1,2,3-Cyclohexatriene is an unstable chemical compound with the molecular formula . It is an unusual isomer of benzene in which the three double bonds are cumulated.
In 1990, 1,2,3-cyclohexatriene was first prepared by reacting a cyclohexadiene derivative with cesium fluoride.  The product was too reactive to be isolated on its own, so its existence was confirmed by trapping via a cycloaddition reaction.
1,2,3-Cyclohexatriene and its derivatives undergo a variety of reactions including cycloadditions, nucleophilic additions, and σ-bond insertions, and therefore they can be versatile reagents for organic synthesis.