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.[1] 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.[2][3] 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.
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 change
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.[4] 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.[5] 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.
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 change
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.[6][7]
References change
- ↑ Dyotropic Reactions: Mechanisms and Synthetic Applications Israel Fernandez Fernando P. Cossıo and Miguel A. Sierra Chem. Rev. 2009, Article ASAP doi:10.1021/cr900209c
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ 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
- ↑ 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