Cycloaddition: Difference between revisions

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Thermal cycloadditions are those cycloadditions where the reactants are in the ground electronic state. They usually have (4''n'' + 2) π electrons participating in the starting material, for some integer ''n''. These reactions occur for reasons of [[orbital symmetry]] in a [[suprafacial]]-suprafacial (''syn''/''syn'' stereochemistry) in most cases. Very few examples of [[antarafacial]]-antarafacial (''anti''/''anti'' stereochemistry) reactions have also been reported. There are a few examples of thermal cycloadditions which have 4''n'' π electrons (for example the [2 + 2]-cycloaddition). These proceed in a suprafacial-antarafacial sense (''syn''/''anti'' stereochemistry), such as the cycloaddition reactions of [[ketene]] and [[Allenes|allene]] derivatives, in which the [[orthogonal]] set of [[p orbital]]s allows the reaction to proceed via a crossed [[transition state]], although the analysis of these reactions as [_π2_s + _π2_a] is controversial. Strained alkenes like ''trans''-cycloheptene derivatives have also been reported to react in an antarafacial manner in [2 + 2]-cycloaddition reactions.

[[William von Eggers Doering|Doering]] (in a personal communication to [[Robert Burns Woodward|Woodward]]) discoveredreported that [[Fulvalene (compound class)|heptafulvalene]] and tetracyanoethylene can react in a suprafacial-antarafacial [14 + 2]-cycloaddition. However, Thisthis resultreaction was later confirmedfound andto extendedbe bystepwise, Erdenas andit Kaufmann,also who reportedproduced the suprafacialWoodward-antarafacialHoffmann cycloadditionforbidden of heptafulvalene with ''N''suprafacial-phenyltriazolinedione.<ref>{{Citesuprafacial journal|last1=Erden|first1=Ihsan|last2=KauFmann|first2=Dieter|date=1981-01-01|title=Cycloadditionsreaktionenproduct desunder heptafulvalens|url=https://dx.doi.org/10.1016/0040-4039%2881%2980058-5|journal=Tetrahedronkinetic Letters|language=de|volume=22|issue=3|pages=215–218|doi=10conditions.1016/0040-4039(81)80058-5|issn=0040-4039}}</ref>

<ref>{{Cite |last1=Izzotti|first1=Anthony|

last2=Gleason|first2=Gleason|

date=2022-06-07|

title=Do Antarafacial Cycloadditions Occur? Cycloaddition of Heptafulvalene with Tetracyanoethylene|

url=https://chemistry-europe.onlinelibrary.wiley.com/doi/epdf/10.1002/chem.202201418|

journal=Chemistry: a European Journal|

doi=10.1002/chem.202201418}}

</ref>

Erden and Kaufmann had previously found that the cycloaddition of heptafulvalene and N-phenyltriazolinedione also gave both suprafacial-antarafacial and suprafacial-suprafacial products. <ref>{{Cite journal|last1=Erden|first1=Ihsan|last2=KauFmann|first2=Dieter|date=1981-01-01|title=Cycloadditionsreaktionen des heptafulvalens|url=https://dx.doi.org/10.1016/0040-4039%2881%2980058-5|journal=Tetrahedron Letters|language=de|volume=22|issue=3|pages=215–218|doi=10.1016/0040-4039(81)80058-5|issn=0040-4039}}</ref>

[[File:14plus2.png|center|frameless|400x400px]]