spiropentadiene
{{Chembox
| verifiedrevid = 443726752
| ImageFile = Spiro-C5H4.png
| ImageSize = 100px
| PIN = Spiro[2.2]penta-1,4-diene
| OtherNames = Bowtiediene; Spiropenta-1,4-diene
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|correct|??}}
| CASNo = 1727-65-7
| ChemSpiderID = 35807558
| PubChem = 14901520
| SMILES = C1=CC21C=C2
| StdInChI=1S/C5H4/c1-2-5(1)3-4-5/h1-4H
| StdInChIKey = JXGJFWLYGSVFBS-UHFFFAOYSA-N
}}
|Section2={{Chembox Properties
| C=5 | H=4
| Appearance =
| Density =
| MeltingPt =
| BoilingPt =
| Solubility = }}
|Section3={{Chembox Hazards
| MainHazards =
| FlashPt =
| AutoignitionPt = }}
}}
Spiropentadiene, or bowtiediene, is a hydrocarbon with formula {{chem|C|5|H|4}}. The simplest spiro-connected diene, it is very unstable—decomposing even below −100 °C—due to its high bond strain and does not occur in nature. Its synthesis was reported in 1991.{{Cite journal| doi = 10.1021/ja00013a067| title = Spiropentadiene| year = 1991| last1 = Billups | first1 = W. E.| last2 = Haley | first2 = M. M.| journal = Journal of the American Chemical Society| volume = 113| issue = 13| pages = 5084 }}{{Cite news |date=July 13, 1991 |title=Elusive bowtie pinned down - synthesis of spiropentadiene, a carbonaceous compound nicknamed bowtiediene because it is shaped like a bowtie |work=Science News |url=https://www.thefreelibrary.com/Elusive+bowtie+pinned+down.-a011134368 |archive-url=https://web.archive.org/web/20220216121520/https://www.thefreelibrary.com/Elusive+bowtie+pinned+down.-a011134368 |archive-date=2022-02-16}}
Synthesis
Spiropentadiene was synthesised from bistrimethylsilylpropynone 1 by reaction with p-toluenesulfonylhydrazide to tosylhydrazone 2 followed by treatment with sodium cyanoborohydride to allene 3 and followed by two successive reactions with chlorocarbene generated from methyllithium and dichloromethane to spiro compound 5. Spiropentadiene was trapped in a liquid nitrogen trap after reaction with TBAF in a double elimination reaction.
Derivatives
The derivative dichlorospiropentadiene has been reported.{{Cite journal| doi = 10.1016/S0040-4039(99)01293-9| title = Synthesis and characterization of 1,4-dichlorospiropentadiene| year = 1999| last1 = Saini | first1 = R.| last2 = Litosh | first2 = V.| last3 = Daniels | first3 = A.| last4 = Billups | first4 = W.| journal = Tetrahedron Letters| volume = 40| issue = 34| pages = 6157 }} An all-silicon derivative (Si5 frame, (tBuMe2Si)3Si side groups) is also known.{{Cite journal| doi = 10.1126/science.290.5491.504| title = A Stable Bicyclic Compound with Two Si=Si Double Bonds| year = 2000| last1 = Iwamoto | first1 = T.| journal = Science| volume = 290| pages = 504–506| last2 = Tamura | first2 = M.| last3 = Kabuto | first3 = C.| last4 = Kira | first4 = M.| pmid = 11039928| issue = 5491 |bibcode = 2000Sci...290..504I }} In contrast to the carbon parent this compound is stable with a melting point of 216 to 218 °C. The angle between the two rings as measured by X-ray single-crystal analysis is 78°.