The Demjanov rearrangement is the

chemical reaction A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and break ...

of primary

amine In chemistry, amines (, ) are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Amines are formally derivatives of ammonia (), wherein one or more hydrogen atoms have been replaced by a substituent su ...

s with

nitrous acid Nitrous acid (molecular formula ) is a weak and monoprotic acid known only in solution, in the gas phase and in the form of nitrite () salts. Nitrous acid is used to make diazonium salts from amines. The resulting diazonium salts are reagents ...

to give rearranged

alcohol Alcohol most commonly refers to: * Alcohol (chemistry), an organic compound in which a hydroxyl group is bound to a carbon atom * Alcohol (drug), an intoxicant found in alcoholic drinks Alcohol may also refer to: Chemicals * Ethanol, one of sev ...

s. It involves substitution by a

hydroxyl In chemistry, a hydroxy or hydroxyl group is a functional group with the chemical formula and composed of one oxygen atom covalently bonded to one hydrogen atom. In organic chemistry, alcohols and carboxylic acids contain one or more hydrox ...

group with a possible

ring expansion Ring expansion and ring contraction reactions in the course of organic synthesis refer to a set of reactions which can lead to the expansion or contraction of an existing ring. This often makes it possible to access structures that would be diff ...

. It is named after the Russian chemist

Nikolai Jakovlevich Demjanov Nikolay Yakovlevich Demyanov (russian: Никола́й Я́ковлевич Демья́нов; , Tver – March 19, 1938, Moscow), also known as Demjanov and Demjanow, was a Russian organic chemist and a member of the USSR Academy of Sciences (1 ...

(Dem'anov, Demianov) (1861–1938). : Demjanov Rearrangement Scheme

Reaction mechanism

The reaction process begins with

diazotization Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. General properti ...

of the amine by nitrous acid. The diazonium group is a good

leaving group In chemistry, a leaving group is defined by the IUPAC as an atom or group of atoms that detaches from the main or residual part of a substrate during a reaction or elementary step of a reaction. However, in common usage, the term is often limited ...

, forming

nitrogen gas Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at sevent ...

when displaced from the organic structure. This displacement can occur via a rearrangement (path A), in which one of the

sigma bond In chemistry, sigma bonds (σ bonds) are the strongest type of covalent chemical bond. They are formed by head-on overlapping between atomic orbitals. Sigma bonding is most simply defined for diatomic molecules using the language and tools o ...

s adjacent to the diazo group migrates. This migration results in an expansion of the ring. The resulting carbocation is then attacked by a molecule of water. Alternately, the diazo group can be displaced directly by a molecule of water in an S_N2 reaction (path B). Both routes lead to formation of an

Uses

The Demjanov rearrangement is a method to produce a 1-carbon ring enlargement in four, five or six membered rings. The resulting five, six, and seven-membered rings can then be used in further synthetic reactions. It has been shown that the Demjanov reaction is susceptible to

regioselectivity In chemistry, regioselectivity is the preference of chemical bonding or breaking in one direction over all other possible directions. It can often apply to which of many possible positions a reagent will affect, such as which proton a strong base ...

. One example of this is a study conducted by D. Fattori looking at the regioselectivity of the Demjanov rearrangement in one-carbon enlargements of naked sugars. It showed that when an ''exo'' methylamine underwent Demjanov nitrous acid deamination, ring enlargement was not produced. : However, when the ''endo'' methylamine underwent the same conditions, a mixture of rearranged alcohols were produced. :

Problems

This rearrangement also leads to a substituted, but not expanded, byproduct. Thus it can be difficult to isolate the two products and acquire the desired yield. Also, stereoisomers are produced depending on the direction of addition of the water molecule and other molecules may be produced depending on rearrangements.

Future uses

Current research is exploring the possibilities of various directing groups to influence the selectivity of products in the Demjanov rearrangement, such as tin or silicon.This may lead to increased success with the Demjanov, as it would allow more control in the reaction and increase the desired product yield. The rearrangement is incredibly useful, but using it can sometimes prove ineffective by the difficulty of creating the preferred product. Thus if directing groups are possible, this would greatly improve the applicability of the Demjanov.

Variations

Tiffeneau-Demjanov rearrangement

The Tiffeneau-Demjanov rearrangement (after

Marc Tiffeneau Marc Émile Pierre Adolphe Tiffeneau (November 5, 1873 – May 20, 1945) was a French chemist who co-discovered the Tiffeneau-Demjanov rearrangement. In 1899 he graduated from the École de pharmacie de Paris, and afterwards began work as a ...

and

Nikolai Demjanov Nikolay Yakovlevich Demyanov (russian: Никола́й Я́ковлевич Демья́нов; , Tver – March 19, 1938, Moscow), also known as Demjanov and Demjanow, was a Russian organic chemist and a member of the USSR Academy of Sciences ...

) is a variation of the Demjanov rearrangement, which involves both a

and the production of a

ketone In organic chemistry, a ketone is a functional group with the structure R–C(=O)–R', where R and R' can be a variety of carbon-containing substituents. Ketones contain a carbonyl group –C(=O)– (which contains a carbon-oxygen double bon ...

by using

sodium nitrite Sodium nitrite is an inorganic compound with the chemical formula NaNO2. It is a white to slightly yellowish crystalline powder that is very soluble in water and is hygroscopic. From an industrial perspective, it is the most important nitrite ...

and

hydrogen cation In chemistry, the hydron, informally called proton, is the cationic form of atomic hydrogen, represented with the symbol . The general term "hydron", endorsed by the IUPAC, encompasses cations of hydrogen regardless of their isotopic composition ...

. Using the Tiffeneau-Demjanov reaction is often advantageous as, while there are rearrangements possible in the products, the reactant always undergoes ring enlargement. As in the Demjanov rearrangement, products illustrate regioselectivity in the reaction. Migratory aptitudes of functional groups dictate rearrangement products.

Use of diazomethane

Diazomethane Diazomethane is the chemical compound CH2N2, discovered by German chemist Hans von Pechmann in 1894. It is the simplest diazo compound. In the pure form at room temperature, it is an extremely sensitive explosive yellow gas; thus, it is almos ...

also produces ring enlargement, and its reaction is mechanistically similar to the Tiffeneau-Demjanov rearrangement.

References

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