1,2,4‐Cyclohexatriene, an Isobenzene, and Bicyclo[4.4.0]deca‐1,3,5,7,8‐pentaene, an Isonaphthalene: Generation and Trapping Reactions

The addition of bromofluorocarbene to cyclopentadiene and indene yields stable geminal endo-fluoro, exo-bromocyclopropane derivatives, which when treated with methyllithium lead to isobenzene 1 and isonaphthalene 2, respectively. These cycloallenes can be trapped in cycloaddition reactions, for example with styrene. This reaction sequence can be converted into a one-pot procedure if dibromocarbene is generated at low temperatures from tetrabromomethane and methyllithium and treated in situ for the subsequent reactions.—Because the synthesis of a new isomer of benzene is not reported every day, the experimental study immediately precedes this profile of isobenzene 1 obtained from quantum chemical calculations. These results include data regarding its heart of formation, equilibrium geometry, racemization, diradical character, IR spectrum, and chemoselectivity in its [2 + 2] cycloaddition reaction with styrene.