Dyotropic reaction
Encyclopedia
A dyotropic Reaction in organic chemistry
Organic chemistry
Organic chemistry is a subdiscipline within chemistry involving the scientific study of the structure, properties, composition, reactions, and preparation of carbon-based compounds, hydrocarbons, and their derivatives...

 is a type of organic reaction
Organic reaction
Organic reactions are chemical reactions involving organic compounds. The basic organic chemistry reaction types are addition reactions, elimination reactions, substitution reactions, pericyclic reactions, rearrangement reactions, photochemical reactions and redox reactions. In organic synthesis,...

 and more specifically a pericyclic valence isomerization in which two sigma bonds simultaneously migrate intramolecular
Intramolecular
Intramolecular in chemistry describes a process or characteristic limited within the structure of a single molecule, a property or phenomenon limited to the extent of a single molecule.- Examples :...

ly . 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

In a type I reaction two migrating groups
Substituent
In organic chemistry and biochemistry, a substituent is an atom or group of atoms substituted in place of a hydrogen atom on the parent chain of a hydrocarbon...

 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 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
Carbon-carbon bond
A carbon–carbon bond is a covalent bond between two carbon atoms. The most common form is the single bond: a bond composed of two electrons, one from each of the two atoms. The carbon–carbon single bond is a sigma bond and is said to be formed between one hybridized orbital from each...

 was reported by Cyril A. Grob and Saul Winstein
Saul Winstein
Saul Winstein was the Canadian chemist who discovered the Winstein reaction, in which he argued a non-classical cation was needed to explain the stability of the norbornyl cation. This fueled a debate with Herbert C. Brown over the existence of delocalized cations such as this. Richard F...

 . They observed the interconversion of 2 bromine atoms in a certain steroid
Steroid
A steroid is a type of organic compound that contains a characteristic arrangement of four cycloalkane rings that are joined to each other. Examples of steroids include the dietary fat cholesterol, the sex hormones estradiol and testosterone, and the anti-inflammatory drug dexamethasone.The core...

.

In a straightforward example the two bromine atoms in 3-tert-butyl-trans-1,2-dibromohexane mutarotate
Mutarotation
Mutarotation is the change in the optical rotation that occurs by epimerization...

 by heating . In the transition state
Transition state
The transition state of a chemical reaction is a particular configuration along the reaction coordinate. It is defined as the state corresponding to the highest energy along this reaction coordinate. At this point, assuming a perfectly irreversible reaction, colliding reactant molecules will always...

 both bromine atoms connect symmetrically two both carbon atoms on opposite sides and the reaction is concerted. Stepwise mechanisms in dyotropic reactions have also been investigated.


In organic synthesis an important application is the conversion of 4-substituted-gamma-lactone
Lactone
In chemistry, a lactone is a cyclic ester which can be seen as the condensation product of an alcohol group -OH and a carboxylic acid group -COOH in the same molecule...

s to butyrolactones. Type I dyotropic rearrangements also occur around carbon-oxygen bond
Carbon-oxygen bond
A carbon–oxygen bond is a covalent bond between carbon and oxygen and one of the most abundant in organic chemistry and biochemistry. Oxygen has 6 valence electrons and prefers to share two electrons in bonding with carbon, leaving the remaining 4 nonbonding electrons in 2 lone pairs...

s for example is the thermal equilibration of RRSi1R3C-O-Si2R3 to RRSi2R3C-O-Si1R3. The 1,2-Wittig rearrangement
1,2-Wittig rearrangement
A 1,2-Wittig rearrangement is a categorization of chemical reactions in organic chemistry, and consists of a 1,2-rearrangement of an ether with an alkyllithium compound. The reaction is named for Nobel Prize winning chemist Georg Wittig....

 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
Transfer hydrogenation
Transfer hydrogenation is the addition of hydrogen to a molecule from a source other than gaseous H2. It is applied in industry and in organic synthesis, in part because of the inconvenience and expense of using gaseous H2...

s. An example is hydrogen transfer in syn-sesquinorbornene
disulfones .
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