Carboximidate

Imidates may be generated by a number of synthetic routes,{{cite journal|last=Roger|first=Robert|author2=Neilson, Douglas G.|title=The Chemistry of Imidates.|journal=Chemical Reviews|date=1961|volume=61|issue=2|pages=179–211|doi=10.1021/cr60210a003}} but are in general formed by the Pinner reaction. This proceeds via the acid catalyzed attack of nitriles by alcohols.

File:Pinner Reaktion Grundmecha Version 1-Seite001.svg

Imidates produced in this manner are formed as their hydrochloride salts, which are sometimes referred to as Pinner salts. Carboximidates are also formed as intermediates in the Mumm rearrangement and the Overman rearrangement.

An amidate/imidate anion is formed upon deprotonation of an amide or imidic acid. Since amides and imidic acids are tautomers, they form the same anion upon deprotonation. The two names are thus synonyms describing the same anion, although arguably, imidate refers to the resonance contributor on the left, while amidate refers to the resonance contributor on the right. However, they are distinguished when they act as ligands for transition metals, with O-bound species referred to as imidates and N-bound species referred to as amidates. They can be considered aza-substituted analogues of enolates with the formula R-N=C(O⁻)R.

Image:Amidate-resonance-2D-skeletal.png

Carboximidates are good electrophiles and undergo a range of addition reactions; with aliphatic imidates generally reacting faster than aromatic imidates. They can be hydrolyzed to give esters and by an analogous process react with amines (including ammonia) to form amidines. Aliphatic imidates react with an excess of alcohol under acid catalysis to form orthoesters RC(OR)₃, aromatic imidates can also be converted but far less readily.

File:Pinner Übersicht Version 2.svg

The Chapman rearrangement is the thermal conversion of aryl N-arylbenzimidates to the corresponding amides, via intramolecular migration of an aryl group from oxygen to nitrogen.{{Cite journal|author1=Schulenberg, J. W. |author2=Archer, S. |title=The Chapman Rearrangement|journal=Organic Reactions|year=1965|volume=14|pages=1–51 |doi=10.1002/0471264180.or014.01|isbn=0471264180}} It is named after Arthur William Chapman, who first described it,{{cite journal |last1=Chapman |first1=Arthur William |title=CCLXIX.—Imino-aryl ethers. Part III. The molecular rearrangement of N-phenylbenziminophenyl ether |journal=J. Chem. Soc., Trans. |date=1925 |volume=127 |pages=1992–1998 |doi=10.1039/CT9252701992}} and is conceptually similar to the Newman–Kwart rearrangement.

Image:Chapman rearrangement.svg

Image:Benzyl 2,2,2-trichloroacetimidate.svg

Carboximidates can act as protecting group for alcohols.{{cite book|last=Wuts|first=Peter G. M.|title=Protective groups in organic synthesis.|year=2006|publisher=WILEY|location=Hoboken, N.J.|isbn=978-0-471-69754-1|page=244|edition=4th|author2=Greene, Theodora W.}} For example, the base catalyzed reaction of benzyl alcohol upon trichloroacetonitrile yields a trichloroacetimidate. This species has orthogonal stability to acetate and TBS protections and may be cleaved by acid hydrolysis.{{cite journal|last=Yu|first=Biao|author2=Yu, Hai |author3=Hui, Yongzheng |author4= Han, Xiuwen |title=Trichloroacetimidate as an Efficient Protective Group for Alcohols|journal=Synlett|date=June 1999|volume=1999|issue=6|pages=753–755|doi=10.1055/s-1999-2736}}

• Amidines
• Esters
• Imidoyl chloride — the "acyl chloride" variant
• Oxazoline — the corresponding 5-membered heterocycle

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Category:Functional groups