User:OrganoMetallurgy/Drafts/Pentaprismane

Pentaprismane is a polycyclic saturated hydrocarbon with D5h symmetry that is of theoretical interest due to its structure.

Synthesis
Pentaprismane's synthesis was first reported in 1981. Diels alder reaction between 1,1-dimethoxy-2,3,4,3-tetrachlorocyclopentadiene and p-benzoquinone, followed by [2+2] photocyclization, followed by dechlorination by refluxing with lithium in anhydrous ammonia then tert butanol in wet tetrahydrofuran, which also reduces the ketone groups to the endo endo dihydoxy derivative, followed by reaction with tosyl chloride in pyridine to produce the ditosylate, followed by reaction with sodium iodide in HMPA, to produce the mono and diiodide, followed by reaction with butyllithium to trigger elimination to produce the Dimethoxyhomohypostrophene, which photocyclizes to dimethoxyhomopentaprismane, acid catalyzed hydrolysis of the dimethoxy ketal to homopentaprimanone. Homopentaprimanone is oxidzed to a lactone using chloroperbenzoic acid, then catalytically oxidized with ruthenate in aqueous potassium hydroxide with periodate, to produce the α lactol, cleaved by diazomethane in ether to produce a ketone and a methyl carboxylate ester, which undergo a intramolecular addition to a ketal and reduction to a diol when a dilute ether solution is added dropwise to a sodium ammonia solution, which is then converted to hydroxyhomopentaprimanone by Corey–Kim oxidation. Hydroxyhomopentaprimanone is then converted to the tosylate, which can undergo a Favorskii rearrangement in aqueous 20% potassium hydroxide at 80 °C to pentaprismane carboxylic acid which can be decarboxylated to form pentaprismane.

Summary Hypostrophene does not undergo intramolecular [2+2] photocyclization to form pentaprismane, but homohypostrophene does undergo intramolecular [2+2] photocyclization to for homopentaprismane. pentaprismanecarboxylic acid can be synthesized by a favorskii rearrangement of a homopentaprismanone which can be prepared from a homohypostrophenone which can be prepared in a multistep sequence from benzoquinone and a cyclopentadienone