TheAllan–Robinson reaction is thechemical reaction of o-hydroxyarylketones with aromaticanhydrides to formflavones (orisoflavones).[1][2][3][4]
Ifaliphatic anhydrides are used,coumarins can also be formed. (SeeKostanecki acylation.)
The o-hydroxyaryl ketone first undergoestautomerization to form the respectiveenol. Thepi electrons of thedouble bond then attack the electrophilic carbon of the anhydride; acarboxylate anion is subsequently lost as a leaving group. The carboxylate anion then attacks an alpha hydrogen to form an enol. The nucleophilic hydroxyl group then attacks the carbonyl carbon to form a six-memberedheterocyclic ring. A proton is abstracted from the hydroxyl group of the enol to form a ketone, and the remaining hydroxyl group is lost as a leaving group in a concerted step to afford the final product.[4][5]
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