Voigt reaction

The Voigt reaction (also called Voigt condensation ) is a name reaction in organic chemistry , which was named after Karl Voigt and was first described by him in 1886. It is a condensation reaction that leads to the formation of secondary or tertiary α-amino ketones .

Overview reaction

In the Voigt reaction, a primary or secondary amine (R ¹ = H , alkyl or aryl group ; R ² = alkyl group) reacts with benzoin with elimination of water to form a secondary or tertiary α-amino ketone. Hydrochloric acid or phosphorus pentoxide is usually used as the condensation reagent . For steric reasons, the reaction works particularly well with primary amines, although some complex primary amines with great steric hindrance are an exception and do not react according to the Voigt reaction. Few secondary amines react with benzoin for the same reason. Relatively simply structured secondary amines, e.g. B. pyrrolidine or piperidine , but provide the corresponding tertiary α-amino-ketone.

Reaction mechanism

It is assumed that the reaction is initiated by an attack by the amino group 1 on the carbonyl group of the benzoin 2 . After intramolecular proton transfer from ammonium to the hydroxyl group and protonation of the compound, the imine 3 is formed after elimination of water . This tautomerizes to enamine 4 in the next step . The α-amino-ketone 5 is formed by a further [1,3] hydrogen shift and subsequent deprotonation .

Sample reaction

When stoichiometric amounts of 2-aminopyridine and benzoin are combined, a secondary α-amino-ketone is formed in the presence of heat , hydrochloric acid as the condensation reagent and toluene as the solvent, with elimination of water .

application

The Voigt reaction is a good way to synthesize optically active α-amino-ketones. Resulting α-amino-ketone can also be α-amino alcohols containing two phenyl groups include, reduces be.

Individual evidence

↑ E. von Meyer, Karl Voigt: V. Ueber the action of primary aromatic amines on Benzoïn . In: Journal for Practical Chemistry . tape 34 , no. 1 , 1886, p. 1-27 , doi : 10.1002 / prac.18860340101 .
↑ ^a ^b ^c ^d ^e Zerong Wang: Voigt Reaction . In: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, Inc., Hoboken, NJ, USA 2010, ISBN 978-0-470-63885-9 , pp. 2888-2891 , doi : 10.1002 / 9780470638859.conrr645 .
↑ H. Surya Prakash Rao, Satish Vijjapu: The Voight reaction on tertiary α-hydroxy ketones . In: Tetrahedron . tape 71 , no. 44 , November 4, 2015, p. 8391-8406 , doi : 10.1016 / j.tet.2015.08.069 .

[1] E. von Meyer, Karl Voigt: V. Ueber the action of primary aromatic amines on Benzoïn . In: Journal for Practical Chemistry . tape 34 , no. 1 , 1886, p. 1-27 , doi : 10.1002 / prac.18860340101 .

[:0-2] Zerong Wang: Voigt Reaction . In: Comprehensive Organic Name Reactions and Reagents . John Wiley & Sons, Inc., Hoboken, NJ, USA 2010, ISBN 978-0-470-63885-9 , pp. 2888-2891 , doi : 10.1002 / 9780470638859.conrr645 .

[3] H. Surya Prakash Rao, Satish Vijjapu: The Voight reaction on tertiary α-hydroxy ketones . In: Tetrahedron . tape 71 , no. 44 , November 4, 2015, p. 8391-8406 , doi : 10.1016 / j.tet.2015.08.069 .