Vilsmeier-Haack reaction

Vilsmeier-Haack reaction

The Vilsmeier-Haack reaction (also called the Vilsmeier reaction) is the chemical reaction of a substituted amide (1) with phosphorus oxychloride and an activated arene (3) to produce an aryl aldehyde or ketone (5).Ref|Vilsmeier1927Ref|Meth-Cohn1991Ref|Campaigne1953 The reaction of a substituted amide with phosphorus oxychloride gives a substituted chloroiminium ion (2), also called the Vilsmeier reagent. The initial product is an iminium ion (4b), which is hydrolyzed to the corresponding aromatic ketone or aldehyde.

For example, benzanilide and dimethylaniline react with phosphorus oxychloride to produce an unsymmetrical diaryl ketone.Ref|3 Similarly, anthracene can be formylated exclusively at the 9-position.Ref|4

Reaction mechanism

The reaction of the amide with phosphorus oxychloride produces an electrophilic iminium cation. The subsequent electrophilic aromatic substitution produces an iminium ion intermediate, which is hydrolyzed to give the desired aryl ketone or aryl aldehyde.

Applications

One recent application of this reaction involved a new synthetic route to tris(4-formylphenyl)amine Ref|5 from triphenylamine which by known procedures only resulted in a modest chemical yield of 16%. It was found that this low yield was caused by deactivation of the remaining benzene ring by the imine groups on the other two phenyl groups in the third formylation step. The procedure was modified by taking the reaction to di-imine compound followed by hydrolysis to the di-formyl compound and then (with final position reactived) a separate formylation to the tri substituted compound.

References

* Anton Vilsmeier; Haack, A. "Ber." 1927, "60", 119.
* Meth-Cohn, O.; Stanforth, S. P. "Comp. Org. Syn." 1991, "2", 777-794. (Review)
* "Formylation of dimethylaniline." Campaigne, E.; Archer, W. L. "Org. Syn.", Coll. Vol. 4, p.331 (1963); Vol. 33, p.27 (1953). ( [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv4p0331 Article] )
* "Vilsmeyer-Haack reaction of benzanilide and dimethylaniline." Hurd, C. D.; Webb. C. N. "Org. Syn.", Coll. Vol. 1, p.217 (1941); Vol. 7, p.24 (1927). ( [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv1p0217 Article] )
* "Formylation of anthracene." Fieser, F. L.; Hartwell, J. L.; Jones, J. E.; Wood, J. H.; Bost, R. W. "Org. Syn.", Coll. Vol. 3, p.98 (1955); Vol. 20, p.11 (1940). ( [http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0098 Article] )
* "Practical and Efficient Synthesis of Tris(4-formylphenyl)amine, a Key Building Block in Materials Chemistry" Thomas Mallegol, Said Gmouh, Mohamed Aït Amer Meziane, Mireille Blanchard-Desce, Olivier Mongin "Synthesis" 2005, 1771-1774. (DOI|10.1055/s-2005-865336)

ee also

* Formylation reaction


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