Cyanation

Last updated

In organic synthesis, cyanation is the attachment or substitution of a cyanide group on various substrates. Such transformations are high-value because they generate C-C bonds. Furthermore nitriles are versatile functional groups.

Contents

Cyanation to form sp3 nitriles

Typically, alkyl nitriles are formed via SN1 or SN2-type cyanation with alkyl electrophiles. Illustrative is the synthesis of benzyl cyanide by the reaction of benzyl chloride and sodium cyanide. [1] In some cases cuprous cyanide is used instead of sodium cyanide. [2]

Cyanation of ketones or aldehydes yields the corresponding cyanohydrins, which can be done directly with the cyanide ion (the cyanohydrin reaction) or by using bisulfite, followed by displacement of sulfite: [3] [4]

Cyanation of aldehyde with bisulfite Cyanation of aldehyde with bisulfate.svg
Cyanation of aldehyde with bisulfite

A related reaction is hydrocyanation, which installs the elements of H-CN.

Cyanation of arenes

Cyanation of arenes offers access to benzoic acid derivatives, as well as the utility of aryl nitriles themselves in as fine chemicals:

Cyanation starburst.png

A variety of mechanistically distinct pathways are known to cyanate arenes:

With arene as two-electron electrophile

While the classical Rosenmund Von-Braun reaction utilizes stoichiometric copper(I) cyanide as a cyanation source, [5] newer variants have been developed that are catalytic in copper: [6]

Cat rosenmund.png

In addition, palladium-catalyzed cyanations of aryl halides have been extensively explored. Generally, KCN or its less toxic surrogate Zn(CN)2 are used as nucleophilic cyanide sources. To further diminish toxicity concerns, potassium ferricyanide has also been used as a cyanide source. Catalytic cycles are believed to proceed through a standard Pd (0/II) pathway with reductive elimination forging the key C-C bond. Deactivation of Pd(II) with excess cyanide is a common problem. [7] Palladium catalysis conditions for aryl iodides, bromides, and even chlorides have been developed: [8]

Pd cyanation.png

Nickel-catalyzed cyanations avoid the use of precious metals, and can take advantage of benzyl cyanide or acetonitrile as a cyanide source, via reductive C-C bond cleavage: [9]

Nickel cyanation.png

Sandmeyer cyanation is a means of converting aniline derivatives to benzonitriles. [10] The cyanation is generally postulated to be two-electron, while with radical mediators in absence of metals, the reaction is likely radical. [11]

With arene as a two-electron nucleophile

Metalated arenes can be cyanated with electrophilic cyanide sources, including cyanamides, cyanates, dimethylmalononitrile, or ethyl (ethoxymethylene)cyanoacetate. These methods can proceed with or without transition metal mediation: [12]

Electrophilic cyanation.png

With arene as a radical electrophile

Radical approaches to arene C-H cyanation are known. Photoredox mediators (metallic or organic) are most common: [13] [14]

Photo cyanation.png

Related Research Articles

<span class="mw-page-title-main">Cyanohydrin</span> Functional group in organic chemistry

In organic chemistry, a cyanohydrin or hydroxynitrile is a functional group found in organic compounds in which a cyano and a hydroxy group are attached to the same carbon atom. The general formula is R2C(OH)CN, where R is H, alkyl, or aryl. Cyanohydrins are industrially important precursors to carboxylic acids and some amino acids. Cyanohydrins can be formed by the cyanohydrin reaction, which involves treating a ketone or an aldehyde with hydrogen cyanide (HCN) in the presence of excess amounts of sodium cyanide (NaCN) as a catalyst:

In organic chemistry, a nitrile is any organic compound that has a −C≡N functional group. The prefix cyano- is used interchangeably with the term nitrile in industrial literature. Nitriles are found in many useful compounds, including methyl cyanoacrylate, used in super glue, and nitrile rubber, a nitrile-containing polymer used in latex-free laboratory and medical gloves. Nitrile rubber is also widely used as automotive and other seals since it is resistant to fuels and oils. Organic compounds containing multiple nitrile groups are known as cyanocarbons.

The Heck reaction is the chemical reaction of an unsaturated halide with an alkene in the presence of a base and a palladium catalyst to form a substituted alkene. It is named after Tsutomu Mizoroki and Richard F. Heck. Heck was awarded the 2010 Nobel Prize in Chemistry, which he shared with Ei-ichi Negishi and Akira Suzuki, for the discovery and development of this reaction. This reaction was the first example of a carbon-carbon bond-forming reaction that followed a Pd(0)/Pd(II) catalytic cycle, the same catalytic cycle that is seen in other Pd(0)-catalyzed cross-coupling reactions. The Heck reaction is a way to substitute alkenes.

The Suzuki reaction is an organic reaction, classified as a cross-coupling reaction, where the coupling partners are a boronic acid and an organohalide and the catalyst is a palladium(0) complex. It was first published in 1979 by Akira Suzuki, and he shared the 2010 Nobel Prize in Chemistry with Richard F. Heck and Ei-ichi Negishi for their contribution to the discovery and development of palladium-catalyzed cross-couplings in organic synthesis. This reaction is also known as the Suzuki–Miyaura reaction or simply as the Suzuki coupling. It is widely used to synthesize polyolefins, styrenes, and substituted biphenyls. Several reviews have been published describing advancements and the development of the Suzuki reaction. The general scheme for the Suzuki reaction is shown below, where a carbon-carbon single bond is formed by coupling a halide (R1-X) with an organoboron species (R2-BY2) using a palladium catalyst and a base.

The Sandmeyer reaction is a chemical reaction used to synthesize aryl halides from aryl diazonium salts using copper salts as reagents or catalysts. It is an example of a radical-nucleophilic aromatic substitution. The Sandmeyer reaction provides a method through which one can perform unique transformations on benzene, such as halogenation, cyanation, trifluoromethylation, and hydroxylation.

The Ullmann condensation or Ullmann-type reaction is the copper-promoted conversion of aryl halides to aryl ethers, aryl thioethers, aryl nitriles, and aryl amines. These reactions are examples of cross-coupling reactions.

The Letts nitrile synthesis is a chemical reaction of aromatic carboxylic acids with metal thiocyanates to form nitriles. The reaction includes the loss of carbon dioxide and potassium hydrosulfide. The polar basic substitution reaction was discovered in 1872 by Edmund A. Letts.

<span class="mw-page-title-main">Organocopper chemistry</span> Compound with carbon to copper bonds

Organocopper chemistry is the study of the physical properties, reactions, and synthesis of organocopper compounds, which are organometallic compounds containing a carbon to copper chemical bond. They are reagents in organic chemistry.

In organic chemistry, the Buchwald–Hartwig amination is a chemical reaction for the synthesis of carbon–nitrogen bonds via the palladium-catalyzed coupling reactions of amines with aryl halides. Although Pd-catalyzed C-N couplings were reported as early as 1983, Stephen L. Buchwald and John F. Hartwig have been credited, whose publications between 1994 and the late 2000s established the scope of the transformation. The reaction's synthetic utility stems primarily from the shortcomings of typical methods for the synthesis of aromatic C−N bonds, with most methods suffering from limited substrate scope and functional group tolerance. The development of the Buchwald–Hartwig reaction allowed for the facile synthesis of aryl amines, replacing to an extent harsher methods while significantly expanding the repertoire of possible C−N bond formation.

The Castro–Stephens coupling is a cross coupling reaction between a copper(I) acetylide and an aryl halide in pyridine, forming a disubstituted alkyne and a copper(I) halide.

In organic chemistry, the Kumada coupling is a type of cross coupling reaction, useful for generating carbon–carbon bonds by the reaction of a Grignard reagent and an organic halide. The procedure uses transition metal catalysts, typically nickel or palladium, to couple a combination of two alkyl, aryl or vinyl groups. The groups of Robert Corriu and Makoto Kumada reported the reaction independently in 1972.

<span class="mw-page-title-main">Benzyl cyanide</span> Chemical compound

Benzyl cyanide (abbreviated BnCN) is an organic compound with the chemical formula C6H5CH2CN. This colorless oily aromatic liquid is an important precursor to numerous compounds in organic chemistry.

<span class="mw-page-title-main">Rosenmund–von Braun reaction</span>

The Rosenmund–von Braun synthesis is an organic reaction in which an aryl halide reacts with cuprous cyanide to yield an aryl nitrile.

Organomanganese chemistry is the chemistry of organometallic compounds containing a carbon to manganese chemical bond. In a 2009 review, Cahiez et al. argued that as manganese is cheap and benign, organomanganese compounds have potential as chemical reagents, although currently they are not widely used as such despite extensive research.

Decarboxylative cross coupling reactions are chemical reactions in which a carboxylic acid is reacted with an organic halide to form a new carbon-carbon bond, concomitant with loss of CO2. Aryl and alkyl halides participate. Metal catalyst, base, and oxidant are required.

Metal-catalyzed C–H borylation reactions are transition metal catalyzed organic reactions that produce an organoboron compound through functionalization of aliphatic and aromatic C–H bonds and are therefore useful reactions for carbon–hydrogen bond activation. Metal-catalyzed C–H borylation reactions utilize transition metals to directly convert a C–H bond into a C–B bond. This route can be advantageous compared to traditional borylation reactions by making use of cheap and abundant hydrocarbon starting material, limiting prefunctionalized organic compounds, reducing toxic byproducts, and streamlining the synthesis of biologically important molecules. Boronic acids, and boronic esters are common boryl groups incorporated into organic molecules through borylation reactions. Boronic acids are trivalent boron-containing organic compounds that possess one alkyl substituent and two hydroxyl groups. Similarly, boronic esters possess one alkyl substituent and two ester groups. Boronic acids and esters are classified depending on the type of carbon group (R) directly bonded to boron, for example alkyl-, alkenyl-, alkynyl-, and aryl-boronic esters. The most common type of starting materials that incorporate boronic esters into organic compounds for transition metal catalyzed borylation reactions have the general formula (RO)2B-B(OR)2. For example, bis(pinacolato)diboron (B2Pin2), and bis(catecholato)diborane (B2Cat2) are common boron sources of this general formula.

<span class="mw-page-title-main">Catellani reaction</span>

The Catellani reaction was discovered by Marta Catellani and co-workers in 1997. The reaction uses aryl iodides to perform bi- or tri-functionalization, including C-H functionalization of the unsubstituted ortho position(s), followed a terminating cross-coupling reaction at the ipso position. This cross-coupling cascade reaction depends on the ortho-directing transient mediator, norbornene.

<span class="mw-page-title-main">Ethyl cyanoacetate</span> Chemical compound

Ethyl cyanoacetate is an organic compound that contains a carboxylate ester and a nitrile. It is a colourless liquid with a pleasant odor. This material is useful as a starting material for synthesis due to its variety of functional groups and chemical reactivity.

<span class="mw-page-title-main">3-Bromopyridine</span> Chemical compound


3-Bromopyridine is an organohalide with the formula C5H4BrN. It is a colorless liquid that is mainly used as a building block in organic synthesis.

<span class="mw-page-title-main">Organic thiocyanates</span>

Organic thiocyanates are organic compounds containing the functional group RSCN. the organic group is attached to sulfur: R−S−C≡N has a S–C single bond and a C≡N triple bond.

References

  1. Adams, Roger; Thal, A. F. (1922). "Benzyl cyanide". Organic Syntheses. 2: 9. doi:10.15227/orgsyn.002.0009.
  2. J. V. Supniewski; P. L. Salzberg (1928). "Allyl Cyanide". Org. Synth. 8: 4. doi:10.15227/orgsyn.008.0004.
  3. Mowry, David T. (1948). "The Preparation of Nitriles". Chemical Reviews. 42 (2): 189–283. doi:10.1021/cr60132a001. ISSN   0009-2665. PMID   18914000.
  4. Corson, B. B.; Dodge, R. A.; Harris, S. A.; Yeaw, J. S. (1926). "Mandelic Acid". Org. Synth. 6: 58. doi:10.15227/orgsyn.006.0058.
  5. Warzecha, Klaus-Dieter. "cyanide substitution of bromobenzene".
  6. Wu, Jeff (2002). "Catalytic Rosenmund–von Braun reaction in halide-based ionic liquids". Tetrahedron Letters. 43 (3): 387–389. doi:10.1016/s0040-4039(01)02168-2.
  7. Cohen, Daniel (2015). "Mild Palladium-Catalyzed Cyanation of (Hetero)aryl Halides and Triflates in Aqueous Media". Organic Letters. 17 (2): 202–205. doi: 10.1021/ol5032359 . PMC   4301087 . PMID   25555140.
  8. Jin, Fuqiang (2000). "Palladium-catalyzed cyanation reactions of aryl chlorides". Tetrahedron Letters. 41 (18): 3271–3273. doi:10.1016/s0040-4039(00)00384-1.
  9. Ueda, Yohei (2019). "Nickel-catalyzed cyanation of aryl halides and triflates using acetonitrile via C–CN bond cleavage assisted by 1,4-bis(trimethylsilyl)-2,3,5,6-tetramethyl-1,4-dihydropyrazine". Chemical Science. 10 (4): 994–999. doi: 10.1039/c8sc04437f . PMC   6349056 . PMID   30774893.
  10. H. T. Clarke; R. R. Read (1925). "o-Tolunitrile and p-Tolunitrile". Org. Synth. 4: 69. doi:10.15227/orgsyn.004.0069.
  11. Barbero, Margherita (2016). "Copper-free Sandmeyer cyanation of arenediazonium o-benzenedisulfonimides". Organic & Biomolecular Chemistry. 14 (4): 1437–1441. doi:10.1039/c5ob02321a. hdl: 2318/1554335 . PMID   26676962.
  12. Reeves, Jonathan (2015). "Transnitrilation from Dimethylmalononitrile to Aryl Grignard and Lithium Reagents: A Practical Method for Aryl Nitrile Synthesis". Journal of the American Chemical Society. 137 (29): 9481–9488. doi:10.1021/jacs.5b06136. PMID   26151426.
  13. Ravelli, Davide; Protti, Stefano; Fagnoni, Maurizio (2016). "Carbon-Carbon Bond Forming Reactions via Photogenerated Intermediates". Chemical Reviews. 116 (17): 9850–9913. doi:10.1021/acs.chemrev.5b00662. PMID   27070820.
  14. Li, Jie Jack (2015). C-H Bond Activation in Organic Synthesis. CRC Press, Taylor & Francis Group.