Hammick reaction
Hammick reaction | |
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Named after | Dalziel Hammick |
Reaction type | Coupling reaction |
The Hammick reaction, named after Dalziel Hammick, is a chemical reaction in which the thermal decarboxylation of α-picolinic (or related) acids in the presence of carbonyl compounds forms 2-pyridyl-carbinols.[1][2][3]
![The Hammick reaction](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d2/Hammick_Reaction_Scheme.png/300px-Hammick_Reaction_Scheme.png)
Using p-cymene as solvent has been shown to increase yields.[4]
Reaction mechanism
Upon heating α-picolinic acid will spontaneously decarboxylate forming the so-called 'Hammick Intermediate' (3). This was initially thought to be an aromatic ylide, but is now believed to be a carbene[5][6] In the presence of a strong electrophile, such as an aldehyde or ketone, this species will undergo nucleophilic attack faster than proton transfer. After nucleophilic attack intramolecular proton transfer yields the desired carbinol (6).
![The mechanism of the Hammick reaction](https://upload.wikimedia.org/wikipedia/commons/thumb/2/23/Hammick-Reaktion_M-v3.svg/650px-Hammick-Reaktion_M-v3.svg.png)
The scope of the reaction is effectively limited to decarboxylating acids where the carboxyl group is α to the nitrogen, (reactivity has been reported when the acids are located elsewhere on the molecule but with low yields)[7][8] thus suitable substrates are limited to the derivatives of α-picolinic acid[3][9] including the α-carboxylic acids of quinoline and isoquinoline.
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