Search for Long-lived 1,3-carbodications and Preparation of the Persistent 1,1,3,3-tetracyclopropyl-1,3-propanediyl Dication
Several substituted versions of 1,3-propanediol were ionized under a variety of superacidic conditions, and the product carbocations and carboxonium species were characterized by 13C NMR spectroscopy at low temperatures. 1,1,3-Triphenyl-1,3-propanediol (19), and 1,1,3,3-tetraphenyl- 1,3-propanediol (20), upon ionization in FSO3H/SO2ClF or SbF5- FSO3H/SO2ClF solution at -78 °C gave the disproportionated cationic species, 1,1-diphenylethyl cation (24) and protonated benzaldehyde (25) or protonated benzophenone (26). At lower temperatures (-130 °C) they yielded the allyl cations, 29 and 30, as the only products. Diol 23 was also ionized at -78 °C to give a 1:1 mixture of tricyclopropylmethyl cation (27) and O- protonated dicyclopropyl ketone (28). The ionization of 1,1,3,3- tetracyclopropyl-1,3-propanediol (21) in SbF5/SO2ClF, on the other hand, gave the stable 1,3-carbodication, that is, 1,1,3,3-tetracyclopropyl-1,3- propanediyl dication (33). The structures and the 13C NMR chemical shifts for the carbodication 33 and the allyl cations 29 and 30 were also computed using DFT/IGLO methods.
G. A. Olah et al., "Search for Long-lived 1,3-carbodications and Preparation of the Persistent 1,1,3,3-tetracyclopropyl-1,3-propanediyl Dication," Journal of the American Chemical Society, American Chemical Society (ACS), Nov 1999.
The definitive version is available at http://dx.doi.org/10.1021/ja992321k
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