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[[File:Dyotropic rearrangement.svg|thumb|Dyotropic rearrangements of Type I (above) and Type II (below)]]

A '''dyotropic reaction''' (from the [[Ancient Greek|Greek]] ''dyo'', meaning two) in [[organic chemistry]] is a type of [[organic reaction]] and more specifically a [[pericyclic]] [[valence isomerization]] in which two [[sigma bonds]] simultaneously migrate [[Intramolecular reaction|intramolecular]]ly.<ref>''Dyotropic Reactions: Mechanisms and Synthetic Applications'' 
Israel Fernandez Fernando P. Cossıo and Miguel A. Sierra [[Chem. Rev.]] '''2009''', Article ASAP {{doi|10.1021/cr900209c}}</ref> The reaction type is of some relevance to organic chemistry because it can explain how certain reactions occur and because it is a synthetic tool in the synthesis of organic molecules for example in total synthesis. It was first described by [[Manfred T. Reetz]]  in 1971 <ref>''Dyotropic Rearrangements, a New Class of Orbital-Symmetry Controlled Reactions''. Type I Manfred T. Reetz [[Angewandte Chemie International Edition in English]] '''1971''' Volume 11 Issue 2, Pages 129 - 130 {{doi|10.1002/anie.197201291}}</ref><ref>''Dyotropic Rearrangements, a New Class of Orbital-Symmetry Controlled Reactions. Type II''
[[Angewandte Chemie International Edition in English]] '''1971''' Volume 11, Issue 2, Date: February 1972, Pages: 130-131 Manfred T. Reetz {{doi|10.1002/anie.197201311}}</ref>
In a '''type I reaction''' two [[substituent|migrating groups]] interchange their relative positions and a '''type II reaction '''  involves migration to new bonding sites without positional interchange.

==Type I rearrangements==
In type I rearrangements (Y-A-B-X conversion to X-A-B-Y) the two migrating groups are oriented [[trans configuration|trans]] to each other and as a result of the rearrangement they migrate to opposite sides. The first example of a dyotropic rearrangement involving a [[carbon-carbon bond]] was reported by [[Cyril A. Grob]] and [[Saul Winstein]].<ref>''Organische und biologische Chemie Mechanismus der Mutarotation von 5,6-Dibromcholestan''  C.A. Grob, S. Winstein [[Helvetica Chimica Acta]] Volume 35 Issue 3, Pages 782 - 802 '''1952''' {{doi|10.1002/hlca.19520350315}}</ref> They observed the interconversion of 2 bromine atoms in a certain [[steroid]]. 

In a straightforward example the two bromine atoms in 3-[[tert-butyl]]-trans-1,2-dibromohexane [[mutarotation|mutarotate]] by heating.<ref>''Substituent effects on the formation and equilibration of trans-1,2-dibromocyclohexanes''  P. L. Barili, G. Bellucci, G. Berti, F. Marioni, A. Marsili, I. Morelli, [[J. Chem. Soc.]] D, '''1970''', (21),1437-1438 {{doi|10.1039/C29700001437}}</ref> In the [[transition state]] both bromine atoms connect symmetrically to both carbon atoms on opposite sides and the reaction is [[concerted]]. Stepwise mechanisms in dyotropic reactions have also been investigated. 
:[[File:Dyotropic reaction Barili 1970.svg|Dyotropic reaction Barili 1970]]

In organic synthesis an important application is the conversion of 4-substituted-gamma-[[lactone]]s to [[butyrolactone]]s. Type I dyotropic rearrangements also occur around [[carbon-oxygen bond]]s, such as the thermal equilibration of (R<sub>3</sub>Si<sup>1</sup>)R<sub>2</sub>C-O-Si<sup>2</sup>R<sub>3</sub> to (R<sub>3</sub>Si<sup>2</sup>)R<sub>2</sub>C-O-Si<sup>1</sup>R<sub>3</sub>.<ref>{{cite journal |last1=Reetz |first1=M.T. |title=Dyotropic Rearrangements and Related σ-σ Exchange Processes |journal=Advances in Organometallic Chemistry |date=1977 |volume=16 |pages=33–65 |doi=10.1016/S0065-3055(08)60557-2|isbn=9780120311163 }}</ref>{{rp|36}} The [[1,2-Wittig rearrangement]] can also be considered an example of this reaction type. More dyotropic reactions are found involving N-O bonds and N-N bonds.

==Type II rearrangements==
Type II rearrangements often involve double hydrogen migration in a carbon skeleton. This reaction type can be found in certain [[transfer hydrogenation]]s. An example is hydrogen transfer in syn-sesquinorbornene
disulfones.<ref>''Quantitation of proximity effects on rate. A case study involving dyotropic hydrogen migration within syn-sesquinorbornene disulfones carrying central substituents having different spatial demands'' [[Leo A. Paquette]], Mark A. Kesselmayer, Robin D. Rogers [[J. Am. Chem. Soc.]], '''1990''', 112 (1), pp 284–291 {{doi|10.1021/ja00157a044}}</ref><ref>''Intramolecular reaction rate is not determined exclusively by the distance separating reaction centers. The kinetic consequences of modulated ground state strain on dyotropic hydrogen migration in systems of very similar geometric disposition'' Leo A. Paquette, George A. O'Doherty, Robin D. Rogers [[J. Am. Chem. Soc.]], '''1991''', 113 (20), pp 7761–7762 {{doi|10.1021/ja00020a048}}</ref>
:[[File:Dyotropic rearrangement paquette 1991.svg|Dyotropic rearrangement paquette 1991]]

==References==
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[[Category:Organic reactions]]