Knorr pyrazole synthesis

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The Knorr pyrazole synthesis is a name reaction in organic chemistry that was first described by Ludwig Knorr in 1883 with the reaction of acetoacetate and phenylhydrazine . The reaction is the production of pyrazoles from 1,3-dicarbonyl compounds and hydrazines . The synthesis takes place via a condensation mechanism , which is similar to that of the Paal-Knorr synthesis .

Overview reaction

In the Knorr pyrazole synthesis, 1,3-dicarbonyl compounds react with hydrazine or their derivatives to form a pyrazole. In the case of a substituted hydrazine, a mixture of regioisomers is formed, the substituted heteroatom either next to the substituent R 1 or the substituent R 3 .

Reaction scheme for the Knorr pyrazole synthesis

Reaction mechanism

The proposed mechanism begins with imine formation . When the hydrazine 1 attacks the 1,3-dicarbonyl compound 2 in the 1st step, it is decided which of the two possible products is formed, since both carbonyl carbon atoms could be attacked. For the sake of simplicity, only the formation of one product is described in the mechanism presented here. The other nitrogen atom attacks the other carbonyl group after the imine 3 has been formed. After the elimination of water and thus further imine formation, the pyrazole 4 is obtained.

Reaction mechanism

application

The Knorr pyrazole synthesis is generally used in the production of pyrazole derivatives.

See also

Individual evidence

  1. ↑ a b c d Zerong Wang: Comprehensive Organic Name Reactions and Reagents . tape 3 . John Wiley & Sons, Inc., Hoboken, NJ, USA 2010, ISBN 978-0-470-63885-9 , pp. 1631 , doi : 10.1002 / 9780470638859 .
  2. ↑ Ludwig Knorr: Effect of acetoacetic ester on phenylhydrazine . In: Reports of the German Chemical Society . tape 16 , no. 2 , 1883, p. 2597-2599 , doi : 10.1002 / cber.188301602194 .
  3. ↑ Clarisse L. Habraken, James A. Moore: Heterocyclic Studies. XVI. The Assignment of Isomeric and Tautomeric Structures of Pyrazoles by Nuclear Magnetic Resonance *, 1a, b . In: The Journal of Organic Chemistry . tape 30 , no. 6 , 1965, pp. 1892-1896 , doi : 10.1021 / jo01017a041 .
  4. ↑ Knorr pyrazole synthesis - Name-Reaction.com. Retrieved June 7, 2019 .