99808-96-5Relevant academic research and scientific papers
- and Pagodane Dications: Frozen Two-Electron Woodward-Hoffmann Transition-State Models
Prakash, G. K. Surya,Krishnamurthy, V. V.,Herges, Rainer,Bau, Robert,Yuan, Hanna,et al.
, p. 7764 - 7772 (2007/10/02)
- and pagodanes 1/21 were oxidized in SbF5/SO2ClF at -78 deg via two-electron removal from the central cyclobutane ring to give the dications 9 and 24, respectively.Dication 9 is also formed selectively by two-electron oxidation of a diene valence isomer of 1(19) and by ionization of the Br2 adduct of 1 (18).The unique dication 9 is stable at ambient temperature for hours, while the bishomologous 24 rearranges to a bisallylic dication, probably 28, even at -78 deg C.The tight structural prerequisites for the stability of such dications are further substantiated by the observation that from several related cyclobutanoid cage compounds 29-34, when exposed to the same oxidative conditions, no distinct dications could be observed.On the basis of 1H and 13C NMR chemical shift criteria, supported by pertinent SCF-MO calculations, the dications obtained are considered as novel four-center/two-electron delocalized bishomoaromatic species, which resemble two-electron Woodward-Hoffmann transition states and owe their unprecedented character to their specific rigid farmework.The reliability of the calculations in handling cage molecules of this type and size is evaluated in a comparison with structural data provided by single-crystal X-ray structure determinations for - and pagodanes 1/21 and dimethoxy product 16 obtained from quenching experiments with methanol.
