Einhorn–Brunner reaction
The Einhorn–Brunner reaction is the designation for the
![The Einhorn-Brunner Reaction](http://upload.wikimedia.org/wikipedia/commons/thumb/c/ce/Einhorn-Brunner_Rxn_Numbered.png/600px-Einhorn-Brunner_Rxn_Numbered.png)
Regioselectivity
In the case that the R groups of the imide are different, the reaction has regioselectivity. In their research on the synthesis of 1,2,4-triazoles, Potts determined that the strongest acidic group attached to the side of the imide will be favored for the 3 position on the triazole ring.[5] In the diagram below, if one considers the blue R group to be more acidic in respect to the green, the favored product would be the isomer on the right.
![](http://upload.wikimedia.org/wikipedia/commons/thumb/8/8c/Einhorn-Brunner-Reaktion_%C3%9Cbersicht-v4.svg/600px-Einhorn-Brunner-Reaktion_%C3%9Cbersicht-v4.svg.png)
Mechanism
For clarity in depicting the electron flow of the mechanism, the image below only consists of one of the isomers generated in an Einhorn–Brunner reaction:
![](http://upload.wikimedia.org/wikipedia/commons/thumb/2/27/Einhorn-Brunner-Reaktion_Mechanismus-v3.svg/700px-Einhorn-Brunner-Reaktion_Mechanismus-v3.svg.png)
The first step of the mechanism involves the protonating of the substituted nitrogen of the hydrazine 1, generating the cation 2. Protonated hydrazine 2 protonates the oxygen of one of the carbonyl groups of the imide. This allows for an attack on the electrophilic carbon of the protonated carbonyl group by the primary amino group of the hydrazine, producing 3. The loss of water and subsequent generation of a double bond between the recently formed nitrogen-carbon sigma bond results in the formation of iminiumion 4. 4 undergoes a 1,5-proton shift from the nitrogen to the carbonyl oxygen, seen in 5. Intramolecular attack of the electrophilic carbonyl carbon by the nitrogen, resulting in a 5-membered ring closure of the positively charged 6. Elimination of a water group, and then a proton results in the intermediates of 7 and 8 respectively, and finally results in the formation of 9, one 1,2,4-triazole isomer.[7]
Applications
Related reactions
References
- doi:10.1002/jlac.19053430207.)
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- S2CID 94365050.
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- ^ PMID 15081345.
- ISBN 9780471704508.
- ^ Pattan, S.; Gadhave, P.; Tambe, V.; Dengale, S.; Thakur, D; Hiremath, S.V.; Shete, R.V.; Deotarse, P. (Jan 2012). "Synthesis and evaluation of some novel 1,2,4-triazole derivatives for antmicrobial, antitubercular and anti-inflammatory activities" (PDF). Indian Journal of Chemistry. 51B: 297–301.