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
are versatile functional groups.
Cyanation to form sp3 nitriles
Typically, alkyl nitriles are formed
via S
N1 or S
N2-type cyanation with alkyl electrophiles. Illustrative is the synthesis of
benzyl cyanide by the reaction of
benzyl chloride and sodium cyanide.
In some cases
cuprous cyanide is used instead of sodium cyanide.
Cyanation of ketones or aldehydes yields the corresponding Cyanohydrin, which can be done directly with the cyanide ion (the cyanohydrin reaction) or by using bisulfite, followed by displacement of sulfite:
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:
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
Stoichiometry copper(I) cyanide as a cyanation source,
newer variants have been developed that are
Catalysis in
copper:
In addition, palladium-catalyzed cyanations of
have been extensively explored. Generally, KCN or its less toxic surrogate
Zinc cyanide are used as
Nucleophile cyanide sources. To further diminish
toxicity concerns, potassium ferricyanide has also been used as a cyanide source.
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.
Palladium catalysis conditions for aryl iodides, bromides, and even chlorides have been developed:
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:
Sandmeyer cyanation is a means of converting
aniline derivatives to benzonitriles.
The cyanation is generally postulated to be two-electron, while with radical mediators in absence of metals, the reaction is likely radical.
With arene as a two-electron nucleophile
Metalated arenes can be cyanated with
Electrophile cyanide sources, including
Cyanamide,
Cyanate, dimethylmalononitrile, or ethyl (ethoxymethylene)cyanoacetate. These methods can proceed with or without transition metal mediation:
With arene as a radical electrophile
Radical approaches to arene C-H cyanation are known. Photoredox mediators (metallic or organic) are most common:
