>

[[File:Cuban4.svg|Alternative synthesis of a disubstituted cubane|555x555px|class=skin-invert|center]]
The resulting cubane-1,4-dicarboxylic acid is used to synthesize other substituted cubanes. Cubane itself can be obtained nearly quantitatively by photochemical decarboxylation of the thiohydroxamate ester (the [[Barton decarboxylation]]).<ref>{{Cite journal |last=Eaton |first=Philip E. |date=1992 |title=Cubane: Ausgangsverbindungen für die Chemie der neunziger Jahre und des nächsten Jahrhunderts |url=https://onlinelibrary.wiley.com/doi/10.1002/ange.19921041105 |journal=Angewandte Chemie |language=de |volume=104 |issue=11 |pages=1447–1462 |doi=10.1002/ange.19921041105|bibcode=1992AngCh.104.1447E |url-access=subscription }}</ref>