Dyotropic reaction

A dyotropic reaction is a type of chemical reaction. It is when an organic compound changes its structure. Two substituents jump from one place on the molecule to another. It is a pericyclic valence isomerization when two sigma bonds move at the same time to a new place on the same molecule.Dyotropic Reactions: Mechanisms and Synthetic Applications 
Israel Fernandez Fernando P. Cossıo and Miguel A. Sierra Chem. Rev. 2009, Article ASAP  Dyotropic reactions are important in organic chemistry. They can explain how certain reactions work. Dyotropic reactions can be a useful step in making large and complicated molecules. Dyotropic reactions were first described by Manfred T. Reetz in 1971.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 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  The name "dyotropic reaction" comes from the Greek word dyo meaning "two." "Rearrangement" means that the reaction changes the bonds between atoms on a single molecule.
Dyotropic rearrangement
In a type I reaction, two migrating groups trade their relative positions. 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 to each other. The reaction leaves both groups on the opposite sides. The first example of a dyotropic rearrangement involving a carbon-carbon bond was reported by Cyril A. Grob and Saul Winstein.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  They saw the exchange of two bromine atoms in a certain steroid. 

In a simple example, the two bromine atoms in 3-tert-butyl-trans-1,2-dibromohexane mutarotate by heating.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  In the transition state both bromine atoms connect symmetrically two both carbon atoms on opposite sides and the reaction is concerted. Chemists have also investigated stepwise mechanisms in dyotropic reactions. 
Dyotropic reaction Barili 1970

In organic synthesis, an important dyotropic reaction is the conversion of 4-substituted-gamma-lactones to butyrolactones. Type I dyotropic rearrangements also occur around carbon-oxygen bonds. One example is using heat to change RRSi1R3C-O-Si2R3 to RRSi2R3C-O-Si1R3.  (This reaction can go in both directions depending on temperature.) Another example is the 1,2-Wittig rearrangement. Dyotropic reactions can also happen with N-O bonds or N-N bonds.

Type II rearrangements
Type II rearrangements often involve two hydrogen atoms moving along a carbon skeleton. This reaction type can be found in certain transfer hydrogenations. An example is hydrogen transfer in syn-sesquinorbornene
disulfones.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 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 
Dyotropic rearrangement paquette 1991

References

Category:Organic reactions