[12]Annulynes

摘要

Only one isomer of o-benzyne ([6]annulyne or 1,2-didehydrobenzene) exists,but the dehydro analogue of the "ring-opened double benzene",[12]annulyne,was generated in several isomeric forms.1,5-Hexadiyne undergoes self-condensation in the presence of potassium tert-butoxide to yield two isomers of [12]annulyne (3,11-di-trans-[12]annulyne and 5,9-di-trans-[12]annulyne),both of which exhibit a weak paratropic ring current in their ~1H NMR spectra and are oxygen sensitive.They can be reduced to their respective dianions,which are diatropic.A third isomer (3,9-di-trans-[12]annulyne) was generated via the complete dehydrohalogenation of hexabromocyclododecene and found to be much less stable but can be tamed via one- or two-electron reduction.A tight association of the cation (K~+) with the p_y-orbitals within the alkyne moiety results in an unusually low-field resonance for an adjacent external proton.