1,2,4-Cyclohexatriene synthesis

In 1995, we decided to stop further research on this topic because it seemed a philosophical idea that engages primarily theoreticians with little or no impact on experimental chemistry. That this was a premature decision became obvious at the end of 1995, when we learned from Haas and Zilberg31 about the frequency exaltation of the bond alternating vibrational mode in the l B2U excited state of benzene. This created a link of the purely theoretical notion to an experimental probe. The synthesis of Siegel s distorted benzene32,33 demonstrated that a ground state cyclohexatriene has been finally achieved and that this may be a case where 7r-dis-tortivity is at work. This was followed by a demon-... 

Diercks, R. VoUhardt, K. P. C. Tris(benzocyclobutadieno)benzene, the triangular [4]phenylene with a completely bond-fixed cyclohexatriene ring cobalt-catalyzed synthesis from hexaethynylbenzene and thermal ring opening to l,2 5,6 9,10-tribenzo-3,4,7,8,ll,12-hexadehydro[12]annulene, 7. Am. Chem. Soc. 1986,108, 3150-3152. 

Diercks R, VoUhardt KPC (1986) Novel Synthesis of the Angular [3]Phenylene (Terphe-nylene) by Cobalt-Catalyzed Cydization of Bis(2-ethynylphenyl)ethyne — a Molecule with an Internal Cyclohexatriene Ring. Angew Chem Int Ed Engl 25 266... 

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